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Die zerstörungsfreien Prüfungen von Bauwerken mit Hilfe von Ultraschallmessverfahren haben in den letzten Jahren an Bedeutung gewonnen. Durch Ultraschallmessungen können die Geometrien von Bauteilen bestimmt sowie von außen nicht sichtbare Fehler wie Delaminationen und Kiesnester erkannt werden.
Mit neuartigen, in das Betonbauteil eingebetteten Ultraschallprüfköpfen sollen nun Bauwerke dauerhaft auf Veränderungen überprüft werden. Dazu werden Ultraschallsignale direkt im Inneren eines Bauteils erzeugt, was die Möglichkeiten der herkömmlichen Methoden der Bauwerksüberwachung wesentlich erweitert. Ein Ultraschallverfahren könnte mit eingebetteten Prüfköpfen ein Betonbauteil kontinuierlich integral überwachen und damit auch stetig fortschreitende Gefügeänderungen, wie beispielsweise Mikrorisse, registrieren.
Sicherheitsrelevante Bauteile, die nach dem Einbau für Messungen unzugänglich oder mittels Ultraschall, beispielsweise durch zusätzliche Beschichtungen der Oberfläche, nicht prüfbar sind, lassen sich mit eingebetteten Prüfköpfen überwachen. An bereits vorhandenen Bauwerken können die Ultraschallprüfköpfe mithilfe von Bohrlöchern und speziellem Verpressmörtel auch nachträglich in das Bauteil integriert werden. Für Fertigbauteile bieten sich eingebettete Prüfköpfe zur Herstellungskontrolle sowie zur Überwachung der Baudurchführung als Werkzeug der Qualitätssicherung an. Auch die schnelle Schadensanalyse eines Bauwerks nach Naturkatastrophen, wie beispielsweise einem Erdbeben oder einer Flut, ist denkbar.
Durch die gute Ankopplung ermöglichen diese neuartigen Prüfköpfe den Einsatz von empfindlichen Auswertungsmethoden, wie die Kreuzkorrelation, die Coda-Wellen-Interferometrie oder die Amplitudenauswertung, für die Signalanalyse. Bei regelmäßigen Messungen können somit sich anbahnende Schäden eines Bauwerks frühzeitig erkannt werden.
Da die Schädigung eines Bauwerks keine direkt messbare Größe darstellt, erfordert eine eindeutige Schadenserkennung in der Regel die Messung mehrerer physikalischer Größen die geeignet verknüpft werden. Physikalische Größen können sein: Ultraschalllaufzeit, Amplitude des Ultraschallsignals und Umgebungstemperatur. Dazu müssen Korrelationen zwischen dem Zustand des Bauwerks, den Umgebungsbedingungen und den Parametern des gemessenen Ultraschallsignals untersucht werden.
In dieser Arbeit werden die neuartigen Prüfköpfe vorgestellt. Es wird beschrieben, dass sie sich, sowohl in bereits errichtete Betonbauwerke als auch in der Konstruktion befindliche, einbauen lassen. Experimentell wird gezeigt, dass die Prüfköpfe in mehreren Ebenen eingebettet sein können da ihre Abstrahlcharakteristik im Beton nahezu ungerichtet ist. Die Mittenfrequenz von rund 62 kHz ermöglicht Abstände, je nach Betonart und SRV, von mindestens 3 m zwischen Prüfköpfen die als Sender und Empfänger arbeiten. Die Empfindlichkeit der eingebetteten Prüfköpfe gegenüber Veränderungen im Beton wird an Hand von zwei Laborexperimenten gezeigt, einem Drei-Punkt-Biegeversuch und einem Versuch zur Erzeugung von Frost-Tau-Wechsel Schäden. Die Ergebnisse werden mit anderen zerstörungsfreien Prüfverfahren verglichen. Es zeigt sich, dass die Prüfköpfe durch die Anwendung empfindlicher Auswertemethoden, auftretende Risse im Beton detektieren, bevor diese eine Gefahr für das Bauwerk darstellen. Abschließend werden Beispiele von Installation der neuartigen Ultraschallprüfköpfe in realen Bauteilen, zwei Brücken und einem Fundament, gezeigt und basierend auf dort gewonnenen ersten Erfahrungen ein Konzept für die Umsetzung einer Langzeitüberwachung aufgestellt.
Large areas in the humid tropics are currently undergoing land-use change. The decrease of tropical rainforest, which is felled for land clearing and timber production, is countered by increasing areas of tree plantations and secondary forests. These changes are known to affect the regional water cycle as a result of plant-specific water demand and by influencing key soil properties which determine hydrological flow paths. One of these key properties sensitive to land-use change is the saturated hydraulic conductivity (Ks) as it governs vertical percolation of water within the soil profile. Low values of Ks in a certain soil depth can form an impeding layer and lead to perched water tables and the development of predominantly lateral flow paths such as overland flow. These processes can induce nutrient redistribution, erosion and soil degradation and thus affect ecosystem services and human livelihoods. Due to its sensitivity to land-use change, Ks is commonly used to assess the associated changes in hydrological flow paths. The objective of this dissertation was to assess the effect of land-use change on hydrological flow paths by analysing Ks as indicator variable. Sources of Ks variability, their implications for Ks monitoring and the relationship between Ks and near-surface hydrological flow paths in the context of land-use change were studied. The research area was located in central Panama, a country widely experiencing the abovementioned changes in land use. Ks is dependent on both static, soil-inherent properties such as particle size and clay mineralogy and dynamic, land use-dependent properties such as organic carbon content. By conducting a pair of studies with one of these influences held constant in each, the importance of static and dynamic properties for Ks was assessed. Applying a space-for-time approach to sample Ks under secondary forests of different age classes on comparable soils, a recovery of Ks from the former pasture use was shown to require more than eight years. The process was limited to the 0−6 cm sampling depth and showed large variability among replicates. A wavelet analysis of a Ks transect crossing different soil map units under comparable land cover, old-growth tropical rainforest, showed large small-scale variability, which was attributed to biotic influences, as well as a possible but non-conclusive influence of soil types. The two results highlight the importance of dynamic, land use-dependent influences on Ks. Monitoring studies can help to quantify land use-induced change of Ks, but there is a variety of sampling designs which differ in efficiency of estimating mean Ks. A comparative study of four designs and their suitability for Ks monitoring is used to give recommendations about designing a Ks monitoring scheme. Quantifying changes in spatial means of Ks for small catchments with a rotational stratified sampling design did not prove to be more efficient than Simple Random Sampling. The lack of large-scale spatial structure prevented benefits of stratification, and large small-scale variability resulting from local biotic processes and artificial effects of destructive sampling caused a lack of temporal consistency in the re-sampling of locations, which is part of the rotational design. The relationship between Ks and near-surface hydrological flow paths is of critical importance when assessing the consequences of land-use change in the humid tropics. The last part of this dissertation aimed at disclosing spatial relationships between Ks and overland flow as influenced by different land cover types. The effects of Ks on overland-flow generation were spatially variable, different between planar plots and incised flowlines and strongly influenced by land-cover characteristics. A simple comparison of Ks values and rainfall intensities was insufficient to describe the observed pattern of overland flow. Likewise, event flow in the stream was apparently not directly related to overland flow response patterns within the catchments. The study emphasises the importance of combining pedological, hydrological, meteorological and botanical measurements to comprehensively understand the land use-driven change in hydrological flow paths. In summary, Ks proved to be a suitable parameter for assessing the influence of land-use change on soils and hydrological processes. The results illustrated the importance of land cover and spatial variability of Ks for decisions on sampling designs and for interpreting overland-flow generation. As relationships between Ks and overland flow were shown to be complex and dependent on land cover, an interdisciplinary approach is required to comprehensively understand the effects of land-use change on soils and near-surface hydrological flow paths in the humid tropics.
This thesis presents new approaches of SAR methods and their application to tectonically active systems and related surface deformation. With 3 publications two case studies are presented:
(1) The coseismic deformation related to the Nura earthquake (5th October 2008, magnitude Mw 6.6) at the eastern termination of the intramontane Alai valley. Located between the southern Tien Shan and the northern Pamir the coseismic surface displacements are analysed using SAR (Synthetic Aperture RADAR) data. The results show clear gradients in the vertical and horizontal directions along a complex pattern of surface ruptures and active faults. To integrate and to interpret these observations in the context of the regional active tectonics a SAR data analysis is complemented with seismological data and geological field observations. The main moment release of the Nura earthquake appears to be on the Pamir Frontal thrust, while the main surface displacements and surface rupture occurred in the footwall and along of the NE–SW striking Irkeshtam fault. With InSAR data from ascending and descending satellite tracks along with pixel offset measurements the Nura earthquake source is modelled as a segmented rupture. One fault segment corresponds to high-angle brittle faulting at the Pamir Frontal thrust and two more fault segments show moderate-angle and low-friction thrusting at the Irkeshtam fault. The integrated analysis of the coseismic deformation argues for a rupture segmentation and strain partitioning associated to the earthquake. It possibly activated an orogenic wedge in the easternmost segment of the Pamir-Alai collision zone. Further, the style of the segmentation may be associated with the presence of Paleogene evaporites.
(2) The second focus is put on slope instabilities and consequent landslides in the area of prominent topographic transition between the Fergana basin and high-relief Alai range. The Alai range constitutes an active orogenic wedge of the Pamir – Tien Shan collision zone that described as a progressively northward propagating fold-and-thrust belt. The interferometric analysis of ALOS/PALSAR radar data integrates a period of 4 years (2007-2010) based on the Small Baseline Subset (SBAS) time-series technique to assess surface deformation with millimeter surface change accuracy. 118 interferograms are analyzed to observe spatially-continuous movements with downslope velocities up to 71 mm/yr. The obtained rates indicate slow movement of the deep-seated landslides during the observation time. We correlated these movements with precipitation and seismic records. The results suggest that the deformation peaks correlate with rainfall in the 3 preceding months and with one earthquake event. In the next step, to understand the spatial pattern of landslide processes, the tectonic morphologic and lithologic settings are combined with the patterns of surface deformation. We demonstrate that the lithological and tectonic structural patterns are the main controlling factors for landslide occurrence and surface deformation magnitudes. Furthermore active contractional deformation in the front of the orogenic wedge is the main mechanism to sustain relief. Some of the slower but continuously moving slope instabilities are directly related to tectonically active faults and unconsolidated young Quaternary syn-orogenic sedimentary sequences. The InSAR observed slow moving landslides represent active deep-seated gravitational slope deformation phenomena which is first time observed in the Tien Shan mountains. Our approach offers a new combination of InSAR techniques and tectonic aspects to localize and understand enhanced slope instabilities in tectonically active mountain fronts in the Kyrgyz Tien Shan.
The formation and breaching of natural dammed lakes have formed the landscapes, especially in seismically active high-mountain regions. Dammed lakes pose both, potential water resources, and hazard in case of dam breaching. Central Asia has mostly arid and semi-arid climates. Rock glaciers already store more water than ice-glaciers in some semi-arid regions of the world, but their distribution and advance mechanisms are still under debate in recent research. Their impact on the water availability in Central Asia will likely increase as temperatures rise and glaciers diminish.
This thesis provides insight to the relative age distribution of selected Kyrgyz and Kazakh rock glaciers and their single lobes derived from lichenometric dating. The size of roughly 8000 different lichen specimens was used to approximate an exposure age of the underlying debris surface. We showed that rock-glacier movement differs signifcantly on small scales. This has several implications for climatic inferences from rock glaciers. First, reactivation of their lobes does not necessarily point to climatic changes, or at least at out-of-equilibrium conditions. Second, the elevations of rock-glacier toes can no longer be considered as general indicators of the limit of sporadic mountain permafrost as they have been used traditionally.
In the mountainous and seismically active region of Central Asia, natural dams, besides rock glaciers, also play a key role in controlling water and sediment infux into river valleys. However, rock glaciers advancing into valleys seem to be capable of infuencing the stream network, to dam rivers, or to impound lakes. This influence has not previously been addressed. We quantitatively explored these controls using a new inventory of 1300 Central Asian rock glaciers. Elevation, potential incoming solar radiation, and the size of rock glaciers and their feeder basins played key roles in predicting dam appearance. Bayesian techniques were used to credibly distinguish between lichen sizes on rock glaciers and their lobes, and to find those parameters of a rock-glacier system that are most credibly expressing the potential to build natural dams.
To place these studies in the region's history of natural dams, a combination of dating of former lake levels and outburst flood modelling addresses the history and possible outburst flood hypotheses of the second largest mountain lake of the world, Issyk Kul in Kyrgyzstan. Megafoods from breached earthen or glacial dams were found to be a likely explanation for some of the lake's highly fluctuating water levels. However, our detailed analysis of candidate lake sediments and outburst-flood deposits also showed that more localised dam breaks to the west of Issyk Kul could have left similar geomorphic and sedimentary evidence in this Central Asian mountain landscape. We thus caution against readily invoking megafloods as the main cause of lake-level drops of Issyk Kul. In summary, this thesis addresses some new pathways for studying rock glaciers and natural dams with several practical implications for studies on mountain permafrost and natural hazards.
Earthquakes form by sudden brittle failure of rock mostly as shear ruptures along a rupture plane. Beside this, mechanisms other than pure shearing have been observed for some earthquakes mainly in volcanic areas. Possible explanations include complex rupture geometries and tensile earthquakes. Tensile earthquakes occur by opening or closure of cracks during rupturing. They are likely to be often connected with fluids that cause pressure changes in the pore space of rocks leading to earthquake triggering. Tensile components have been reported for swarm earthquakes in West Bohemia in 2000. The aim and subject of this work is an assessment and the accurate determination of such tensile components for earthquakes in anisotropic media. Currently used standard techniques for the retrieval of earthquake source mechanisms assume isotropic rock properties. By means of moment tensors, equivalent forces acting at the source are used to explain the radiated wavefield. Conversely, seismic anisotropy, i.e. directional dependence of elastic properties, has been observed in the earth's crust and mantle such as in West Bohemia. In comparison to isotropy, anisotropy causes modifications in wave amplitudes and shear-wave splitting. In this work, effects of seismic anisotropy on true or apparent tensile source components of earthquakes are investigated. In addition, earthquake source parameters are determined considering anisotropy. It is shown that moment tensors and radiation patterns due to shear sources in anisotropic media may be similar to those of tensile sources in isotropic media. In contrast, similarities between tensile earthquakes in anisotropic rocks and shear sources in isotropic media may exist. As a consequence, the interpretation of tensile source components is ambiguous. The effects that are due to anisotropy depend on the orientation of the earthquake source and the degree of anisotropy. The moment of an earthquake is also influenced by anisotropy. The orientation of fault planes can be reliably determined even if isotropy instead of anisotropy is assumed and if the spectra of the compressional waves are used. Greater difficulties may arise when the spectra of split shear waves are additionally included. Retrieved moment tensors show systematic artefacts. Observed tensile source components determined for events in West Bohemia in 1997 can only partly be attributed to the effects of moderate anisotropy. Furthermore, moment tensors determined earlier for earthquakes induced at the German Continental Deep Drilling Program (KTB), Bavaria, were reinterpreted under assumptions of anisotropic rock properties near the borehole. The events can be consistently identified as shear sources, although their moment tensors comprise tensile components that are considered to be apparent. These results emphasise the necessity to consider anisotropy to uniquely determine tensile source parameters. Therefore, a new inversion algorithm has been developed, tested, and successfully applied to 112 earthquakes that occurred during the most recent intense swarm episode in West Bohemia in 2000 at the German-Czech border. Their source mechanisms have been retrieved using isotropic and anisotropic velocity models. Determined local magnitudes are in the range between 1.6 and 3.2. Fault-plane solutions are similar to each other and characterised by left-lateral faulting on steeply dipping, roughly North-South oriented rupture planes. Their dip angles decrease above a depth of about 8.4km. Tensile source components indicating positive volume changes are found for more than 60% of the considered earthquakes. Their size depends on source time and location. They are significant at the beginning of the swarm and at depths below 8.4km but they decrease in importance later in the course of the swarm. Determined principle stress axes include P axes striking Northeast and Taxes striking Southeast. They resemble those found earlier in Central Europe. However, depth-dependence in plunge is observed. Plunge angles of the P axes decrease gradually from 50° towards shallow angles with increasing depth. In contrast, the plunge angles of the T axes change rapidly from about 8° above a depth of 8.4km to 21° below this depth. By this thesis, spatial and temporal variations in tensile source components and stress conditions have been reported for the first time for swarm earthquakes in West Bohemia in 2000. They also persist, when anisotropy is assumed and can be explained by intrusion of fluids into the opened cracks during tensile faulting.
Modern anthropogenic forcing of atmospheric chemistry poses the question of how the Earth System will respond as thousands of gigatons of greenhouse gas are rapidly added to the atmosphere. A similar, albeit nonanthropogenic, situation occurred during the early Paleogene, when catastrophic release of carbon to the atmosphere triggered abrupt increase in global temperatures. The best documented of these events is the Paleocene-Eocene Thermal Maximum (PETM, ~55 Ma) when the magnitude of carbon addition to the oceans and atmosphere was similar to those expected for the future. This event initiated global warming, changes in hydrological cycles, biotic extinction and migrations. A recently proposed hypothesis concerning changes in marine ecosystems suggests that this global warming strongly influenced the shallow-water biosphere, triggering extinctions and turnover in the Larger Foraminifera (LF) community and the demise of corals. The successions from the Adriatic Carbonate Platform (SW Slovenia) represent an ideal location to test the hypothesis of a possible causal link between the PETM and evolution of shallow-water organisms because they record continuous sedimentation from the Late Paleocene to the Early Eocene and are characterized by a rich biota, especially LF, fundamental for detailed biostratigraphic studies. In order to reconstruct paleoenvironmental conditions during deposition, I focused on sedimentological analysis and paleoecological study of benthic assemblages. During the Late Paleocene-earliest Eocene, sedimentation occurred on a shallow-water carbonate ramp system characterized by enhanced nutrient levels. LF represent the common constituent of the benthic assemblages that thrived in this setting throughout the Late Paleocene to the Early Eocene. With detailed biostratigraphic and chemostratigraphic analyses documenting the most complete record to date available for the PETM event in a shallow-water marine environment, I correlated chemostratigraphically for the first time the evolution of LF with the δ¹³C curves. This correlation demonstrated that no major turnover in the LF communities occurred synchronous with the PETM; thus the evolution of LF was mainly controlled by endogenous biotic forces. The study of Late Thanetian metric-sized microbialite-coral mounds which developed in the middle part of the ramp, documented the first Cenozoic occurrence of microbially-cemented mounds. The development of these mounds, with temporary dominance of microbial communities over corals, suggest environmentally-triggered “phase shifts” related to frequent fluctuations of nutrient/turbidity levels during recurrent wet phases which preceding the extreme greenhouse conditions of the PETM. The paleoecological study of the coral community in the microbialites-coral mounds, the study of corals from Early Eocene platform from SW France, and a critical, extensive literature research of Late Paleocene – Early Eocene coral occurrences from the Tethys, the Atlantic, the Caribbean realms suggested that these corals types, even if not forming extensive reefs, are common in the biofacies as small isolated colonies, piles of rubble or small patch-reefs. These corals might have developed ‘alternative’ life strategies to cope with harsh conditions (high/fluctuating nutrients/turbidity, extreme temperatures, perturbation of aragonite saturation state) during the greenhouse times of the early Paleogene, representing a good fossil analogue to modern corals thriving close to their thresholds for survival. These results demonstrate the complexity of the biological responses to extreme conditions, not only in terms of temperature but also nutrient supply, physical disturbance and their temporal variability and oscillating character.
The Arctic nearshore zone plays a key role in the carbon cycle. Organic-rich sediments get eroded off permafrost affected coastlines and can be directly transferred to the nearshore zone. Permafrost in the Arctic stores a high amount of organic matter and is vulnerable to thermo-erosion, which is expected to increase due to climate change. This will likely result in higher sediment loads in nearshore waters and has the potential to alter local ecosystems by limiting light transmission into the water column, thus limiting primary production to the top-most part of it, and increasing nutrient export from coastal erosion. Greater organic matter input could result in the release of greenhouse gases to the atmosphere. Climate change also acts upon the fluvial system, leading to greater discharge to the nearshore zone. It leads to decreasing sea-ice cover as well, which will both increase wave energy and lengthen the open-water season. Yet, knowledge on these processes and the resulting impact on the nearshore zone is scarce, because access to and instrument deployment in the nearshore zone is challenging.
Remote sensing can alleviate these issues in providing rapid data delivery in otherwise non-accessible areas. However, the waters in the Arctic nearshore zone are optically complex, with multiple influencing factors, such as organic rich suspended sediments, colored dissolved organic matter (cDOM), and phytoplankton. The goal of this dissertation was to use remotely sensed imagery to monitor processes related to turbidity caused by suspended sediments in the Arctic nearshore zone. In-situ measurements of water-leaving reflectance and surface water turbidity were used to calibrate a semi-empirical algorithm which relates turbidity from satellite imagery. Based on this algorithm and ancillary ocean and climate variables, the mechanisms underpinning nearshore turbidity in the Arctic were identified at a resolution not achieved before.
The calibration of the Arctic Nearshore Turbidity Algorithm (ANTA) was based on in-situ measurements from the coastal and inner-shelf waters around Herschel Island Qikiqtaruk (HIQ) in the western Canadian Arctic from the summer seasons 2018 and 2019. It performed better than existing algorithms, developed for global applications, in relating turbidity from remotely sensed imagery. These existing algorithms were lacking validation data from permafrost affected waters, and were thus not able to reflect the complexity of Arctic nearshore waters. The ANTA has a higher sensitivity towards the lowest turbidity values, which is an asset for identifying sediment pathways in the nearshore zone. Its transferability to areas beyond HIQ was successfully demonstrated using turbidity measurements matching satellite image recordings from Adventfjorden, Svalbard. The ANTA is a powerful tool that provides robust turbidity estimations in a variety of Arctic nearshore environments.
Drivers of nearshore turbidity in the Arctic were analyzed by combining ANTA results from the summer season 2019 from HIQ with ocean and climate variables obtained from the weather station at HIQ, the ERA5 reanalysis database, and the Mackenzie River discharge. ERA5 reanalysis data were obtained as domain averages over the Canadian Beaufort Shelf. Nearshore turbidity was linearly correlated to wind speed, significant wave height and wave period. Interestingly, nearshore turbidity was only correlated to wind speed at the shelf, but not to the in-situ measurements from the weather station at HIQ. This shows that nearshore turbidity, albeit being of limited spatial extent, gets influenced by the weather conditions multiple kilometers away, rather than in its direct vicinity. The large influence of wave energy on nearshore turbidity indicates that freshly eroded material off the coast is a major contributor to the nearshore sediment load. This contrasts results from the temperate and tropical oceans, where tides and currents are the major drivers of nearshore turbidity. The Mackenzie River discharge was not identified as a driver of nearshore turbidity in 2019, however, the analysis of 30 years of Landsat archive imagery from 1986 to 2016 suggests a direct link between the prevailing wind direction, which heavily influences the Mackenzie River plume extent, and nearshore turbidity around HIQ. This discrepancy could be caused by the abnormal discharge behavior of the Mackenzie River in 2019.
This dissertation has substantially advanced the understanding of suspended sediment processes in the Arctic nearshore zone and provided new monitoring tools for future studies. The presented results will help to understand the role of the Arctic nearshore zone in the carbon cycle under a changing climate.
Geomorphology seeks to characterize the forms, rates, and magnitudes of sediment and water transport that sculpt landscapes. This is generally referred to as earth surface processes, which incorporates the influence of biologic (e.g., vegetation), climatic (e.g., rainfall), and tectonic (e.g., mountain uplift) factors in dictating the transport of water and eroded material. In mountains, high relief and steep slopes combine with strong gradients in rainfall and vegetation to create dynamic expressions of earth surface processes. This same rugged topography presents challenges in data collection and process measurement, where traditional techniques involving detailed observations or physical sampling are difficult to apply at the scale of entire catchments. Herein lies the utility of remote sensing. Remote sensing is defined as any measurement that does not disturb the natural environment, typically via acquisition of images in the visible- to radio-wavelength range of the electromagnetic spectrum. Remote sensing is an especially attractive option for measuring earth surface processes, because large areal measurements can be acquired at much lower cost and effort than traditional methods. These measurements cover not only topographic form, but also climatic and environmental metrics, which are all intertwined in the study of earth surface processes. This dissertation uses remote sensing data ranging from handheld camera-based photo surveying to spaceborne satellite observations to measure the expressions, rates, and magnitudes of earth surface processes in high-mountain catchments of the Eastern Central Andes in Northwest Argentina. This work probes the limits and caveats of remote sensing data and techniques applied to geomorphic research questions, and presents important progress at this disciplinary intersection.
Natural extreme events are an integral part of nature on planet earth. Usually these events are only considered hazardous to humans, in case they are exposed. In this case, however, natural hazards can have devastating impacts on human societies. Especially hydro-meteorological hazards have a high damage potential in form of e.g. riverine and pluvial floods, winter storms, hurricanes and tornadoes, which can occur all over the globe. Along with an increasingly warm climate also an increase in extreme weather which potentially triggers natural hazards can be expected. Yet, not only changing natural systems, but also changing societal systems contribute to an increasing risk associated with these hazards. These can comprise increasing exposure and possibly also increasing vulnerability to the impacts of natural events. Thus, appropriate risk management is required to adapt all parts of society to existing and upcoming risks at various spatial scales. One essential part of risk management is the risk assessment including the estimation of the economic impacts. However, reliable methods for the estimation of economic impacts due to hydro-meteorological hazards are still missing. Therefore, this thesis deals with the question of how the reliability of hazard damage estimates can be improved, represented and propagated across all spatial scales. This question is investigated using the specific example of economic impacts to companies as a result of riverine floods in Germany.
Flood damage models aim to describe the damage processes during a given flood event. In other words they describe the vulnerability of a specific object to a flood. The models can be based on empirical data sets collected after flood events. In this thesis tree-based models trained with survey data are used for the estimation of direct economic flood impacts on the objects. It is found that these machine learning models, in conjunction with increasing sizes of data sets used to derive the models, outperform state-of-the-art damage models. However, despite the performance improvements induced by using multiple variables and more data points, large prediction errors remain at the object level. The occurrence of the high errors was explained by a further investigation using distributions derived from tree-based models. The investigation showed that direct economic impacts to individual objects cannot be modeled by a normal distribution. Yet, most state-of-the-art approaches assume a normal distribution and take mean values as point estimators. Subsequently, the predictions are unlikely values within the distributions resulting in high errors. At larger spatial scales more objects are considered for the damage estimation. This leads to a better fit of the damage estimates to a normal distribution. Consequently, also the performance of the point estimators get better, although large errors can still occur due to the variance of the normal distribution. It is recommended to use distributions instead of point estimates in order to represent the reliability of damage estimates.
In addition current approaches also mostly ignore the uncertainty associated with the characteristics of the hazard and the exposed objects. For a given flood event e.g. the estimation of the water level at a certain building is prone to uncertainties. Current approaches define exposed objects mostly by the use of land use data sets. These data sets often show inconsistencies, which introduce additional uncertainties. Furthermore, state-of-the-art approaches also imply problems of missing consistency when predicting the damage at different spatial scales. This is due to the use of different types of exposure data sets for model derivation and application. In order to face these issues a novel object-based method was developed in this thesis. The method enables a seamless estimation of hydro-meteorological hazard damage across spatial scales including uncertainty quantification. The application and validation of the method resulted in plausible estimations at all spatial scales without overestimating the uncertainty.
Mainly newly available data sets containing individual buildings make the application of the method possible as they allow for the identification of flood affected objects by overlaying the data sets with water masks. However, the identification of affected objects with two different water masks revealed huge differences in the number of identified objects. Thus, more effort is needed for their identification, since the number of objects affected determines the order of magnitude of the economic flood impacts to a large extent.
In general the method represents the uncertainties associated with the three components of risk namely hazard, exposure and vulnerability, in form of probability distributions. The object-based approach enables a consistent propagation of these uncertainties in space. Aside from the propagation of damage estimates and their uncertainties across spatial scales, a propagation between models estimating direct and indirect economic impacts was demonstrated. This enables the inclusion of uncertainties associated with the direct economic impacts within the estimation of the indirect economic impacts. Consequently, the modeling procedure facilitates the representation of the reliability of estimated total economic impacts. The representation of the estimates' reliability prevents reasoning based on a false certainty, which might be attributed to point estimates. Therefore, the developed approach facilitates a meaningful flood risk management and adaptation planning.
The successful post-event application and the representation of the uncertainties qualifies the method also for the use for future risk assessments. Thus, the developed method enables the representation of the assumptions made for the future risk assessments, which is crucial information for future risk management. This is an important step forward, since the representation of reliability associated with all components of risk is currently lacking in all state-of-the-art methods assessing future risk.
In conclusion, the use of object-based methods giving results in the form of distributions instead of point estimations is recommended. The improvement of the model performance by the means of multi-variable models and additional data points is possible, but small. Uncertainties associated with all components of damage estimation should be included and represented within the results. Furthermore, the findings of the thesis suggest that, at larger scales, the influence of the uncertainty associated with the vulnerability is smaller than those associated with the hazard and exposure. This leads to the conclusion that for an increased reliability of flood damage estimations and risk assessments, the improvement and active inclusion of hazard and exposure, including their uncertainties, is needed in addition to the improvements of the models describing the vulnerability of the objects.
Adjustment of empirically derived ground motion prediction equations (GMPEs), from a data- rich region/site where they have been derived to a data-poor region/site, is one of the major challenges associated with the current practice of seismic hazard analysis. Due to the fre- quent use in engineering design practices the GMPEs are often derived for response spectral ordinates (e.g., spectral acceleration) of a single degree of freedom (SDOF) oscillator. The functional forms of such GMPEs are based upon the concepts borrowed from the Fourier spectral representation of ground motion. This assumption regarding the validity of Fourier spectral concepts in the response spectral domain can lead to consequences which cannot be explained physically.
In this thesis, firstly results from an investigation that explores the relationship between Fourier and response spectra, and implications of this relationship on the adjustment issues of GMPEs, are presented. The relationship between the Fourier and response spectra is explored by using random vibration theory (RVT), a framework that has been extensively used in earthquake engineering, for instance within the stochastic simulation framework and in the site response analysis. For a 5% damped SDOF oscillator the RVT perspective of response spectra reveals that no one-to-one correspondence exists between Fourier and response spectral ordinates except in a limited range (i.e., below the peak of the response spectra) of oscillator frequencies. The high oscillator frequency response spectral ordinates are dominated by the contributions from the Fourier spectral ordinates that correspond to the frequencies well below a selected oscillator frequency. The peak ground acceleration (PGA) is found to be related with the integral over the entire Fourier spectrum of ground motion which is in contrast to the popularly held perception that PGA is a high-frequency phenomenon of ground motion.
This thesis presents a new perspective for developing a response spectral GMPE that takes the relationship between Fourier and response spectra into account. Essentially, this frame- work involves a two-step method for deriving a response spectral GMPE: in the first step two empirical models for the FAS and for a predetermined estimate of duration of ground motion are derived, in the next step, predictions from the two models are combined within the same RVT framework to obtain the response spectral ordinates. In addition to that, a stochastic model based scheme for extrapolating the individual acceleration spectra beyond the useable frequency limits is also presented. To that end, recorded acceleration traces were inverted to obtain the stochastic model parameters that allow making consistent extrapola- tion in individual (acceleration) Fourier spectra. Moreover an empirical model, for a dura- tion measure that is consistent within the RVT framework, is derived. As a next step, an oscillator-frequency-dependent empirical duration model is derived that allows obtaining the most reliable estimates of response spectral ordinates. The framework of deriving the response spectral GMPE presented herein becomes a self-adjusting model with the inclusion of stress parameter (∆σ) and kappa (κ0) as the predictor variables in the two empirical models. The entire analysis of developing the response spectral GMPE is performed on recently compiled RESORCE-2012 database that contains recordings made from Europe, the Mediterranean and the Middle East. The presented GMPE for response spectral ordinates should be considered valid in the magnitude range of 4 ≤ MW ≤ 7.6 at distances ≤ 200 km.
To find out the future of nowadays reef ecosystem turnover under the environmental stresses such as global warming and ocean acidification, analogue studies from the geologic past are needed. As a critical time of reef ecosystem innovation, the Permian-Triassic transition witnessed the most severe demise of Phanerozoic reef builders, and the establishment of modern style symbiotic relationships within the reef-building organisms. Being the initial stage of this transition, the Middle Permian (Capitanian) mass extinction coursed a reef eclipse in the early Late Permian, which lead to a gap of understanding in the post-extinction Wuchiapingian reef ecosystem, shortly before the radiation of Changhsingian reefs. Here, this thesis presents detailed biostratigraphic, sedimentological, and palaeoecological studies of the Wuchiapingian reef recovery following the Middle Permian (Capitanian) mass extinction, on the only recorded Wuchiapingian reef setting, outcropping in South China at the Tieqiao section.
Conodont biostratigraphic zonations were revised from the Early Permian Artinskian to the Late Permian Wuchiapingian in the Tieqiao section. Twenty main and seven subordinate conodont zones are determined at Tieqiao section including two conodont zone below and above the Tieqiao reef complex. The age of Tieqiao reef was constrained as early to middle Wuchiapingian.
After constraining the reef age, detailed two-dimensional outcrop mapping combined with lithofacies study were carried out on the Wuchiapingian Tieqiao Section to investigate the reef growth pattern stratigraphically as well as the lateral changes of reef geometry on the outcrop scale. Semi-quantitative studies of the reef-building organisms were used to find out their evolution pattern within the reef recovery. Six reef growth cycles were determined within six transgressive-regressive cycles in the Tieqiao section. The reefs developed within the upper part of each regressive phase and were dominated by different biotas. The timing of initial reef recovery after the Middle Permian (Capitanian) mass extinction was updated to the Clarkina leveni conodont zone, which is earlier than previous understanding. Metazoans such as sponges were not the major components of the Wuchiapingian reefs until the 5th and 6th cycles. So, the recovery of metazoan reef ecosystem after the Middle Permian (Capitanian) mass extinction was obviously delayed. In addition, although the importance of metazoan reef builders such as sponges did increase following the recovery process, encrusting organisms such as Archaeolithoporella and Tubiphytes, combined with microbial carbonate precipitation, still played significant roles to the reef building process and reef recovery after the mass extinction.
Based on the results from outcrop mapping and sedimentological studies, quantitative composition analysis of the Tieqiao reef complex were applied on selected thin sections to further investigate the functioning of reef building components and the reef evolution after the Middle Permian (Capitanian) mass extinction. Data sets of skeletal grains and whole rock components were analyzed. The results show eleven biocommunity clusters/eight rock composition clusters dominated by different skeletal grains/rock components. Sponges, Archaeolithoporella and Tubiphytes were the most ecologically important components within the Wuchiapingian Tieqiao reef, while the clotted micrites and syndepositional cements are the additional important rock components for reef cores. The sponges were important within the whole reef recovery. Tubiphytes were broadly distributed in different environments and played a key-role in the initial reef communities. Archaeolithoporella concentrated in the shallower part of reef cycles (i.e., the upper part of reef core) and was functionally significant for the enlargement of reef volume.
In general, the reef recovery after the Middle Permian (Capitanian) mass extinction has some similarities with the reef recovery following the end-Permian mass extinction. It shows a delayed recovery of metazoan reefs and a stepwise recovery pattern that was controlled by both ecological and environmental factors. The importance of encrusting organisms and microbial carbonates are also similar to most of the other post-extinction reef ecosystems. These findings can be instructive to extend our understanding of the reef ecosystem evolution under environmental perturbation or stresses.
The East African Rift System (EARS) is a significant example of active tectonics, which provides opportunities to examine the stages of continental faulting and landscape evolution. The southwest extension of the EARS is one of the most significant examples of active tectonics nowadays, however, seismotectonic research in the area has been scarce, despite the fundamental importance of neotectonics. Our first study area is located between the Northern Province of Zambia and the southeastern Katanga Province of the Democratic Republic of Congo. Lakes Mweru and Mweru Wantipa are part of the southwest extension of the EARS. Fault analysis reveals that, since the Miocene, movements along the active Mweru-Mweru Wantipa Fault System (MMFS) have been largely responsible for the reorganization of the landscape and the drainage patterns across the southwestern branch of the EARS. To investigate the spatial and temporal patterns of fluvial-lacustrine landscape development, we determined in-situ cosmogenic 10Be and 26Al in a total of twenty-six quartzitic bedrock samples that were collected from knickpoints across the Mporokoso Plateau (south of Lake Mweru) and the eastern part of the Kundelungu Plateau (north of Lake Mweru). Samples from the Mporokoso Plateau and close to the MMFS provide evidence of temporary burial. By contrast, surfaces located far from the MMFS appear to have remained uncovered since their initial exposure as they show consistent 10Be and 26Al exposure ages ranging up to ~830 ka. Reconciliation of the observed burial patterns with morphotectonic and stratigraphic analysis reveals the existence of an extensive paleo-lake during the Pleistocene. Through hypsometric analyses of the dated knickpoints, the potential maximum water level of the paleo-lake is constrained to ~1200 m asl (present lake lavel: 917 m asl). High denudation rates (up to ~40 mm ka-1) along the eastern Kundelungu Plateau suggest that footwall uplift, resulting from normal faulting, caused river incision, possibly controlling paleo-lake drainage. The lake level was reduced gradually reaching its current level at ~350 ka.
Parallel to the MMFS in the north, the Upemba Fault System (UFS) extends across the southeastern Katanga Province of the Democratic Republic of Congo. This part of our research is focused on the geomorphological behavior of the Kiubo Waterfalls. The waterfalls are the currently active knickpoint of the Lufira River, which flows into the Upemba Depression. Eleven bedrock samples along the Lufira River and its tributary stream, Luvilombo River, were collected. In-situ cosmogenic 10Be and 26Al were used in order to constrain the K constant of the Stream Power Law equation. Constraining the K constant allowed us to calculate the knickpoint retreat rate of the Kiubo Waterfalls at ~0.096 m a-1. Combining the calculated retreat rate of the knickpoint with DNA sequencing from fish populations, we managed to present extrapolation models and estimate the location of the onset of the Kiubo Waterfalls, revealing its connection to the seismicity of the UFS.
Spatial and temporal temperature and moisture patterns across the Tibetan Plateau are very complex. The onset and magnitude of the Holocene climate optimum in the Asian monsoon realm, in particular, is a subject of considerable debate as this time period is often used as an analogue for recent global warming. In the light of contradictory inferences regarding past climate and environmental change on the Tibetan Plateau, I have attempted to explain mismatches in the timing and magnitude of change. Therefore, I analysed the temporal variation of fossil pollen and diatom spectra and the geochemical record from palaeo-ecological records covering different time scales (late Quaternary and the last 200 years) from two core regions in the NE and SE Tibetan Plateau. For interpretation purposes I combined my data with other available palaeo-ecological data to set up corresponding aquatic and terrestrial proxy data sets of two lake pairs and two sets of sites. I focused on the direct comparison of proxies representing lacustrine response to climate signals (e.g., diatoms, ostracods, geochemical record) and proxies representing changes in the terrestrial environment (i.e., terrestrial pollen), in order to asses whether the lake and its catchments respond at similar times and magnitudes to environmental changes. Therefore, I introduced the established numerical technique procrustes rotation as a new approach in palaeoecology to quantitatively compare raw data of any two sedimentary records of interest in order to assess their degree of concordance. Focusing on the late Quaternary, sediment cores from two lakes (Kuhai Lake 35.3°N; 99.2°E; 4150 m asl; and Koucha Lake 34.0°N; 97.2°E; 4540 m asl) on the semi-arid northeastern Tibetan Plateau were analysed to identify post-glacial vegetation and environmental changes, and to investigate the responses of lake ecosystems to such changes. Based on the pollen record, five major vegetation and climate changes could be identified: (1) A shift from alpine desert to alpine steppe indicates a change from cold, dry conditions to warmer and more moist conditions at 14.8 cal. ka BP, (2) alpine steppe with tundra elements points to conditions of higher effective moisture and a stepwise warming climate at 13.6 cal. ka BP, (3) the appearance of high-alpine meadow vegetation indicates a further change towards increased moisture, but with colder temperatures, at 7.0 cal. ka BP, (4) the reoccurrence of alpine steppe with desert elements suggests a return to a significantly colder and drier phase at 6.3 cal. ka BP, and (5) the establishment of alpine steppe-meadow vegetation indicates a change back to relatively moist conditions at 2.2 cal. ka BP. To place the reconstructed climate inferences from the NE Tibetan Plateau into the context of Holocene moisture evolution across the Tibetan Plateau, I applied a five-scale moisture index and average link clustering to all available continuous pollen and non-pollen palaeoclimate records from the Tibetan Plateau, in an attempt to detect coherent regional and temporal patterns of moisture evolution on the Plateau. However, no common temporal or spatial pattern of moisture evolution during the Holocene could be detected, which can be assigned to the complex responses of different proxies to environmental changes in an already very heterogeneous mountain landscape, where minor differences in elevation can result in marked variations in microenvironments. Focusing on the past 200 years, I analysed the sedimentary records (LC6 Lake 29.5°N, 94.3°E, 4132 m asl; and Wuxu Lake 29.9°N, 101.1°E, 3705 m asl) from the southeastern Tibetan Plateau. I found that despite presumed significant temperature increases over that period, pollen and diatom records from the SE Tibetan Plateau reveal only very subtle changes throughout their profiles. The compositional species turnover investigated over the last 200 years appears relatively low in comparison to the species reorganisations during the Holocene. The results indicate that climatically induced ecological thresholds are not yet crossed, but that human activity has an increasing influence, particularly on the terrestrial ecosystem. Forest clearances and reforestation have not caused forest decline in our study area, but a conversion of natural forests to semi-natural secondary forests. The results from the numerical proxy comparison of the two sets of two pairs of Tibetan lakes indicate that the use of different proxies and the work with palaeo-ecological records from different lake types can cause deviant stories of inferred change. Irrespective of the timescale (Holocene or last 200 years) or region (SE or NE Tibetan Plateau) analysed, the agreement in terms of the direction, timing, and magnitude of change between the corresponding terrestrial data sets is generally better than the match between the corresponding lacustrine data sets, suggesting that lacustrine proxies may partly be influenced by in-lake or local catchment processes whereas the terrestrial proxy reflects a more regional climatic signal. The current disaccord on coherent temporal and spatial climate patterns on the Tibetan Plateau can partly be ascribed to the complexity of proxy response and lake systems on the Tibetan Plateau. Therefore, a multi-proxy, multi-site approach is important in order to gain a reliable climate interpretation for the complex mountain landscape of the Tibetan Plateau.
Reconstructing climate from the Dead Sea sediment record using high-resolution micro-facies analyses
(2015)
The sedimentary record of the Dead Sea is a key archive for reconstructing climate in the eastern Mediterranean region, as it stores the environmental and tectonic history of the Levant for the entire Quaternary. Moreover, the lake is located at the boundary between Mediterranean sub-humid to semi-arid and Saharo-Arabian hyper-arid climates, so that even small shifts in atmospheric circulation are sensitively recorded in the sediments. This DFG-funded doctoral project was carried out within the ICDP Dead Sea Deep Drilling Project (DSDDP) that intended to gain the first long, continuous and high-resolution sediment core from the deep Dead Sea basin. The drilling campaign was performed in winter 2010-11 and more than 700 m of sediments were recovered. The main aim of this thesis was (1) to establish the lithostratigraphic framework for the ~455 m long sediment core from the deep Dead Sea basin and (2) to apply high-resolution micro-facies analyses for reconstructing and better understanding climate variability from the Dead Sea sediments.
Addressing the first aim, the sedimentary facies of the ~455 m long deep-basin core 5017-1 were described in great detail and characterised through continuous overview-XRF element scanning and magnetic susceptibility measurements. Three facies groups were classified: (1) the marl facies group, (2) the halite facies group and (3) a group involving different expressions of massive, graded and slumped deposits including coarse clastic detritus. Core 5017-1 encompasses a succession of four main lithological units. Based on first radiocarbon and U-Th ages and correlation of these units to on-shore stratigraphic sections, the record comprises the last ca 220 ka, i.e. the upper part of the Amora Formation (parts of or entire penultimate interglacial and glacial), the last interglacial Samra Fm. (~135-75 ka), the last glacial Lisan Fm. (~75-14 ka) and the Holocene Ze’elim Formation. A major advancement of this record is that, for the first time, also transitional intervals were recovered that are missing in the exposed formations and that can now be studied in great detail.
Micro-facies analyses involve a combination of high-resolution microscopic thin section analysis and µXRF element scanning supported by magnetic susceptibility measurements. This approach allows identifying and characterising micro-facies types, detecting event layers and reconstructing past climate variability with up to seasonal resolution, given that the analysed sediments are annually laminated. Within this thesis, micro-facies analyses, supported by further sedimentological and geochemical analyses (grain size, X-ray diffraction, total organic carbon and calcium carbonate contents) and palynology, were applied for two time intervals:
(1) The early last glacial period ~117-75 ka was investigated focusing on millennial-scale hydroclimatic variations and lake level changes recorded in the sediments. Thereby, distinguishing six different micro-facies types with distinct geochemical and sedimentological characteristics allowed estimating relative lake level and water balance changes of the lake. Comparison of the results to other records in the Mediterranean region suggests a close link of the hydroclimate in the Levant to North Atlantic and Mediterranean climates during the time of the build-up of Northern hemisphere ice sheets during the early last glacial period.
(2) A mostly annually laminated late Holocene section (~3700-1700 cal yr BP) was analysed in unprecedented detail through a multi-proxy, inter-site correlation approach of a shallow-water core (DSEn) and its deep-basin counterpart (5017-1). Within this study, a ca 1500 years comprising time series of erosion and dust deposition events was established and anchored to the absolute time-scale through 14C dating and age modelling. A particular focus of this study was the characterisation of two dry periods, from ~3500 to 3300 and from ~3000 to 2400 cal yr BP, respectively. Thereby, a major outcome was the coincidence of the latter dry period with a period of moist and cold climate in Europe related to a Grand Solar Minimum around 2800 cal yr BP and an increase in flood events despite overall dry conditions in the Dead Sea region during that time. These contrasting climate signatures in Europe and at the Dead Sea were likely linked through complex teleconnections of atmospheric circulation, causing a change in synoptic weather patterns in the eastern Mediterranean.
In summary, within this doctorate the lithostratigraphic framework of a unique long sediment core from the deep Dead Sea basin is established, which serves as a base for any further high-resolution investigations on this core. It is demonstrated in two case studies that micro-facies analyses are an invaluable tool to understand the depositional processes in the Dead Sea and to decipher past climate variability in the Levant on millennial to seasonal time-scales. Hence, this work adds important knowledge helping to establish the deep Dead Sea record as a key climate archive of supra-regional significance.
Modern acquisition of seismic data on receiver networks worldwide produces an increasing amount of continuous wavefield recordings. Hence, in addition to manual data inspection, seismogram interpretation requires new processing utilities for event detection, signal classification and data visualization. Various machine learning algorithms, which can be adapted to seismological problems, have been suggested in the field of pattern recognition. This can be done either by means of supervised learning using manually defined training data or by unsupervised clustering and visualization. The latter allows the recognition of wavefield patterns, such as short-term transients and long-term variations, with a minimum of domain knowledge. Besides classical earthquake seismology, investigations of temporal patterns in seismic data also concern novel approaches such as noise cross-correlation or ambient seismic vibration analysis in general, which have moved into focus within the last decade. In order to find records suitable for the respective approach or simply for quality control, unsupervised preprocessing becomes important and valuable for large data sets. Machine learning techniques require the parametrization of the data using feature vectors. Applied to seismic recordings, wavefield properties have to be computed from the raw seismograms. For an unsupervised approach, all potential wavefield features have to be considered to reduce subjectivity to a minimum. Furthermore, automatic dimensionality reduction, i.e. feature selection, is required in order to decrease computational cost, enhance interpretability and improve discriminative power. This study presents an unsupervised feature selection and learning approach for the discovery, imaging and interpretation of significant temporal patterns in seismic single-station or network recordings. In particular, techniques permitting an intuitive, quickly interpretable and concise overview of available records are suggested. For this purpose, the data is parametrized by real-valued feature vectors for short time windows using standard seismic analysis tools as feature generation methods, such as frequency-wavenumber, polarization, and spectral analysis. The choice of the time window length is dependent on the expected durations of patterns to be recognized or discriminated. We use Self-Organizing Maps (SOMs) for a data-driven feature selection, visualization and clustering procedure, which is particularly suitable for high-dimensional data sets. Using synthetics composed of Rayleigh and Love waves and three different types of real-world data sets, we show the robustness and reliability of our unsupervised learning approach with respect to the effect of algorithm parameters and data set properties. Furthermore, we approve the capability of the clustering and imaging techniques. For all data, we find improved discriminative power of our feature selection procedure compared to feature subsets manually selected from individual wavefield parametrization methods. In particular, enhanced performance is observed compared to the most favorable individual feature generation method, which is found to be the frequency spectrum. The method is applied to regional earthquake records at the European Broadband Network with the aim to define suitable features for earthquake detection and seismic phase classification. For the latter, we find that a combination of spectral and polarization features favor S wave detection at a single receiver. However, SOM-based visualization of phase discrimination shows that clustering applied to the records of two stations only allows onset or P wave detection, respectively. In order to improve the discrimination of S waves on receiver networks, we recommend to consider additionally the temporal context of feature vectors. The application to continuous recordings of seismicity close to an active volcano (Mount Merapi, Java, Indonesia) shows that two typical volcano-seismic events (VTB and Guguran) can be detected and distinguished by clustering. In contrast, so-called MP events cannot be discriminated. Comparable results are obtained for selected features and recognition rates regarding a previously implemented supervised classification system. Finally, we test the reliability of wavefield clustering to improve common ambient vibration analysis methods such as estimation of dispersion curves and horizontal to vertical spectral ratios. It is found, that in general, the identified short- and long-term patterns have no significant impact on those estimates. However, for individual sites, effects of local sources can be identified. Leaving out the corresponding clusters, yields reduced uncertainties or allows for improving estimation of dispersion curves.
Over the past decades, rapid and constant advances have motivated GNSS technology to approach the ability to monitor transient ground motions with mm to cm accuracy in real-time. As a result, the potential of using real-time GNSS for natural hazards prediction and early warning has been exploited intensively in recent years, e.g., landslides and volcanic eruptions monitoring. Of particular note, compared with traditional seismic instruments, GNSS does not saturate or tilt in terms of co-seismic displacement retrieving, which makes it especially valuable for earthquake and earthquake induced tsunami early warning. In this thesis, we focus on the application of real-time GNSS to fast seismic source inversion and tsunami early warning.
Firstly, we present a new approach to get precise co-seismic displacements using cost effective single-frequency receivers. As is well known, with regard to high precision positioning, the main obstacle for single-frequency GPS receiver is ionospheric delay. Considering that over a few minutes, the change of ionospheric delay is almost linear, we constructed a linear model for each satellite to predict ionospheric delay. The effectiveness of this method has been validated by an out-door experiment and 2011 Tohoku event, which confirms feasibility of using dense GPS networks for geo-hazard early warning at an affordable cost.
Secondly, we extended temporal point positioning from GPS-only to GPS/GLONASS and assessed the potential benefits of multi-GNSS for co-seismic displacement determination. Out-door experiments reveal that when observations are conducted in an adversary environment, adding a couple of GLONASS satellites could provide more reliable results. The case study of 2015 Illapel Mw 8.3 earthquake shows that the biases between co-seismic displacements derived from GPS-only and GPS/GLONASS vary from station to station, and could be up to 2 cm in horizontal direction and almost 3 cm in vertical direction. Furthermore, slips inverted from GPS/GLONASS co-seismic displacements using a layered crust structure on a curved plane are shallower and larger for the Illapel event.
Thirdly, we tested different inversion tools and discussed the uncertainties of using real-time GNSS for tsunami early warning. To be exact, centroid moment tensor inversion, uniform slip inversion using a single Okada fault and distributed slip inversion in layered crust on a curved plane were conducted using co-seismic displacements recorded during 2014 Pisagua earthquake. While the inversion results give similar magnitude and the rupture center, there are significant differences in depth, strike, dip and rake angles, which lead to different tsunami propagation scenarios. Even though, resulting tsunami forecasting along the Chilean coast is close to each other for all three models.
Finally, based on the fact that the positioning performance of BDS is now equivalent to GPS in Asia-Pacific area and Manila subduction zone has been identified as a zone of potential tsunami hazard, we suggested a conceptual BDS/GPS network for tsunami early warning in South China Sea. Numerical simulations with two earthquakes (Mw 8.0 and Mw 7.5) and induced tsunamis demonstrate the viability of this network. In addition, the advantage of BDS/GPS over a single GNSS system by source inversion grows with decreasing earthquake magnitudes.
Quantitative Analysen magmatischer Gesteine mittels reflexionsspektroskopischer Infrarot-Messungen
(2004)
Together with the gradual change of mean values, ongoing climate change is projected to increase frequency and amplitude of temperature and precipitation extremes in many regions of Europe. The impacts of such in most cases short term extraordinary climate situations on terrestrial ecosystems are a matter of central interest of recent climate change research, because it can not per se be assumed that known dependencies between climate variables and ecosystems are linearly scalable. So far, yet, there is a high demand for a method to quantify such impacts in terms of simultaneities of event time series.
In the course of this manuscript the new statistical approach of Event Coincidence Analysis (ECA) as well as it's R implementation is introduced, a methodology that allows assessing whether or not two types of event time series exhibit similar sequences of occurrences. Applications of the method are presented, analyzing climate impacts on different temporal and spacial scales: the impact of extraordinary expressions of various climatic variables on tree stem variations (subdaily and local scale), the impact of extreme temperature and precipitation events on the owering time of European shrub species (weekly and country scale), the impact of extreme temperature events on ecosystem health in terms of NDVI (weekly and continental scale) and the impact of El Niño and La Niña events on precipitation anomalies (seasonal and global scale).
The applications presented in this thesis refine already known relationships based on classical methods and also deliver substantial new findings to the scientific community: the widely known positive correlation between flowering time and temperature for example is confirmed to be valid for the tails of the distributions while the widely assumed positive dependency between stem diameter variation and temperature is shown to be not valid for very warm and very cold days. The larger scale investigations underline the sensitivity of anthrogenically shaped landscapes towards temperature extremes in Europe and provide a comprehensive global ENSO impact map for strong precipitation events.
Finally, by publishing the R implementation of the method, this thesis shall enable other researcher to further investigate on similar research questions by using Event Coincidence Analysis.
Rapidly uplifting coastlines are frequently associated with convergent tectonic boundaries, like subduction zones, which are repeatedly breached by giant megathrust earthquakes. The coastal relief along tectonically active realms is shaped by the effect of sea-level variations and heterogeneous patterns of permanent tectonic deformation, which are accumulated through several cycles of megathrust earthquakes. However, the correlation between earthquake deformation patterns and the sustained long-term segmentation of forearcs, particularly in Chile, remains poorly understood. Furthermore, the methods used to estimate permanent deformation from geomorphic markers, like marine terraces, have remained qualitative and are based on unrepeatable methods. This contrasts with the increasing resolution of digital elevation models, such as Light Detection and Ranging (LiDAR) and high-resolution bathymetric surveys.
Throughout this thesis I study permanent deformation in a holistic manner: from the methods to assess deformation rates, to the processes involved in its accumulation. My research focuses particularly on two aspects: Developing methodologies to assess permanent deformation using marine terraces, and comparing permanent deformation with seismic cycle deformation patterns under different spatial scales along the M8.8 Maule earthquake (2010) rupture zone. Two methods are developed to determine deformation rates from wave-built and wave-cut terraces respectively. I selected an archetypal example of a wave-built terrace at Santa Maria Island studying its stratigraphy and recognizing sequences of reoccupation events tied with eleven radiocarbon sample ages (14C ages). I developed a method to link patterns of reoccupation with sea-level proxies by iterating relative sea level curves for a range of uplift rates. I find the best fit between relative sea-level and the stratigraphic patterns for an uplift rate of 1.5 +- 0.3 m/ka.
A Graphical User Interface named TerraceM® was developed in Matlab®. This novel software tool determines shoreline angles in wave-cut terraces under different geomorphic scenarios. To validate the methods, I select test sites in areas of available high-resolution LiDAR topography along the Maule earthquake rupture zone and in California, USA. The software allows determining the 3D location of the shoreline angle, which is a proxy for the estimation of permanent deformation rates. The method is based on linear interpolations to define the paleo platform and cliff on swath profiles. The shoreline angle is then located by intersecting these interpolations. The
accuracy and precision of TerraceM® was tested by comparing its results with previous assessments, and through an experiment with students in a computer lab setting at the University
of Potsdam.
I combined the methods developed to analyze wave-built and wave-cut terraces to assess regional patterns of permanent deformation along the (2010) Maule earthquake rupture. Wave-built terraces are tied using 12 Infra Red Stimulated luminescence ages (IRSL ages) and shoreline angles in wave-cut terraces are estimated from 170 aligned swath profiles. The comparison of coseismic slip, interseismic coupling, and permanent deformation, leads to three areas of high permanent uplift, terrace warping, and sharp fault offsets. These three areas correlate with regions of high slip and low coupling, as well as with the spatial limit of at least eight historical megathrust ruptures (M8-9.5). I propose that the zones of upwarping at Arauco and Topocalma reflect changes in frictional properties of the megathrust, which result in discrete boundaries for the propagation of mega earthquakes.
To explore the application of geomorphic markers and quantitative morphology in offshore areas I performed a local study of patterns of permanent deformation inferred from hitherto unrecognized drowned shorelines at the Arauco Bay, at the southern part of the (2010) Maule earthquake rupture zone. A multidisciplinary approach, including morphometry, sedimentology, paleontology, 3D morphoscopy, and a landscape Evolution Model is used to recognize, map, and assess local rates and patterns of permanent deformation in submarine environments. Permanent deformation patterns are then reproduced using elastic models to assess deformation rates of an active submarine splay fault defined as Santa Maria Fault System. The best fit suggests a reverse structure with a slip rate of 3.7 m/ka for the last 30 ka. The register of land level changes during the earthquake cycle at Santa Maria Island suggest that most of the deformation may be accrued through splay fault reactivation during mega earthquakes, like the (2010) Maule event. Considering a recurrence time of 150 to 200 years, as determined from historical and geological observations, slip between 0.3 and 0.7 m per event would be required to account for the 3.7 m/ka millennial slip rate. However, if the SMFS slips only every ~1000 years, representing a few megathrust earthquakes, then a slip of ~3.5 m per event would be required to account for the long- term rate. Such event would be equivalent to a magnitude ~6.7 earthquake capable to generate a local tsunami.
The results of this thesis provide novel and fundamental information regarding the amount of permanent deformation accrued in the crust, and the mechanisms responsible for this accumulation at millennial time-scales along the M8.8 Maule earthquake (2010) rupture zone. Furthermore, the results of this thesis highlight the application of quantitative geomorphology and the use of repeatable methods to determine permanent deformation, improve the accuracy of marine terrace assessments, and estimates of vertical deformation rates in tectonically active coastal areas. This is vital information for adequate coastal-hazard assessments and to anticipate realistic earthquake and tsunami scenarios.
In 1915, Alfred Wegener published his hypotheses of plate tectonics that revolutionised the world for geologists. Since then, many scientists have studied the evolution of continents and especially the geologic structure of orogens: the most visible consequence of tectonic processes. Although the morphology and landscape evolution of mountain belts can be observed due to surface processes, the driving force and dynamics at lithosphere scale are less well understood despite the fact that rocks from deeper levels of orogenic belts are in places exposed at the surface. In this thesis, such formerly deeply-buried (ultra-) high-pressure rocks, in particular eclogite facies series, have been studied in order to reveal details about the formation and exhumation conditions and rates and thus provide insights into the geodynamics of the most spectacular orogenic belt in the world: the Himalaya. The specific area investigated was the Kaghan Valley in Pakistan (NW Himalaya). Following closure of the Tethyan Ocean by ca. 55-50 Ma, the northward subduction of the leading edge of India beneath the Eurasian Plate and subsequent collision initiated a long-lived process of intracrustal thrusting that continues today. The continental crust of India – granitic basement, Paleozoic and Mesozoic cover series and Permo-Triassic dykes, sills and lavas – has been buried partly to mantle depths. Today, these rocks crop out as eclogites, amphibolites and gneisses within the Higher Himalayan Crystalline between low-grade metamorphosed rocks (600-640°C/ ca. 5 kbar) of the Lesser Himalaya and Tethyan sediments. Beside tectonically driven exhumation mechanisms the channel flow model, that describes a denudation focused ductile extrusion of low viscosity material developed in the middle to lower crust beneath the Tibetan Plateau, has been postulated. To get insights into the lithospheric and crustal processes that have initiated and driven the exhumation of this (ultra-) high-pressure rocks, mineralogical, petrological and isotope-geochemical investigations have been performed. They provide insights into 1) the depths and temperatures to which these rocks were buried, 2) the pressures and temperatures the rocks have experienced during their exhumation, 3) the timing of these processes 4) and the velocity with which these rocks have been brought back to the surface. In detail, through microscopical studies, the identification of key minerals, microprobe analyses, standard geothermobarometry and modelling using an effective bulk rock composition it has been shown that published exhumation paths are incomplete. In particular, the eclogites of the northern Kaghan Valley were buried to depths of 140-100 km (36-30 kbar) at 790-640°C. Subsequently, cooling during decompression (exhumation) towards 40-35 km (17-10 kbar) and 630-580°C has been superseded by a phase of reheating to about 720-650°C at roughly the same depth before final exhumation has taken place. In the southern-most part of the study area, amphibolite facies assemblages with formation conditions similar to the deduced reheating phase indicate a juxtaposition of both areas after the eclogite facies stage and thus a stacking of Indian Plate units. Radiometric dating of zircon, titanite and rutile by U-Pb and amphibole and micas by Ar-Ar reveal peak pressure conditions at 47-48 Ma. With a maximum exhumation rate of 14 cm/a these rocks reached the crust-mantle boundary at 40-35 km within 1 Ma. Subsequent exhumation (46-41 Ma, 40-35 km) decelerated to ca. 1 mm/a at the base of the continental crust but rose again to about 2 mm/a in the period of 41-31 Ma, equivalent to 35-20 km. Apatite fission track (AFT) and (U-Th)/He ages from eclogites, amphibolites, micaschists and gneisses yielded moderate Oligocene to Miocene cooling rates of about 10°C/Ma in the high altitude northern parts of the Kaghan Valley using the mineral-pair method. AFT ages are of 24.5±3.8 to 15.6±2.1 Ma whereas apatite (U-Th)/He analyses yielded ages between 21.0±0.6 and 5.3±0.2 Ma. The southern-most part of the Valley is dominated by younger late Miocene to Pliocene apatite fission track ages of 7.6±2.1 and 4.0±0.5 Ma that support earlier tectonically and petrologically findings of a juxtaposition and stack of Indian Plate units. As this nappe is tectonically lowermost, a later distinct exhumation and uplift driven by thrusting along the Main Boundary Thrust is inferred. A multi-stage exhumation path is evident from petrological, isotope-geochemical and low temperature thermochronology investigations. Buoyancy driven exhumation caused an initial rapid exhumation: exhumation as fast as recent normal plate movements (ca. 10 cm/a). As the exhuming units reached the crust-mantle boundary the process slowed down due to changes in buoyancy. Most likely, this exhumation pause has initiated the reheating event that is petrologically evident (e.g. glaucophane rimmed by hornblende, ilmenite overgrowth of rutile). Late stage processes involved widespread thrusting and folding with accompanied regional greenschist facies metamorphism, whereby contemporaneous thrusting on the Batal Thrust (seen by some authors equivalent to the MCT) and back sliding of the Kohistan Arc along the inverse reactivated Main Mantle Thrust caused final exposure of these rocks. Similar circumstances have been seen at Tso Morari, Ladakh, India, 200 km further east where comparable rock assemblages occur. In conclusion, as exhumation was already done well before the initiation of the monsoonal system, climate dependent effects (erosion) appear negligible in comparison to far-field tectonic effects.
Metabolically active microbial communities are present in a wide range of subsurface environments. Techniques like enumeration of microbial cells, activity measurements with radiotracer assays and the analysis of porewater constituents are currently being used to explore the subsurface biosphere, alongside with molecular biological analyses. However, many of these techniques reach their detection limits due to low microbial activity and abundance. Direct measurements of microbial turnover not just face issues of insufficient sensitivity, they only provide information about a single specific process but in sediments many different process can occur simultaneously. Therefore, the development of a new technique to measure total microbial activity would be a major improvement. A new tritium-based hydrogenase-enzyme assay appeared to be a promising tool to quantify total living biomass, even in low activity subsurface environments. In this PhD project total microbial biomass and microbial activity was quantified in different subsurface sediments using established techniques (cell enumeration and pore water geochemistry) as well as a new tritium-based hydrogenase enzyme assay. By using a large database of our own cell enumeration data from equatorial Pacific and north Pacific sediments and published data it was shown that the global geographic distribution of subseafloor sedimentary microbes varies between sites by 5 to 6 orders of magnitude and correlates with the sedimentation rate and distance from land. Based on these correlations, global subseafloor biomass was estimated to be 4.1 petagram-C and ~0.6 % of Earth's total living biomass, which is significantly lower than previous estimates. Despite the massive reduction in biomass the subseafloor biosphere is still an important player in global biogeochemical cycles. To understand the relationship between microbial activity, abundance and organic matter flux into the sediment an expedition to the equatorial Pacific upwelling area and the north Pacific Gyre was carried out. Oxygen respiration rates in subseafloor sediments from the north Pacific Gyre, which are deposited at sedimentation rates of 1 mm per 1000 years, showed that microbial communities could survive for millions of years without fresh supply of organic carbon. Contrary to the north Pacific Gyre oxygen was completely depleted within the upper few millimeters to centimeters in sediments of the equatorial upwelling region due to a higher supply of organic matter and higher metabolic activity. So occurrence and variability of electron acceptors over depth and sites make the subsurface a complex environment for the quantification of total microbial activity. Recent studies showed that electron acceptor processes, which were previously thought to thermodynamically exclude each other can occur simultaneously. So in many cases a simple measure of the total microbial activity would be a better and more robust solution than assays for several specific processes, for example sulfate reduction rates or methanogenesis. Enzyme or molecular assays provide a more general approach as they target key metabolic compounds. Since hydrogenase enzymes are ubiquitous in microbes, the recently developed tritium-based hydrogenase radiotracer assay is applied to quantify hydrogenase enzyme activity as a parameter of total living cell activity. Hydrogenase enzyme activity was measured in sediments from different locations (Lake Van, Barents Sea, Equatorial Pacific and Gulf of Mexico). In sediment samples that contained nitrate, we found the lowest cell specific enzyme activity around 10^(-5) nmol H_(2) cell^(-1) d^(-1). With decreasing energy yield of the electron acceptor used, cell-specific hydrogenase activity increased and maximum values of up to 1 nmol H_(2) cell^(-1) d^(-1) were found in samples with methane concentrations of >10 ppm. Although hydrogenase activity cannot be converted directly into a turnover rate of a specific process, cell-specific activity factors can be used to identify specific metabolism and to quantify the metabolically active microbial population. In another study on sediments from the Nankai Trough microbial abundance and hydrogenase activity data show that both the habitat and the activity of subseafloor sedimentary microbial communities have been impacted by seismic activities. An increase in hydrogenase activity near the fault zone revealed that the microbial community was supplied with hydrogen as an energy source and that the microbes were specialized to hydrogen metabolism.
In many procedures of seismic risk mitigation, ground motion simulations are needed to test systems or improve their effectiveness. For example they may be used to estimate the level of ground shaking caused by future earthquakes. Good physical models for ground motion simulation are also thought to be important for hazard assessment, as they could close gaps in the existing datasets. Since the observed ground motion in nature shows a certain variability, part of which cannot be explained by macroscopic parameters such as magnitude or position of an earthquake, it would be desirable that a good physical model is not only able to produce one single seismogram, but also to reveal this natural variability.
In this thesis, I develop a method to model realistic ground motions in a way that is computationally simple to handle, permitting multiple scenario simulations. I focus on two aspects of ground motion modelling. First, I use deterministic wave propagation for the whole frequency range – from static deformation to approximately 10 Hz – but account for source variability by implementing self-similar slip distributions and rough fault interfaces. Second, I scale the source spectrum so that the modelled waveforms represent the correct radiated seismic energy. With this scaling I verify whether the energy magnitude is suitable as an explanatory variable, which characterises the amount of energy radiated at high frequencies – the advantage of the energy magnitude being that it can be deduced from observations, even in real-time.
Applications of the developed method for the 2008 Wenchuan (China) earthquake, the 2003 Tokachi-Oki (Japan) earthquake and the 1994 Northridge (California, USA) earthquake show that the fine source discretisations combined with the small scale source variability ensure that high frequencies are satisfactorily introduced, justifying the deterministic wave propagation approach even at high frequencies. I demonstrate that the energy magnitude can be used to calibrate the high-frequency content in ground motion simulations.
Because deterministic wave propagation is applied to the whole frequency range, the simulation method permits the quantification of the variability in ground motion due to parametric uncertainties in the source description. A large number of scenario simulations for an M=6 earthquake show that the roughness of the source as well as the distribution of fault dislocations have a minor effect on the simulated variability by diminishing directivity effects, while hypocenter location and rupture velocity more strongly influence the variability. The uncertainty in energy magnitude, however, leads to the largest differences of ground motion amplitude between different events, resulting in a variability which is larger than the one observed.
For the presented approach, this dissertation shows (i) the verification of the computational correctness of the code, (ii) the ability to reproduce observed ground motions and (iii) the validation of the simulated ground motion variability. Those three steps are essential to evaluate the suitability of the method for means of seismic risk mitigation.
One of the most difficult issues when dealing with optical water remote-sensing is its acceptance as a useful application for environmental research. This problem is, on the one hand, concerned with the optical complexity and variability of the investigated natural media, and therefore the question arises as to the plausibility of the parameters derived from remote-sensing techniques. Detailed knowledge about the regional bio- and chemico-optical properties is required for such studies, however such information is seldom available for the sites of interest. On the other hand, the primary advantage of remote-sensing information, which is the provision of a spatial overview, may not be exploited fully by the disciplines that would benefit most from such information. It is often seen in a variety of disciplines that scientists have been primarily trained to look at discrete data sets, and therefore have no experience of incorporating information dealing with spatial heterogeneity. In this thesis, the opportunity was made available to assess the potential of Ocean Colour data to provide spatial and seasonal information about the surface waters of Lake Baikal (Siberia). While discrete limnological field data is available, the spatial extension of Lake Baikal is enormous (ca. 600 km), while the field data are limited to selected sites and expedition time windows. Therefore, this remote-sensing investigation aimed to support a multi-disciplinary limnological investigation within the framework of the paleoclimate EU-project ‘High Resolution CONTINENTal Paleoclimate Record in Lake Baikal, Siberia (CONTINENT)’ using spatial and seasonal information from the SeaWiFS satellite (NASA). From this, the SeaWiFS study evolved to become the first efficient bio-optical satellite study of Lake Baikal. During the course of three years, field work including spectral field measurements and water sampling, was carried out at Lake Baikal in Southern Siberia, and at the Mecklenburg and Brandenburg lake districts in Germany. The first step in processing the SeaWiFS satellite data involved adapting the SeaDAS (NASA) atmospheric-correction processing to match as close as possible the specific conditions of Lake Baikal. Next, various Chl-a algorithms were tested on the atmospherically-corrected optimized SeaWiFS data set (years 2001 to 2002), comparing the CONTINENT pigment ground-truth data with the Chl-a concentrations derived from the satellite data. This showed the high performance of the global Chl-a products OC2 and OC4 for the oligotrophic, transparent waters (bio-optical Case 1) of Lake Baikal. However, considerable Chl-a overestimation prevailed in bio-optical Case 2 areas for the case of discharge events. High-organic terrigenous input into Lake Baikal could be traced and information extracted using the SeaWiFS spectral data. Suspended Particulate Matter (SPM) was quantified by the regression of the SeaDAS attenuation coefficient as the optical parameter with SPM field data. Finally, the Chl-a and terrigenous input maps derived from the remote sensing data were used to assist with analyzing the relationships between the various discrete data obtained during the CONTINENT field work. Hence, plausible spatial and seasonal information describing autochthonous and allochthonous material in Lake Baikal could be provided by satellite data.Lake Baikal, with its bio-optical complexity and its different areas of Case 1 and Case 2 waters, is a very interesting case study for Ocean Colour analyses. Proposals for future Ocean Colour studies of Lake Baikal are discussed, including which bio-optical parameters for analytical models still need to be clarified by field investigations.
Throughout the last ~3 million years, the Earth's climate system was characterised by cycles of glacial and interglacial periods. The current warm period, the Holocene, is comparably stable and stands out from this long-term cyclicality. However, since the industrial revolution, the climate has been increasingly affected by a human-induced increase in greenhouse gas concentrations. While instrumental observations are used to describe changes over the past ~200 years, indirect observations via proxy data are the main source of information beyond this instrumental era. These data are indicators of past climatic conditions, stored in palaeoclimate archives around the Earth. The proxy signal is affected by processes independent of the prevailing climatic conditions. In particular, for sedimentary archives such as marine sediments and polar ice sheets, material may be redistributed during or after the initial deposition and subsequent formation of the archive. This leads to noise in the records challenging reliable reconstructions on local or short time scales. This dissertation characterises the initial deposition of the climatic signal and quantifies the resulting archive-internal heterogeneity and its influence on the observed proxy signal to improve the representativity and interpretation of climate reconstructions from marine sediments and ice cores.
To this end, the horizontal and vertical variation in radiocarbon content of a box-core from the South China Sea is investigated. The three-dimensional resolution is used to quantify the true uncertainty in radiocarbon age estimates from planktonic foraminifera with an extensive sampling scheme, including different sample volumes and replicated measurements of batches of small and large numbers of specimen. An assessment on the variability stemming from sediment mixing by benthic organisms reveals strong internal heterogeneity. Hence, sediment mixing leads to substantial time uncertainty of proxy-based reconstructions with error terms two to five times larger than previously assumed.
A second three-dimensional analysis of the upper snowpack provides insights into the heterogeneous signal deposition and imprint in snow and firn. A new study design which combines a structure-from-motion photogrammetry approach with two-dimensional isotopic data is performed at a study site in the accumulation zone of the Greenland Ice Sheet. The photogrammetry method reveals an intermittent character of snowfall, a layer-wise snow deposition with substantial contributions by wind-driven erosion and redistribution to the final spatially variable accumulation and illustrated the evolution of stratigraphic noise at the surface. The isotopic data show the preservation of stratigraphic noise within the upper firn column, leading to a spatially variable climate signal imprint and heterogeneous layer thicknesses. Additional post-depositional modifications due to snow-air exchange are also investigated, but without a conclusive quantification of the contribution to the final isotopic signature.
Finally, this characterisation and quantification of the complex signal formation in marine sediments and polar ice contributes to a better understanding of the signal content in proxy data which is needed to assess the natural climate variability during the Holocene.
The Central Pontides is an accretionary-type orogenic area within the Alpine-Himalayan orogenic belt characterized by pre-collisional tectonic continental growth. The region comprises Mesozoic subduction-accretionary complexes and an accreted intra-oceanic arc that are sandwiched between the Laurasian active continental margin and Gondwana-derived the Kırşehir Block. The subduction-accretion complexes mainly consist of an Albian-Turonian accretionary wedge representing the Laurasian active continental margin. To the north, the wedge consists of slate/phyllite and metasandstone intercalation with recrystallized limestone, Na-amphibole-bearing metabasite (PT= 7–12 kbar and 400 ± 70 ºC) and tectonic slices of serpentinite representing accreted distal part of a large Lower Cretaceous submarine turbidite fan deposited on the Laurasian active continental margin that was subsequently accreted and metamorphosed. Raman spectra of carbonaceous material (RSCM) of the metapelitic rocks revealed that the metaflysch sequence consists of metamorphic packets with distinct peak metamorphic temperatures. The majority of the metapelites are low-temperature (ca. 330 °C) slates characterized by lack of differentiation of the graphite (G) and D2 defect bands. They possibly represent offscraped distal turbidites along the toe of the Albian accretionary wedge. The rest are phyllites that are characterized by slightly pronounced G band with D2 defect band occurring on its shoulder. Peak metamorphic temperatures of these phyllites are constrained to 370-385 °C. The phyllites are associated with a strip of incipient blueschist facies metabasites which are found as slivers within the offscraped distal turbidites. They possibly represent underplated continental metasediments together with oceanic crustal basalt along the basal décollement. Tectonic emplacement of the underplated rocks into the offscraped distal turbidites was possibly achieved by out-of-sequence thrusting causing tectonic thickening and uplift of the wedge. 40Ar/39Ar phengite ages from the phyllites are ca. 100 Ma, indicating Albian subduction and regional HP metamorphism.
The accreted continental metasediments are underlain by HP/LT metamorphic rocks of oceanic origin along an extensional shear zone. The oceanic metamorphic sequence mainly comprises tectonically thickened deep-seated eclogite to blueschist facies metabasites and micaschists. In the studied area, metabasites are epidote-blueschists locally with garnet (PT= 17 ± 1 kbar and 500 ± 40 °C). Lawsonite-blueschists are exposed as blocks along the extensional shear zone (PT= 14 ± 2 kbar and 370–440 °C). They are possibly associated with low shear stress regime of the initial stage of convergence. Close to the shear zone, the footwall micaschists consist of quartz, phengite, paragonite, chlorite, rutile with syn-kinematic albite porphyroblast formed by pervasive shearing during exhumation. These types of micaschists are tourmaline-bearing and their retrograde nature suggests high-fluid flux along shear zones. Peak metamorphic mineral assemblages are partly preserved in the chloritoid-micaschist farther away from the shear zone representing the zero strain domains during exhumation. Three peak metamorphic assemblages are identified and their PT conditions are constrained by pseudosections produced by Theriak-Domino and by Raman spectra of carbonaceous material: 1) garnet-chloritoid-glaucophane with lawsonite pseudomorphs (P= 17.5 ± 1 kbar, T: 390-450 °C) 2) chloritoid with glaucophane pseudomorphs (P= 16-18 kbar, T: 475 ± 40 °C) and 3) relatively high-Mg chloritoid (17%) with jadeite pseudomorphs (P= 22-25 kbar; T: 440 ± 30 °C) in addition to phengite, paragonite, quartz, chlorite, rutile and apatite. The last mineral assemblage is interpreted as transformation of the chloritoid + glaucophane assemblage to chloritoid + jadeite paragenesis with increasing pressure. Absence of tourmaline suggests that the chloritoid-micaschist did not interact with B-rich fluids during zero strain exhumation. 40Ar/39Ar phengite age of a pervasively sheared footwall micaschist is constrained to 100.6 ± 1.3 Ma and that of a chloritoid-micaschist is constrained to 91.8 ± 1.8 Ma suggesting exhumation during on-going subduction with a southward younging of the basal accretion and the regional metamorphism. To the south, accretionary wedge consists of blueschist and greenschist facies metabasite, marble and volcanogenic metasediment intercalation. 40Ar/39Ar phengite dating reveals that this part of the wedge is of Middle Jurassic age partly overprinted during the Albian. Emplacement of the Middle Jurassic subduction-accretion complexes is possibly associated with obliquity of the Albian convergence.
Peak metamorphic assemblages and PT estimates of the deep-seated oceanic metamorphic sequence suggest tectonic stacking within wedge with different depths of burial. Coupling and exhumation of the distinct metamorphic slices are controlled by decompression of the wedge possibly along a retreating slab. Structurally, decompression of the wedge is evident by an extensional shear zone and the footwall micaschists with syn-kinematic albite porphyroblasts. Post-kinematic garnets with increasing grossular content and pseudomorphing minerals within the chloritoid-micaschists also support decompression model without an extra heating.
Thickening of subduction-accretionary complexes is attributed to i) significant amount of clastic sediment supply from the overriding continental domain and ii) deep level basal underplating by propagation of the décollement along a retreating slab. Underplating by basal décollement propagation and subsequent exhumation of the deep-seated subduction-accretion complexes are connected and controlled by slab rollback creating a necessary space for progressive basal accretion along the plate interface and extension of the wedge above for exhumation of the tectonically thickened metamorphic sequences. This might be the most common mechanism of the tectonic thickening and subsequent exhumation of deep-seated HP/LT subduction-accretion complexes.
To the south, the Albian-Turonian accretionary wedge structurally overlies a low-grade volcanic arc sequence consisting of low-grade metavolcanic rocks and overlying metasedimentary succession is exposed north of the İzmir-Ankara-Erzincan suture (İAES), separating Laurasia from Gondwana-derived terranes. The metavolcanic rocks mainly consist of basaltic andesite/andesite and mafic cognate xenolith-bearing rhyolite with their pyroclastic equivalents, which are interbedded with recrystallized pelagic limestone and chert. The metavolcanic rocks are stratigraphically overlain by recrystallized micritic limestone with rare volcanogenic metaclastic rocks. Two groups can be identified based on trace and rare earth element characteristics. The first group consists of basaltic andesite/andesite (BA1) and rhyolite with abundant cognate gabbroic xenoliths. It is characterized by relative enrichment of LREE with respect to HREE. The rocks are enriched in fluid mobile LILE, and strongly depleted in Ti and P reflecting fractionation of Fe-Ti oxides and apatite, which are found in the mafic cognate xenoliths. Abundant cognate gabbroic xenoliths and identical trace and rare earth elements compositions suggest that rhyolites and basaltic andesites/andesites (BA1) are cogenetic and felsic rocks were derived from a common mafic parental magma by fractional crystallization and accumulation processes. The second group consists only of basaltic andesites (BA2) with flat REE pattern resembling island arc tholeiites. Although enriched in LILE, this group is not depleted in Ti or P.
Geochemistry of the metavolcanic rocks indicates supra-subduction volcanism evidenced by depletion of HFSE and enrichment of LILE. The arc sequence is sandwiched between an Albian-Turonian subduction-accretionary complex representing the Laurasian active margin and an ophiolitic mélange. Absence of continent derived detritus in the arc sequence and its tectonic setting in a wide Cretaceous accretionary complex suggest that the Kösdağ Arc was intra-oceanic. This is in accordance with basaltic andesites (BA2) with island arc tholeiite REE pattern.
Zircons from two metarhyolite samples give Late Cretaceous (93.8 ± 1.9 and 94.4 ± 1.9 Ma) U/Pb ages. Low-grade regional metamorphism of the intra-oceanic arc sequence is constrained 69.9 ± 0.4 Ma by 40Ar/39Ar dating on metamorphic muscovite from a metarhyolite indicating that the arc sequence became part of a wide Tethyan Cretaceous accretionary complex by the latest Cretaceous. The youngest 40Ar/39Ar phengite age from the overlying subduction-accretion complexes is 92 Ma confirming southward younging of an accretionary-type orogenic belt. Hence, the arc sequence represents an intra-oceanic paleo-arc that formed above the sinking Tethyan slab and finally accreted to Laurasian active continental margin. Abrupt non-collisional termination of arc volcanism was possibly associated with southward migration of the arc volcanism similar to the Izu-Bonin-Mariana arc system.
The intra-oceanic Kösdağ Arc is coeval with the obducted supra-subduction ophiolites in NW Turkey suggesting that it represents part of the presumed but missing incipient intra-oceanic arc associated with the generation of the regional supra-subduction ophiolites. Remnants of a Late Cretaceous intra-oceanic paleo-arc and supra-subduction ophiolites can be traced eastward within the Alp-Himalayan orogenic belt. This reveals that Late Cretaceous intra-oceanic subduction occurred as connected event above the sinking Tethyan slab. It resulted as arc accretion to Laurasian active margin and supra-subduction ophiolite obduction on Gondwana-derived terranes.
Salt pans also termed playas are common landscape features of hydrologically closed basins in arid and semiarid zones, where evaporation significantly exceeds the local precipitation. The analysis and monitoring of salt pan environments is important for the evaluation of current and future impact of these landscape features. Locally, salt pans have importance for the ecosystem, wildlife and human health, and through dust emissions they influence the climate on regional and global scales. Increasing economic exploitation of these environments in the last years, e.g. by brine extraction for raw materials, as well as climate change severely affect the water, material and energy balance of these systems. Optical remote sensing has the potential to characterise salt pan environments and to increase the understanding of processes in playa basins, as well as to assess wider impacts and feedbacks that exist between climate forcing and human intervention in their regions. Remote sensing techniques can provide information for extensive regions on a high temporal basis compared to traditional field samples and ground observations. Specifically, for salt pans that are often challenging to study because of their large size, remote location, and limited accessibility due to missing infrastructure and ephemeral flooding. Furthermore, the availability of current and upcoming hyperspectral remote sensing data opened the opportunity for the analyses of the complex reflectance signatures that relate to the mineralogical mixtures found in the salt pan sediments. However, these new advances in sensor technology, as well as increased data availability currently have not been fully explored for the study of salt pan environments. The potential of new sensors needs to be assessed and state of the art methods need to be adapted and improved to provide reliable information for in depth analysis of processes and characterisation of the recent condition, as well as to support long-term monitoring and to evaluate environmental impacts of changing climate and anthropogenic activity.
This thesis provides an assessment of the capabilities of optical remote sensing for the study of salt pan environments that combines the information of hyperspectral data with the increased temporal coverage of multispectral observations for a more complete understanding of spatial and temporal complexity of salt pan environments using the Omongwa salt pan located in the south-west Kalahari as a test site. In particular, hyperspectral data are used for unmixing of the mineralogical surface composition, spectral feature-based modelling for quantification of main crust components, as well as time-series based classification of multispectral data for the assessment of the long-term dynamic and the analysis of the seasonal process regime. The results show that the surface of the Omongwa pan can be categorized into three major crust types based on diagnostic absorption features and mineralogical ground truth data. The mineralogical crust types can be related to different zones of surface dynamic as well as pan morphology that influences brine flow during the pan inundation and desiccation cycles. Using current hyperspectral imagery, as well as simulated data of upcoming sensors, robust quantification of the gypsum component could be derived. For the test site the results further indicate that the crust dynamic is mainly driven by flooding events in the wet season, but it is also influenced by temperature and aeolian activity in the dry season. Overall, the scientific outcomes show that optical remote sensing can provide a wide range of information helpful for the study of salt pan environments. The thesis also highlights that remote sensing approaches are most relevant, when they are adapted to the specific site conditions and research scenario and that upcoming sensors will increase the potential for mineralogical, sedimentological and geomorphological analysis, and will improve the monitoring capabilities with increased data availability.
Geochemical processes such as mineral dissolution and precipitation alter the microstructure of rocks, and thereby affect their hydraulic and mechanical behaviour. Quantifying these property changes and considering them in reservoir simulations is essential for a sustainable utilisation of the geological subsurface. Due to the lack of alternatives, analytical methods and empirical relations are currently applied to estimate evolving hydraulic and mechanical rock properties associated with chemical reactions. However, the predictive capabilities of analytical approaches remain limited, since they assume idealised microstructures, and thus are not able to reflect property evolution for dynamic processes. Hence, aim of the present thesis is to improve the prediction of permeability and stiffness changes resulting from pore space alterations of reservoir sandstones.
A detailed representation of rock microstructure, including the morphology and connectivity of pores, is essential to accurately determine physical rock properties. For that purpose, three-dimensional pore-scale models of typical reservoir sandstones, obtained from highly resolved micro-computed tomography (micro-CT), are used to numerically calculate permeability and stiffness. In order to adequately depict characteristic distributions of secondary minerals, the virtual samples are systematically altered and resulting trends among the geometric, hydraulic, and mechanical rock properties are quantified. It is demonstrated that the geochemical reaction regime controls the location of mineral precipitation within the pore space, and thereby crucially affects the permeability evolution. This emphasises the requirement of determining distinctive porosity-permeability relationships
by means of digital pore-scale models. By contrast, a substantial impact of spatial alterations patterns on the stiffness evolution of reservoir sandstones are only observed in case of certain microstructures, such as highly porous granular rocks or sandstones comprising framework-supporting cementations. In order to construct synthetic granular samples a process-based approach is proposed including grain deposition and diagenetic cementation. It is demonstrated that the generated samples reliably represent the microstructural complexity of natural sandstones. Thereby, general limitations of imaging techniques can be overcome and various realisations of granular rocks can be flexibly produced. These can be further altered by virtual experiments, offering a fast and cost-effective way to examine the impact of precipitation, dissolution or fracturing on various petrophysical correlations.
The presented research work provides methodological principles to quantify trends in permeability and stiffness resulting from geochemical processes. The calculated physical property relations are directly linked to pore-scale alterations, and thus have a higher accuracy than commonly applied analytical approaches. This will considerably improve the predictive capabilities of reservoir models, and is further relevant to assess and reduce potential risks, such as productivity or injectivity losses as well as reservoir compaction or fault reactivation. Hence, the proposed method is of paramount importance for a wide range of natural and engineered subsurface applications, including geothermal energy systems, hydrocarbon reservoirs, CO2 and energy storage as well as hydrothermal deposit exploration.
Landscapes evolve in a complex interplay between climate and tectonics. Thus, the geomorphic characteristics of a landscape can only be understood if both, climatic and tectonic signals of past and ongoing processes can be identified. In order to evaluate the impact of both forcing factors it is crucial to quantify the evolution of geomorphic markers in natural environments. The Cenozoic Andes are an ideal setting to evaluate tectonic and climatic aspects of landscape evolution at different time and length scales in different natural compartments. The Andean Cordillera constitutes the type subduction orogen and is associated with the subduction of the oceanic Nazca Plate beneath the South American continent since at least 200 million years. In Chile and the adjacent regions this convergent margin is characterized by active tectonics, volcanism, and mountain building. Importantly, along the coast of Chile megathrust earthquakes occur frequently and influence landscape evolution. In fact, the largest earthquake ever recorded occurred in south-central Chile in 1960 and comprised a rupture zone of ~ 1000 km length. However, on longer time scales beyond historic documentation of seismicity it is not well known, how such seismotectonic segments have behaved and how they influence the geomorphic evolution of the coastal realms. With several semi-independent morphotectonic segments, recurrent megathrust earthquakes, and a plethora of geomorphic features indicating sustained tectonism, the margin of Chile is thus a key area to study relationships between surface processes and tectonics. In this study, I combined geomorphology, geochronology, sedimentology, and morphometry to quantify the Pliocene-Pleistocene landscape evolution of the tectonically active south-central Chile forearc. Thereby, I provide (1) new results about the influence of seismotectonic forearc segmentation on the geomorphic evolution and (2) new insights in the interaction between climate and tectonics with respect to the morphology of the Chilean forearc region. In particular, I show that the forearc is characterized by three long-term segments that are not correlated with short-lived earthquake-rupture zones that may. These segments are the Nahuelbuta, Toltén, and Bueno segments, each recording a distinct geomorphic and tectonic evolution. The Nahuelbuta and Bueno segments are undergoing active tectonic uplift. The long-term behavior of these two segments is manifested in form of two doubly plunging, growing antiforms that constitute an integral part of the Coastal Cordillera and record the uplift of marine and river terraces. In addition, these uplifting areas have caused major changes in flow directions or rivers. In contrast, the Toltén segment, situated between the two other segments, appears to be quasi-stable. In order to further quantify uplift and incision in the actively deforming Nahuelbuta segment, I dated an erosion surface and fluvial terraces in the Coastal Cordillera with cosmogenic 10Be and 26Al and optically stimulated luminescence, respectively. According to my results, late Pleistocene uplift rates corresponding to 0.88 mm a-1 are faster than surface-uplift rates averaging over the last 5 Ma, which are in the range of 0.21 mm a-1. This discrepancy suggests that surface uplift is highly variable in time and space and might preferably concentrate along reverse faults as indicated by a late Pleistocene flow reversal. In addition, the results of exposure dating with cosmogenic 10Be and 26Al indicate that the morphotectonic segmentation of this region of the forearc has been established in Pliocene time, coeval with the initiation of uplift of the Coastal Cordillera about 5 Ma ago, inferred to be related to a shift in subduction mode from erosion to accretion. Finally, I dated volcanic clasts obtained from alluvial surfaces in the Central Depression, a low-relief sector separating the Coastal from the Main Cordillera, with stable cosmogenic 3He and 21Ne, in order to reveal the controls of sediment accumulation in the forearc. My results document that these gently sloping surfaces have been deposited 150 to 300 ka ago. This deposition may be related to changes in the erosional regime during glacial episodes. Taken together, the data indicates that the overall geomorphic expression of the forearc is of post-Miocene age and may be intimately related to a climatic overprint of the tectonic system. This climatic forcing is also reflected in the topography and local relief of the Central and Southern Andes that vary considerably along the margin, determined by the dominant surface process that in turn is eventually controlled by climate. However, relief also partly reflects surface processes that have taken place under past climatic conditions. This emphasizes that due care has to be exercised when interpreting landscapes as mirrors of modern climates.
Estuarine marshes are ecosystems that are situated at the transition zone between land and water and are thus controlled by physical and biological interactions. Marsh vegetation offers important ecosystem services by filtrating solid and dissolved substances from the water and providing habitat. By buffering a large part of the arriving flow velocity, attenuating wave energy and serving as erosion control for riverbanks, tidal marshes furthermore reduce the destructive effects of storm surges and storm waves and thus contribute to ecosystem-based shore protection. However, in many estuaries, extensive embankments, artificial bank protection, river dredging and agriculture threaten tidal marshes. Global warming might entail additional risks, such as changes in water levels, an increase of the tidal amplitude and a resulting shift of the salinity zones. This can affect the dynamics of the shore and foreland vegetation, and vegetation belts can be narrowed or fragmented. Against this background, it is crucial to gain a better understanding of the processes underlying the spatio temporal vegetation dynamics in brackish marshes. Furthermore, a better understanding of how plant-habitat relationships generate patterns in tidal marsh vegetation is vital to maintain ecosystem functions and assess the response of marshes to environmental change as well as the success of engineering and restoration projects.
For this purpose, three research objectives were addressed within this thesis: (1) to explore the possibility of vegetation serving as self-adaptive shore protection by quantifying the reduction of current velocity in the vegetation belt and the morphologic plasticity of a brackish marsh pioneer, (2) to disentangle the roles of abiotic factors and interspecific competition on species distribution and stand characteristics in brackish marshes, and (3) to develop a mechanistic vegetation model that helps analysing the influence of habitat conditions on the spatio-temporal dynamic of tidal marsh vegetation. These aspects were investigated using a combination of field studies and statistical as well as process-based modelling.
To explore the possibility of vegetation serving as self-adaptive coastal protection, in the first study, we measured current velocity with and without living vegetation, recorded ramet density and plant thickness during two growing periods at two locations in the Elbe estuary and assessed the adaptive value of a larger stem diameter of plants at locations with higher mechanical stress by biomechanical measurements. The results of this study show that under non-storm conditions, the vegetation belt of the marsh pioneer Bolboschoenus maritimus is able to buffer a large proportion of the flow velocity. We were furthermore able to show that morphological traits of plant species are adapted to hydrodynamic forces by demonstrating a positive correlation between ramet thickness and cross-shore current. In addition, our measurements revealed that thicker ramets growing at the front of the vegetation belt have a significantly higher stability than ramets inside the vegetation belt. This self-adaptive effect improves the ability of B. maritimus to grow and persist in the pioneer zone and could provide an adaptive value in habitats with high mechanical stress.
In the second study, we assessed the distribution of the two marsh species and a set of stand characteristics, namely aboveground and belowground biomass, ramet density, ramet height and the percentage of flowering ramets. Furthermore, we collected information on several abiotic habitat factors to test their effect on plant growth and zonation with generalised linear models (GLMs). Our results demonstrate that flow velocity is the main factor controlling the distribution of Bolboschoenus maritimus and Phragmites australis. Additionally, inundation height and duration, as well as intraspecific competition affect distribution patterns. This study furthermore shows that cross-shore flow velocity does not only directly influence the distribution of the two marsh species, but also alters the plants’ occurrence relative to inun-dation height and duration. This suggests an effect of cross-shore flow velocity on their tolerance to inundation. The analysis of the measured stand characteristics revealed a negative effect of total flow velocity on all measured parameters of B. maritimus and thus confirmed our expectation that flow velocity is a decisive stressor which influences the growth of this species.
To gain a better understanding of the processes and habitat factors influencing the spatio-temporal vegetation dynamics in brackish marshes, I built a spatially explicit, mechanistic model applying a pattern-oriented modelling approach. A sensitivity analysis of the para-meters of this dynamic habitat-macrophyte model HaMac suggests that rhizome growth is the key process for the lateral dynamics of brackish marshes. From the analysed habitat factors, P. australis patterns were mainly influenced by flow velocity. The competition with P. australis was of key importance for the belowground biomass of B. maritimus. Concerning vegetation dynamics, the model results emphasise that without the effect of flow velocity the B. maritimus vegetation belt would expand into the tidal flat at locations with present vegetation recession, suggesting that flow velocity is the main reason for vegetation recession at exposed locations.
Overall, the results of this thesis demonstrate that brackish marsh vegetation considerably contributes to flow reduction under average flow conditions and can hence be a valuable component of shore-protection schemes. At the same time, the distribution, growth and expansion of tidal marsh vegetation is substantially influenced by flow. Altogether, this thesis provides a clear step forward in understanding plant-habitat interactions in tidal marshes. Future research should integrate studies of vertical marsh accretion with research on the factors that control the lateral position of marshes.
The global carbon cycle is closely linked to Earth’s climate. In the context of continuously unchecked anthropogenic CO₂ emissions, the importance of natural CO₂ bond and carbon storage is increasing. An important biogenic mechanism of natural atmospheric CO₂ drawdown is the photosynthetic carbon fixation in plants and the subsequent longterm deposition of plant detritus in sediments.
The main objective of this thesis is to identify factors that control mobilization and transport of plant organic matter (pOM) through rivers towards sedimentation basins. I investigated this aspect in the eastern Nepalese Arun Valley. The trans-Himalayan Arun River is characterized by a strong elevation gradient (205 − 8848 m asl) that is accompanied by strong changes in ecology and climate ranging from wet tropical conditions in the Himalayan forelad to high alpine tundra on the Tibetan Plateau. Therefore, the Arun is an excellent natural laboratory, allowing the investigation of the effect of vegetation cover, climate, and topography on plant organic matter mobilization and export in tributaries along the gradient.
Based on hydrogen isotope measurements of plant waxes sampled along the Arun River and its tributaries, I first developed a model that allows for an indirect quantification of pOM contributed to the mainsetm by the Arun’s tributaries. In order to determine the role of climatic and topographic parameters of sampled tributary catchments, I looked for significant statistical relations between the amount of tributary pOM export and tributary characteristics (e.g. catchment size, plant cover, annual precipitation or runoff, topographic measures). On one hand, I demonstrated that pOMsourced from the Arun is not uniformly derived from its entire catchment area. On the other, I showed that dense vegetation is a necessary, but not sufficient, criterion for high tributary pOM export. Instead, I identified erosion and rainfall and runoff as key factors controlling pOM sourcing in the Arun Valley. This finding is supported by terrestrial cosmogenic nuclide concentrations measured on river sands along the Arun and its tributaries in order to quantify catchment wide denudation rates. Highest denudation rates corresponded well with maximum pOM mobilization and export also suggesting the link between erosion and pOM sourcing.
The second part of this thesis focusses on the applicability of stable isotope records such as plant wax n-alkanes in sediment archives as qualitative and quantitative proxy for the variability of past Indian Summer Monsoon (ISM) strength. First, I determined how ISM strength affects the hydrogen and oxygen stable isotopic composition (reported as δD and δ18O values vs. Vienna Standard Mean Ocean Water) of precipitation in the Arun Valley and if this amount effect (Dansgaard, 1964) is strong enough to be recorded in potential paleo-ISM isotope proxies. Second, I investigated if potential isotope records across the Arun catchment reflect ISM strength dependent precipitation δD values only, or if the ISM isotope signal is superimposed by winter precipitation or glacial melt. Furthermore, I tested if δD values of plant waxes in fluvial deposits reflect δD values of environmental waters in the respective catchments.
I showed that surface water δD values in the Arun Valley and precipitation δD from south of the Himalaya both changed similarly during two consecutive years (2011 & 2012) with distinct ISM rainfall amounts (~20% less in 2012). In order to evaluate the effect of other water sources (Winter-Westerly precipitation, glacial melt) and evapotranspiration in the Arun Valley, I analysed satellite remote sensing data of rainfall distribution (TRMM 3B42V7), snow cover (MODIS MOD10C1), glacial coverage (GLIMSdatabase, Global Land Ice Measurements from Space), and evapotranspiration (MODIS MOD16A2). In addition to the predominant ISM in the entire catchment I found through stable isotope analysis of surface waters indications for a considerable amount of glacial melt derived from high altitude tributaries and the Tibetan Plateau. Remotely sensed snow cover data revealed that the upper portion of the Arun also receives considerable winter precipitation, but the effect of snow melt on the Arun Valley hydrology could not be evaluated as it takes place in early summer, several months prior to our sampling campaigns. However, I infer that plant wax records and other potential stable isotope proxy archives below the snowline are well-suited for qualitative, and potentially quantitative, reconstructions of past changes of ISM strength.
Sinkholes and depressions are typical landforms of karst regions. They pose a considerable natural hazard to infrastructure, agriculture, economy and human life in affected areas worldwide. The physio-chemical processes of sinkholes and depression formation are manifold, ranging from dissolution and material erosion in the subsurface to mechanical subsidence/failure of the overburden. This thesis addresses the mechanisms leading to the development of sinkholes and depressions by using complementary methods: remote sensing, distinct element modelling and near-surface geophysics.
In the first part, detailed information about the (hydro)-geological background, ground structures, morphologies and spatio-temporal development of sinkholes and depressions at a very active karst area at the Dead Sea are derived from satellite image analysis, photogrammetry and geologic field surveys. There, clusters of an increasing number of sinkholes have been developing since the 1980s within large-scale depressions and are distributed over different kinds of surface materials: clayey mud, sandy-gravel alluvium and lacustrine evaporites (salt). The morphology of sinkholes differs depending in which material they form: Sinkholes in sandy-gravel alluvium and salt are generally deeper and narrower than sinkholes in the interbedded evaporite and mud deposits. From repeated aerial surveys, collapse precursory features like small-scale subsidence, individual holes and cracks are identified in all materials. The analysis sheds light on the ongoing hazardous subsidence process, which is driven by the base-level fall of the Dead Sea and by the dynamic formation of subsurface water channels.
In the second part of this thesis, a novel, 2D distinct element geomechanical modelling approach with the software PFC2D-V5 to simulating individual and multiple cavity growth and sinkhole and large-scale depression development is presented. The approach involves a stepwise material removal technique in void spaces of arbitrarily shaped geometries and is benchmarked by analytical and boundary element method solutions for circular cavities. Simulated compression and tension tests are used to calibrate model parameters with bulk rock properties for the materials of the field site. The simulations show that cavity and sinkhole evolution is controlled by material strength of both overburden and cavity host material, the depth and relative speed of the cavity growth and the developed stress pattern in the subsurface. Major findings are: (1) A progressively deepening differential subrosion with variable growth speed yields a more fragmented stress pattern with stress interaction between the cavities. It favours multiple sinkhole collapses and nesting within large-scale depressions. (2) Low-strength materials do not support large cavities in the material removal zone, and subsidence is mainly characterised by gradual sagging into the material removal zone with synclinal bending. (3) High-strength materials support large cavity formation, leading to sinkhole formation by sudden collapse of the overburden. (4) Large-scale depression formation happens either by coalescence of collapsing holes, block-wise brittle failure, or gradual sagging and lateral widening.
The distinct element based approach is compared to results from remote sensing and geophysics at the field site. The numerical simulation outcomes are generally in good agreement with derived morphometrics, documented surface and subsurface structures as well as seismic velocities. Complementary findings on the subrosion process are provided from electric and seismic measurements in the area.
Based on the novel combination of methods in this thesis, a generic model of karst landform evolution with focus on sinkhole and depression formation is developed. A deepening subrosion system related to preferential flow paths evolves and creates void spaces and subsurface conduits. This subsequently leads to hazardous subsidence, and the formation of sinkholes within large-scale depressions. Finally, a monitoring system for shallow natural hazard phenomena consisting of geodetic and geophysical observations is proposed for similarly affected areas.
With Arctic ground as a huge and temperature-sensitive carbon reservoir, maintaining low ground temperatures and frozen conditions to prevent further carbon emissions that contrib-ute to global climate warming is a key element in humankind’s fight to maintain habitable con-ditions on earth. Former studies showed that during the late Pleistocene, Arctic ground condi-tions were generally colder and more stable as the result of an ecosystem dominated by large herbivorous mammals and vast extents of graminoid vegetation – the mammoth steppe. Characterised by high plant productivity (grassland) and low ground insulation due to animal-caused compression and removal of snow, this ecosystem enabled deep permafrost aggrad-ation. Now, with tundra and shrub vegetation common in the terrestrial Arctic, these effects are not in place anymore. However, it appears to be possible to recreate this ecosystem local-ly by artificially increasing animal numbers, and hence keep Arctic ground cold to reduce or-ganic matter decomposition and carbon release into the atmosphere.
By measuring thaw depth, total organic carbon and total nitrogen content, stable carbon iso-tope ratio, radiocarbon age, n-alkane and alcohol characteristics and assessing dominant vegetation types along grazing intensity transects in two contrasting Arctic areas, it was found that recreating conditions locally, similar to the mammoth steppe, seems to be possible. For permafrost-affected soil, it was shown that intensive grazing in direct comparison to non-grazed areas reduces active layer depth and leads to higher TOC contents in the active layer soil. For soil only frozen on top in winter, an increase of TOC with grazing intensity could not be found, most likely because of confounding factors such as vertical water and carbon movement, which is not possible with an impermeable layer in permafrost. In both areas, high animal activity led to a vegetation transformation towards species-poor graminoid-dominated landscapes with less shrubs. Lipid biomarker analysis revealed that, even though the available organic material is different between the study areas, in both permafrost-affected and sea-sonally frozen soils the organic material in sites affected by high animal activity was less de-composed than under less intensive grazing pressure. In conclusion, high animal activity af-fects decomposition processes in Arctic soils and the ground thermal regime, visible from reduced active layer depth in permafrost areas. Therefore, grazing management might be utilised to locally stabilise permafrost and reduce Arctic carbon emissions in the future, but is likely not scalable to the entire permafrost region.
Interactions and feedbacks between tectonics, climate, and upper plate architecture control basin geometry, relief, and depositional systems. The Andes is part of a longlived continental margin characterized by multiple tectonic cycles which have strongly modified the Andean upper plate architecture. In the Andean retroarc, spatiotemporal variations in the structure of the upper plate and tectonic regimes have resulted in marked along-strike variations in basin geometry, stratigraphy, deformational style, and mountain belt morphology. These along-strike variations include high-elevation plateaus (Altiplano and Puna) associated with a thin-skin fold-and-thrust-belt and thick-skin deformation in broken foreland basins such as the Santa Barbara system and the Sierras Pampeanas. At the confluence of the Puna Plateau, the Santa Barbara system and the Sierras Pampeanas, major along-strike changes in upper plate architecture, mountain belt morphology, basement exhumation, and deformation style can be recognized. I have used a source to sink approach to unravel the spatiotemporal tectonic evolution of the Andean retroarc between 26 and 28°S. I obtained a large low-temperature thermochronology data set from basement units which includes apatite fission track, apatite U-Th-Sm/He, and zircon U-Th/He (ZHe) cooling ages. Stratigraphic descriptions of Miocene units were temporally constrained by U-Pb LA-ICP-MS zircon ages from interbedded pyroclastic material.
Modeled ZHe ages suggest that the basement of the study area was exhumed during the Famatinian orogeny (550-450 Ma), followed by a period of relative tectonic quiescence during the Paleozoic and the Triassic. The basement experienced horst exhumation during the Cretaceous development of the Salta rift. After initial exhumation, deposition of thick Cretaceous syn-rift strata caused reheating of several basement blocks within the Santa Barbara system. During the Eocene-Oligocene, the Andean compressional setting was responsible for the exhumation of several disconnected basement blocks. These exhumed blocks were separated by areas of low relief, in which humid climate and low erosion rates facilitated the development of etchplains on the crystalline basement. The exhumed basement blocks formed an Eocene to Oligocene broken foreland basin in the back-bulge depozone of the Andean foreland. During the Early Miocene, foreland basin strata filled up the preexisting Paleogene topography. The basement blocks in lower relief positions were reheated; associated geothermal gradients were higher than 25°C/km. Miocene volcanism was responsible for lateral variations on the amount of reheating along the Campo-Arenal basin. Around 12 Ma, a new deformational phase modified the drainage network and fragmented the lacustrine system. As deformation and rock uplift continued, the easily eroded sedimentary cover was efficiently removed and reworked by an ephemeral fluvial system, preventing the development of significant relief. After ~6 Ma, the low erodibility of the basement blocks which began to be exposed caused relief increase, leading to the development of stable fluvial systems. Progressive relief development modified atmospheric circulation, creating a rainfall gradient. After 3 Ma, orographic rainfall and high relief lead to the development of proximal fluvial-gravitational depositional systems in the surrounding basins.
En el presente trabajo se realizó una investigación multidisciplinaria combinando métodos de geomorfología tectónica con estudios geofisicos y estructurales, focalizados principalmente en la caracterización neotectónica de ambos faldeos de la sierra de La Candelaria y del extremo sur de la cuenca de Metán. La zona de estudio se encuentra ubicada en la región limítrofe entre las provincias de Salta y Tucumán y pertenece a la provincia geológica del Sistema Santa Bárbara.
El principal objetivo consistió en contextualizar las evidencias de actividad tectónica cuaternaria de la región mediante la propuesta de un modelo estructural novedoso, con el propósito de incrementar la información disponible sobre estructuras neotectónicas y su potencial sismogénico. Con este fin, se aplicaron e integraron diversas técnicas tales como la interpretación de líneas sísmicas de reflexión, construcción de secciones estructurales balanceadas, y métodos geofísicos someros, para constatar el comportamiento en profundidad tanto de las estructuras geológicas identificadas en superficie como de las posibles fallas ciegas corticales involucradas.
En primer lugar, se realizó un relevamiento regional del área de estudio empleando imágenes satelitales multiespectrales LANDSAT y SENTINEL 2, que permitieron reconocer diferentes niveles de abanicos aluviales y terrazas fluviales cuaternarios. Mediante la determinación de diferentes indicadores morfométricos en modelos de elevación digital (MED), junto con observaciones de campo, fue posible identificar evidencias de deformación sobre dichos niveles cuaternarios que han sido relacionadas genéticamente con cuatro fallas neotectónicas. Tres de ellas (fallas Arias, El Quemado y Copo Quile) fueron seleccionadas para efectuar estudios de mayor detalle por medio de la aplicación de métodos de geofísica somera (tomografía eléctrica resistiva (ERT) y tomografía sísmica de refracción Sísmica (SRT)), que permitieron corroborar su existencia en profundidad, realizar inferencias geométricas y cinemáticas, y estimar la magnitud de la deformación reciente. Las fallas Arias y El Quemado fueron interpretadas como fallas inversas relacionadas con deslizamiento flexural interstratal, mientras que la falla Copo Quile se interpretó como una falla inversa ciega de bajo ángulo.También se realizó una interpretación conjunta de líneas sísmicas de reflexión y pozos exploratorios pertenecientes a áreas hidrocarburíferas de las cuencas de Choromoro y Metán con el fin de contextualizar las principales estructuras reconocidas en el marco estratigráfico y tectónico regional. Toda la información fue integrada en una sección estructural balanceada mediante técnicas de modelado cinemático. Dicho modelo permite inferir que la deformación cuaternaria reconocida está relacionada al desplazamiento del basamento a lo largo de un corrimiento ciego, responsable del levantamiento de la sierra de La Candelaria y el cerr Cantero. Asimismo, el modelo cinemático permite interpretar la ubicación aproximada de los principales niveles de despegue que controlan el estilo de deformación. El nivel de despegue más somero, que controla la deformación de la cobertura sedimentaria se encuentra a 4 km de profundidad, a 21 km se estima la presencia de otra zona de cizalla subhorizontal dentro del basamento.
Finalmente, a partir de la integración de todos los resultados obtenidos, se evaluó el potencial sismogénico de las fallas en la zona de estudio. Las fallas de primer orden que controlan la deformación en la zona son las responsables de los grandes terremotos. Mientras, las fallas Cuaternarias flexodeslizantes e inversas afectan solamente a la cobertura sedimentaria y serían estructuras de segundo orden que acomodan la deformación y fueron activadas durante el cuaternario con movimientos asísmicos y/o sísmicos de muy baja magnitud.
Estos resultados permiten inferir que el corrimiento La Candelaria constituye una fuente sismogénica potencial de importancia para la región, donde se ubican numerosas poblaciones y obras civiles de envergadura. Por otra parte, la sección estructural balanceada implica la presencia de otras fallas ciegas de distinto orden de magnitud que podrían ser posibles fuentes sismogénicas profundas adicionales, marcando la necesidad de continuar con el desarrollo de este tipo de estudios en esta región tectónicamente activa.
Paleomagnetic dating of climatic events in Late Quaternary sediments of Lake Baikal (Siberia)
(2004)
Lake Baikal provides an excellent climatic archive for Central Eurasia as global climatic variations are continuously depicted in its sediments. We performed continuous rock magnetic and paleomagnetic analyses on hemipelagic sequences retrieved from 4 underwater highs reaching back 300 ka. The rock magnetic study combined with TEM, XRD, XRF and geochemical analyses evidenced that a magnetite of detrital origin dominates the magnetic signal in glacial sediments whereas interglacial sediments are affected by early diagenesis. HIRM roughly quantifies the hematite and goethite contributions and remains the best proxy for estimating the detrital input in Lake Baikal. Relative paleointensity records of the earth′s magnetic field show a reproducible pattern, which allows for correlation with well-dated reference curves and thus provides an alternative age model for Lake Baikal sediments. Using the paleomagnetic age model we observed that cooling in the Lake Baikal region and cooling of the sea surface water in the North Atlantic, as recorded in planktonic foraminifera δ18 O, are coeval. On the other hand, benthic δ18 O curves record mainly the global ice volume change, which occurs later than the sea surface temperature change. This proves that a dating bias results from an age model based on the correlation of Lake Baikal sedimentary records with benthic δ18 O curves. The compilation of paleomagnetic curves provides a new relative paleointensity curve, “Baikal 200”. With a laser-assisted grain size analysis of the detrital input, three facies types, reflecting different sedimentary dynamics can be distinguished. (1) Glacial periods are characterised by a high clay content mostly due to wind activity and by occurrence of a coarse fraction (sand) transported over the ice by local winds. This fraction gives evidence for aridity in the hinterland. (2) At glacial/interglacial transitions, the quantity of silt increases as the moisture increases, reflecting increased sedimentary dynamics. Wind transport and snow trapping are the dominant process bringing silt to a hemipelagic site (3) During the climatic optimum of the Eemian, the silt size and quantity are minimal due to blanketing of the detrital sources by the vegetal cover.
El flanco oriental de los Andes Centrales en el noroeste argentino es una zona caracterizada por serranías limitadas por fallas inversas que conforman un orógeno de piel gruesa activo con un patrón espacio-temporal no sistemático de deformación contraccional. Este patrón queda representado tanto por la dispersión de la actividad sísmica cortical como de la localización de las estructuras cuaternarias a través de la Cordillera Oriental y el Sistema de Santa Bárbara, configurando un frente orogénico difuso de más de 200 km de extensión. El estudio de la actividad neotectónica en esta región ha tomado más relevancia en los últimos años, mediante la aplicación de herramientas variadas, incluyendo técnicas de geomorfología tectónica, herramientas de teledetección, geodesia y estudios de campo convencionales. Los depósitos lacustres han demostrado ser, en numerosos ejemplos, excelentes marcadores de la actividad tectónica, dadas la horizontalidad original de sus capas y la susceptibilidad a los cambios del entorno. Es por ello que en este trabajo se analizaron los depósitos lacustres que afloran en el sector central de los valles Calchaquíes (región de Cafayate), para comprender cómo se acomoda la deformación cuaternaria en una de las cuencas intermontanas de la cuña orogénica activa.
El rumbo de las estructuras cuaternarias en el área de estudio es subparalelo al de las fallas que exhuman los cordones serranos circundantes. A partir del estudio estratigráfico, morfotectónico y estructural de los depósitos lacustres, se identificó un mínimo de cinco episodios de deformación afectando a la columna estratigráfica cuaternaria. Integrando perfiles estructurales balanceados con edades obtenidas en este trabajo y recopiladas de la bibliografía, se calcularon para el Pleistoceno mediotardío, tasas mínimas y máximas de acortamiento que varían entre 0,19-2,80 y 0,21-4,47 mm/a, respectivamente. Para comparar estos resultados con mediciones de la tectónica activa a escala regional se recopilaron datos de estaciones geodésicas del noroeste argentino, con los cuales se elaboró un perfil de velocidades horizontales. El perfil obtenido muestra un decrecimiento gradual de los vectores hacia el este, indicando actividad interna del orógeno en congruencia con los registros de actividad sísmica y compilación regional de las estructuras cuaternarias.
Además de la caracterización neotectónica de este sector de la Cordillera Oriental, el análisis estratigráfico de los depósitos lacustres ha permitido refinar la evolución geológica del sector central de los valles Calchaquíes durante el Cuaternario. De esta manera se han identificado al menos siete episodios de inundación lacustre relacionados con la desconexión del sistema fluvial con su nivel de base, dando lugar a sucesivos eventos de agradación y erosión. Las cotas máximas alcanzadas por los paleolagos, en conjunto con un modelo hidrológico previamente publicado para esta región, permitieron asimismo efectuar una comparación con el registro paleoclimático regional.
Los resultados de esta tesis representan un aporte significativo al conocimiento de la evolución tectónica y estratigráfica del sector central de los valles Calchaquíes durante el Cuaternario. Por otra parte, su integración a escala regional contribuye a comprender mejor la dinámica de la deformación en la cuña orogénica de piel gruesa del noroeste argentino.
Paleoenvironmental records provide ample information on the Late Quaternary climatic evolution. Due to the great diversity of continental mid-latitude environments the synthetic picture of the past mid-latitudinal climate changes is, however, far from being complete. Owing to its significant size and landlocked setting the Black Sea constitutes a perfect location to study patterns and mechanisms of climate change along the continental interior of Central and Eastern Europe and Asia Minor. Presently, the southern drainage area of the Black Sea is characterized by a Mediterranean-type climate while the northern drainage is under the influence of Central and Northern European climate. During the Last Glacial a decrease in the global sea level disconnected the Black Sea from the Mediterranean Sea transforming it into a giant closed lake. At that time atmospheric precipitation and related with it river run-off were the most important factors driving sediment supply and water chemistry of the Black ‘Lake’. Therefore studying properties of the Black Sea sediments provides important information on the interactions and development of the Mediterranean and Central and North European climate in the past. One significant outcome of my thesis is an improved chronostraphigraphical framework for the glacial lacustrine unit of the Black Sea sediment cores, which allowed to refine the environmental history of the Black Sea region and enabled a reliable correlation with data from other marine and terrestrial archives. Data gathered along a N-S transect presented on a common time scale revealed coherent changes in the basin and its surrounding. During the glacial, the southward-shifted Polar Front reduced moisture transport to the northern drainage of the Black Sea and let the southern drainage become dominant in freshwater and sediment supply into the basin. Changes in NW Anatolian precipitation reconstructed from the variability of the terrigenous input imply that during the glacial the regional rainfall variability was strongly influenced by Mediterranean sea surface temperatures and decreased in response to the cooling associated with the North Atlantic Heinrich Events H1 and H2. In contrast to regional precipitation changes, the hydrological properties of the Black Sea remained relatively stable under full glacial conditions. First significant modification in the freshwater/sediment sources reconstructed from changes in the sediment composition, lithology, and 18O of ostracods took place at around 16.4 cal ka BP, simultaneous to the early deglacial northward retreat of the oceanic and atmospheric polar fronts. Meltwater pulses, most probably derived from the disintegrating European ice sheets, changed the isotopic composition of the Black Sea and increased the supply from northern sediment sources. While these changes signalized a mitigation of the Northern European and Mediterranean climate, a decisive increase in local temperature was indicated only later at the transition from the Oldest Dryas to the Bølling around 14.6 cal ka BP. At that time the warming of the Black Sea surface initiated massive phytoplankton blooms, which in turn, induced the precipitation of inorganic carbonates. This biologically triggered process significantly changed the water chemistry and was recorded by simultaneous shifts in the elemental composition of ostracod shells and in the isotopic composition of the inorganically-precipitated carbonates. Starting with the B/A warming and continuing through the YD cold interval and the Early Holocene warming, the Black Sea temperature signal corresponds to the precipitation and temperature changes recorded in the wider Mediterranean region. Early Holocene conditions, similar to those of the Bølling/Allerød, were punctured by the marine inflow from the Mediterranean at ~ 9.3 cal ka BP, which terminated the lacustrine phase of the Black Sea and had a substantial impact on the chemical and physical properties of its water.
The Arctic is changing rapidly and permafrost is thawing. Especially ice-rich permafrost, such as the late Pleistocene Yedoma, is vulnerable to rapid and deep thaw processes such as surface subsidence after the melting of ground ice. Due to permafrost thaw, the permafrost carbon pool is becoming increasingly accessible to microbes, leading to increased greenhouse gas emissions, which enhances the climate warming.
The assessment of the molecular structure and biodegradability of permafrost organic matter (OM) is highly needed. My research revolves around the question “how does permafrost thaw affect its OM storage?” More specifically, I assessed (1) how molecular biomarkers can be applied to characterize permafrost OM, (2) greenhouse gas production rates from thawing permafrost, and (3) the quality of OM of frozen and (previously) thawed sediments.
I studied deep (max. 55 m) Yedoma and thawed Yedoma permafrost sediments from Yakutia (Sakha Republic). I analyzed sediment cores taken below thermokarst lakes on the Bykovsky Peninsula (southeast of the Lena Delta) and in the Yukechi Alas (Central Yakutia), and headwall samples from the permafrost cliff Sobo-Sise (Lena Delta) and the retrogressive thaw slump Batagay (Yana Uplands). I measured biomarker concentrations of all sediment samples. Furthermore, I carried out incubation experiments to quantify greenhouse gas production in thawing permafrost.
I showed that the biomarker proxies are useful to assess the source of the OM and to distinguish between OM derived from terrestrial higher plants, aquatic plants and microbial activity. In addition, I showed that some proxies help to assess the degree of degradation of permafrost OM, especially when combined with sedimentological data in a multi-proxy approach. The OM of Yedoma is generally better preserved than that of thawed Yedoma sediments. The greenhouse gas production was highest in the permafrost sediments that thawed for the first time, meaning that the frozen Yedoma sediments contained most labile OM. Furthermore, I showed that the methanogenic communities had established in the recently thawed sediments, but not yet in the still-frozen sediments.
My research provided the first molecular biomarker distributions and organic carbon turnover data as well as insights in the state and processes in deep frozen and thawed Yedoma sediments. These findings show the relevance of studying OM in deep permafrost sediments.
This dissertation was carried out as part of the international and interdisciplinary graduate school StRATEGy. This group has set itself the goal of investigating geological processes that take place on different temporal and spatial scales and have shaped the southern central Andes. This study focuses on claystones and carbonates of the Yacoraite Fm. that were deposited between Maastricht and Dan in the Cretaceous Salta Rift Basin. The former rift basin is located in northwest Argentina and is divided into the sub-basins Tres Cruces, Metán-Alemanía and Lomas de Olmedo. The overall motivation for this study was to gain new knowledge about the evolution of marine and lacustrine conditions during the Yacoraite Fm. Deposit in the Tres Cruces and Metán-Alemanía sub-basins. Other important aspects that were examined within the scope of this dissertation are the conversion of organic matter from Yacoraite Fm. into oil and its genetic relationship to selected oils produced and natural oil spills. The results of my study show that the Yacoraite Fm. began to be deposited under marine conditions and that a lacustrine environment developed by the end of the deposition in the Tres Cruces and Metán-Alemanía Basins. In general, the kerogen of Yacoraite Fm. consists mainly of the kerogen types II, III and II / III mixtures. Kerogen type III is mainly found in samples from the Yacoraite Fm., whose TOC values are low. Due to the adsorption of hydrocarbons on the mineral surfaces (mineral matrix effect), the content of type III kerogen with Rock-Eval pyrolysis in these samples could be overestimated. Investigations using organic petrography show that the organic particles of Yacoraite Fm. mainly consist of alginites and some vitrinite-like particles. The pyrolysis GC of the rock samples showed that the Yacoraite Fm. generates low-sulfur oils with a predominantly low-wax, paraffinic-naphthenic-aromatic composition and paraffinic wax-rich oils. Small proportions of paraffinic, low-wax oils and a gas condensate-generating facies are also predicted. Here, too, mineral matrix effects were taken into account, which can lead to a quantitative overestimation of the gas-forming character.
The results of an additional 1D tank modeling carried out show that the beginning (10% TR) of the oil genesis took place between ≈10 Ma and ≈4 Ma. Most of the oil (from ≈50% to 65%) was generated prior to the development of structural traps formed during the Plio-Pleistocene Diaguita deformation phase. Only ≈10% of the total oil generated was formed and potentially trapped after the formation of structural traps. Important factors in the risk assessment of this petroleum system, which can determine the small amounts of generated and migrated oil, are the generally low TOC contents and the variable thickness of the Yacoraite Fm. Additional risks are associated with a low density of information about potentially existing reservoir structures and the quality of the overburden.
The transfer of particulate organic carbon from continents to the ocean is an important component of the global carbon cycle. Transfer to and burial of photosynthetically fixed biospheric organic carbon in marine sediments can effectively sequester atmospheric carbon dioxide over geological timescales. The exhumation and erosion of fossil organic carbon contained in sedimentary rocks, i.e. petrogenic carbon, can result in remineralization, releasing carbon to the atmosphere. In contrast, eroded petrogenic organic carbon that gets transferred back to the ocean and reburied does not affect atmospheric carbon content.
Mountain ranges play a key role in this transfer since they can source vast amounts of sediment including particulate organic carbon. Globally, the export of both, biospheric and petrogenic organic carbon has been linked to sediment export. Additionally, short transfer times from mountains to the ocean and high sediment concentrations have been shown to increase the likelihood of organic carbon burial. While the importance of mountain ranges in the organic carbon cycle is now widely recognized, the processes acting within mountain ranges to influence the storage, cycling and mobilization of organic carbon, as well as carbon fluxes from mountain ranges remain poorly constrained.
In this thesis, I employ different methods to assess the nature and fate of particulate organic carbon in mountain belts, ranging from the molecular to regional landscape scale. These studies are located along the Trans-Himalayan Kali Gandaki River in Central Nepal. This river traverses all major geological and climatic zones of the Himalaya, from the dry northern Tibetan plateau to the high-relief, monsoon dominated steep High Himalaya and the lower relief and abundant vegetation of the Lesser Himalayan region.
First, I document how biospheric organic matter has accumulated during the Holocene in the headwaters of the Kali Gandaki River valley, by combining compound specific isotope measurements with different dating methods and grain size data, and investigate the stability of this organic carbon reservoir on millennial timescales. I show, that around 1.6 ka an eco-geomorphic tipping point occurred leading to a destabilization of the landscape resulting in today’s high erosion rates and the excavation of the aged organic carbon reservoir. This study highlights the climatic and geomorphic controls on biospheric organic carbon storage and release from mountain ranges.
Second, I systematically investigate the spatial variation of particulate organic carbon fluxes across the Himalaya along the Kali Gandaki River, using bulk stable and radioactive isotopes combined with a new Bayesian modeling approach. The detailed dataset allows the distinction of aged and modern biospheric organic carbon as well as petrogenic organic carbon across the Himalayan mountain range and the investigation of the role of climatic and geomorphic factors in their riverine export. The data suggest a decoupling of the particulate organic carbon from the sediment yield along the Kali Gandaki River, partially driven by climatic and geomorphic processes. In contrast to the suspended sediment, a large part of the particulate organic carbon exported by the river originates from the Tibetan part of the catchment and is dominated by petrogenic organic carbon derived from Jurassic shales with only minor contributions of modern and aged biospheric organic carbon. These findings emphasize the importance of organic carbon source distribution and erosion mechanisms in determining the organic carbon export from mountain ranges.
In a third step, I explore the potential of ultra-high resolution mass spectrometry for particulate organic carbon transport studies. I have generated a novel and unprecedented high-resolution molecular dataset, which contains up to 103 molecular formulas of the lipid fraction of particulate organic matter for modern and aged biospheric carbon, petrogenic organic carbon and river sediments. First, I test if this dataset can be used to better resolve different organic carbon sources and to identify new geochemical tracers. Using multivariate statistics, I identify up to 10² characteristic molecular formulas for the major organic carbon sources in the upper part of the Kali Gandaki catchment, and trace their transfer from the surrounding landscape into the river sediment. Second, I test the potential of the molecular dataset to trace molecular transformations along source-to-sink pathways. I identify changes in molecular metrics derived from the dataset, which are characteristic of transformation processes during incorporation of litter into soil, the aging of soil material, and the mobilization of the organic carbon into the river. These two studies demonstrate that high-resolution molecular datasets open a promising analytical window on particulate organic carbon and can provide novel insights into the composition, sourcing and transformation of riverine particulate organic carbon.
Collectively, these studies advance our understanding of the processes contributing to the storage and mobilization of organic carbon in the Central Himalaya, the mountain belt that dominates global erosional fluxes. They do so by identifying the major sources of particulate organic carbon to the Trans-Himalayan Kali Gandaki River, by elucidating their sensitivity to climate and geomorphic processes, and by identifying some of the transformations of this material on the molecular scale. As a result, the thesis demonstrates that the amount and composition of organic carbon routed from mountain belts is a function of the dynamic interactions of geologic, biologic, geomorphic and climatic processes within the mountain belt. This understanding will ultimately help in answering whether the build-up and erosion of mountain ranges over geological time represents a net carbon source or sink to the atmosphere. Beyond this, the thesis contributes to our technical ability to characterize organic matter and attribute it to sources by scoping the potential of high-end molecular analysis.
Das Parallel-Seismik-Verfahren dient vor allem der nachträglichen Längenmessung von Fundamentpfählen oder ähnlichen Elementen zur Gründung von Bauwerken. Eine solche Messung wird beispielsweise notwendig, wenn ein Gebäude verstärkt, erhöht oder anders als bisher genutzt werden soll, aber keine Unterlagen mehr über die Fundamente vorhanden sind. Das Messprinzip des schon seit einigen Jahrzehnten bekannten Verfahrens ist relativ einfach: Auf dem Pfahlkopf wird meist durch Hammerschlag eine Stoßwelle erzeugt, die durch den Pfahl nach unten läuft. Dabei wird Energie in den Boden abgegeben. Die abgestrahlten Wellen werden von Sensoren in einem parallel zum Pfahl hergestellten Bohrloch registriert. Aus den Laufzeiten lassen sich die materialspezifischen Wellengeschwindigkeiten im Pfahl und im Boden sowie die Pfahllänge ermitteln. Bisher wurde meist ein sehr einfaches Verfahren zur Datenauswertung verwendet, das die Länge der Pfähle systematisch überschätzt. In der vorliegenden Dissertation wurden die mathematisch-physikalischen Grundlagen beleuchtet und durch Computersimulation die Wellenausbreitung in Pfahl und Boden genau untersucht. Weitere Simulationen klärten den Einfluss verschiedener Mess- und Strukturparameter, beispielsweise den Einfluss von Bodenschichtung oder Fehlstellen im Pfahl. So konnte geklärt werden, in welchen Fällen mit dem Parallel-Seismik-Verfahren gute Ergebnisse erzielt werden können (z. B. bei Fundamenten in Sand oder Ton) und wo es an seine Grenzen stößt (z. B. bei Gründung im Fels). Auf Basis dieser Ergebnisse entstand ein neuer mathematischer Formalismus zur Auswertung der Laufzeiten. In Verbindung mit einem Verfahren zur Dateninversion, d. h. der automatischen Anpassung der Unbekannten in den Gleichungen an die Messergebnisse, lassen sich sehr viel genauere Werte für die Pfahllänge ermitteln als mit allen bisher publizierten Verfahren. Zudem kann man nun auch mit relativ großen Abständen zwischen Bohrloch und Pfahl (2 - 3 m) arbeiten. Die Methode wurde an simulierten Daten ausführlich getestet. Die Messmethode und das neue Auswerteverfahren wurden in einer Reihe praktischer Anwendungen getestet – und dies fast immer erfolgreich. Nur in einem Fall komplizierter Fundamentgeometrie bei gleichzeitig sehr hoher Anforderung an die Genauigkeit war schon nach Simulationen klar, dass hier ein Einsatz nicht sinnvoll ist. Dafür zeigte es sich, dass auch die Länge von Pfahlwänden und Spundwänden ermittelt werden kann. Die Parallel-Seismik-Methode funktioniert als einziges verfügbares Verfahren zur Fundamentlängenermittlung zugleich in den meisten Bodenarten sowie an metallischen und nichtmetallischen Fundamenten und kommt ohne Kalibrierung aus. Sie ist nun sehr viel breiter einsetzbar und liefert sehr viel genauere Ergebnisse. Die Simulationen zeigten noch Potential für Erweiterungen, zum Beispiel durch den Einsatz spezieller Sensoren, die zusätzliche Wellentypen empfangen und unterscheiden können.
Large parts of the Earth’s interior are inaccessible to direct observation, yet global geodynamic processes are governed by the physical material properties under extreme pressure and temperature conditions. It is therefore essential to investigate the deep Earth’s physical properties through in-situ laboratory experiments. With this goal in mind, the optical properties of mantle minerals at high pressure offer a unique way to determine a variety of physical properties, in a straight-forward, reproducible, and time-effective manner, thus providing valuable insights into the physical processes of the deep Earth. This thesis focusses on the system Mg-Fe-O, specifically on the optical properties of periclase (MgO) and its iron-bearing variant ferropericlase ((Mg,Fe)O), forming a major planetary building block. The primary objective is to establish links between physical material properties and optical properties. In particular the spin transition in ferropericlase, the second-most abundant phase of the lower mantle, is known to change the physical material properties. Although the spin transition region likely extends down to the core-mantle boundary, the ef-fects of the mixed-spin state, where both high- and low-spin state are present, remains poorly constrained.
In the studies presented herein, we show how optical properties are linked to physical properties such as electrical conductivity, radiative thermal conductivity and viscosity. We also show how the optical properties reveal changes in the chemical bonding. Furthermore, we unveil how the chemical bonding, the optical and other physical properties are affected by the iron spin transition. We find opposing trends in the pres-sure dependence of the refractive index of MgO and (Mg,Fe)O. From 1 atm to ~140 GPa, the refractive index of MgO decreases by ~2.4% from 1.737 to 1.696 (±0.017). In contrast, the refractive index of (Mg0.87Fe0.13)O (Fp13) and (Mg0.76Fe0.24)O (Fp24) ferropericlase increases with pressure, likely because Fe Fe interactions between adjacent iron sites hinder a strong decrease of polarizability, as it is observed with increasing density in the case of pure MgO. An analysis of the index dispersion in MgO (decreasing by ~23% from 1 atm to ~103 GPa) reflects a widening of the band gap from ~7.4 eV at 1 atm to ~8.5 (±0.6) eV at ~103 GPa. The index dispersion (between 550 and 870 nm) of Fp13 reveals a decrease by a factor of ~3 over the spin transition range (~44–100 GPa). We show that the electrical band gap of ferropericlase significantly widens up to ~4.7 eV in the mixed spin region, equivalent to an increase by a factor of ~1.7. We propose that this is due to a lower electron mobility between adjacent Fe2+ sites of opposite spin, explaining the previously observed low electrical conductivity in the mixed spin region. From the study of absorbance spectra in Fp13, we show an increasing covalency of the Fe-O bond with pressure for high-spin ferropericlase, whereas in the low-spin state a trend to a more ionic nature of the Fe-O bond is observed, indicating a bond weakening effect of the spin transition. We found that the spin transition is ultimately caused by both an increase of the ligand field-splitting energy and a decreasing spin-pairing energy of high-spin Fe2+.
Growing populations, continued economic development, and limited natural resources are critical factors affecting sustainable development. These factors are particularly pertinent in developing countries in which large parts of the population live at a subsistence level and options for sustainable development are limited. Therefore, addressing sustainable land use strategies in such contexts requires that decision makers have access to evidence-based impact assessment tools that can help in policy design and implementation. Ex-ante impact assessment is an emerging field poised at the science-policy interface and is used to assess the potential impacts of policy while also exploring trade-offs between economic, social and environmental sustainability targets. The objective of this study was to operationalise the impact assessment of land use scenarios in the context of developing countries that are characterised by limited data availability and quality. The Framework for Participatory Impact Assessment (FoPIA) was selected for this study because it allows for the integration of various sustainability dimensions, the handling of complexity, and the incorporation of local stakeholder perceptions. FoPIA, which was originally developed for the European context, was adapted to the conditions of developing countries, and its implementation was demonstrated in five selected case studies. In each case study, different land use options were assessed, including (i) alternative spatial planning policies aimed at the controlled expansion of rural-urban development in the Yogyakarta region (Indonesia), (ii) the expansion of soil and water conservation measures in the Oum Zessar watershed (Tunisia), (iii) the use of land conversion and the afforestation of agricultural areas to reduce soil erosion in Guyuan district (China), (iv) agricultural intensification and the potential for organic agriculture in Bijapur district (India), and (v) land division and privatisation in Narok district (Kenya). The FoPIA method was effectively adapted by dividing the assessment into three conceptual steps: (i) scenario development; (ii) specification of the sustainability context; and (iii) scenario impact assessment. A new methodological approach was developed for communicating alternative land use scenarios to local stakeholders and experts and for identifying recommendations for future land use strategies. Stakeholder and expert knowledge was used as the main sources of information for the impact assessment and was complemented by available quantitative data. Based on the findings from the five case studies, FoPIA was found to be suitable for implementing the impact assessment at case study level while ensuring a high level of transparency. FoPIA supports the identification of causal relationships underlying regional land use problems, facilitates communication among stakeholders and illustrates the effects of alternative decision options with respect to all three dimensions of sustainable development. Overall, FoPIA is an appropriate tool for performing preliminary assessments but cannot replace a comprehensive quantitative impact assessment, and FoPIA should, whenever possible, be accompanied by evidence from monitoring data or analytical tools. When using FoPIA for a policy oriented impact assessment, it is recommended that the process should follow an integrated, complementary approach that combines quantitative models, scenario techniques, and participatory methods.
The Central Andes host large reserves of base and precious metals. The region represented, in 2017, an important part of the worldwide mining activity. Three principal types of deposits have been identified and studied: 1) porphyry type deposits extending from central Chile and Argentina to Bolivia, and Northern Peru, 2) iron oxide-copper-gold (IOCG) deposits, extending from central Peru to central Chile, and 3) epithermal tin polymetallic deposits extending from Southern Peru to Northern Argentina, which compose a large part of the deposits of the Bolivian Tin Belt (BTB). Deposits in the BTB can be divided into two major types: (1) tin-tungsten-zinc pluton-related polymetallic deposits, and (2) tin-silver-lead-zinc epithermal polymetallic vein deposits.
Mina Pirquitas is a tin-silver-lead-zinc epithermal polymetallic vein deposit, located in north-west Argentina, that used to be one of the most important tin-silver producing mine of the country. It was interpreted to be part of the BTB and it shares similar mineral associations with southern pluton related BTB epithermal deposits. Two major mineralization events related to three pulses of magmatic fluids mixed with meteoric water have been identified. The first event can be divided in two stages: 1) stage I-1 with quartz, pyrite, and cassiterite precipitating from fluids between 233 and 370 °C and salinity between 0 and 7.5 wt%, corresponding to a first pulse of fluids, and 2) stage I-2 with sphalerite and tin-silver-lead-antimony sulfosalts precipitating from fluids between 213 and 274 °C with salinity up to 10.6 wt%, corresponding to a new pulse of magmatic fluids in the hydrothermal system. The mineralization event II deposited the richest silver ores at Pirquitas. Event II fluids temperatures and salinities range between 190 and 252 °C and between 0.9 and 4.3 wt% respectively. This corresponds to the waning supply of magmatic fluids. Noble gas isotopic compositions and concentrations in ore-hosted fluid inclusions demonstrate a significant contribution of magmatic fluids to the Pirquitas mineralization although no intrusive rocks are exposed in the mine area.
Lead and sulfur isotopic measurements on ore minerals show that Pirquitas shares a similar signature with southern pluton related polymetallic deposits in the BTB. Furthermore, the major part of the sulfur isotopic values of sulfide and sulfosalt minerals from Pirquitas ranges in the field for sulfur derived from igneous rocks. This suggests that the main contribution of sulfur to the hydrothermal system at Pirquitas is likely to be magma-derived. The precise age of the deposit is still unknown but the results of wolframite dating of 2.9 ± 9.1 Ma and local structural observations suggest that the late mineralization event is younger than 12 Ma.
To what extent cities can be made sustainable under the mega-trends of urbanization and climate change remains a matter of unresolved scientific debate. Our inability in answering this question lies partly in the deficient knowledge regarding pivotal humanenvironment interactions. Regarded as the most well documented anthropogenic climate modification, the urban heat island (UHI) effect – the warmth of urban areas relative to the rural hinterland – has raised great public health concerns globally. Worse still, heat waves are being observed and are projected to increase in both frequency and intensity, which further impairs the well-being of urban dwellers. Albeit with a substantial increase in the number of publications on UHI in the recent decades, the diverse urban-rural definitions applied in previous studies have remarkably hampered the general comparability of results achieved. In addition, few studies have attempted to synergize the land use data and thermal remote sensing to systematically assess UHI and its contributing factors.
Given these research gaps, this work presents a general framework to systematically quantify the UHI effect based on an automated algorithm, whereby cities are defined as clusters of maximum spatial continuity on the basis of land use data, with their rural hinterland being defined analogously. By combining land use data with spatially explicit surface skin temperatures from satellites, the surface UHI intensity can be calculated in a consistent and robust manner. This facilitates monitoring, benchmarking, and categorizing UHI intensities for cities across scales. In light of this innovation, the relationship between city size and UHI intensity has been investigated, as well as the contributions of urban form indicators to the UHI intensity.
This work delivers manifold contributions to the understanding of the UHI, which have complemented and advanced a number of previous studies. Firstly, a log-linear relationship between surface UHI intensity and city size has been confirmed among the 5,000 European cities. The relationship can be extended to a log-logistic one, when taking a wider range of small-sized cities into account. Secondly, this work reveals a complex interplay between UHI intensity and urban form. City size is found to have the strongest influence on the UHI intensity, followed by the fractality and the anisometry. However, their relative contributions to the surface UHI intensity depict a pronounced regional heterogeneity, indicating the importance of considering spatial patterns of UHI while implementing UHI adaptation measures.
Lastly, this work presents a novel seasonality of the UHI intensity for individual clusters in the form of hysteresis-like curves, implying a phase shift between the time series of UHI intensity and background temperatures. Combining satellite observation and urban boundary layer simulation, the seasonal variations of UHI are assessed from both screen and skin levels. Taking London as an example, this work ascribes the discrepancies between the seasonality observed at different levels mainly to the peculiarities of surface skin temperatures associated with the incoming solar radiation. In addition, the efforts in classifying cities according to their UHI characteristics highlight the important role of regional climates in determining the UHI.
This work serves as one of the first studies conducted to systematically and statistically scrutinize the UHI. The outcomes of this work are of particular relevance for the overall spatial planning and regulation at meso- and macro levels in order to harness the benefits of rapid urbanization, while proactively minimizing its ensuing thermal stress.
Natural and potentially hazardous events occur on the Earth’s surface every day. The most destructive of these processes must be monitored, because they may cause loss of lives, infrastructure, and natural resources, or have a negative effect on the environment. A variety of remote sensing technologies allow the recoding of data to detect these processes in the first place, partly based on the diagnostic landforms that they form. To perform this effectively, automatic methods are desirable.
Universal detection of natural hazards is challenging due to their differences in spatial impacts, timing and longevity of consequences, and the spatial resolution of remote-sensing data. Previous studies have reported that topographic metrics such as roughness, which can be captured from digital elevation data, can reveal landforms diagnostic of natural hazards, such as gullies, dunes, lava fields, landslides and snow avalanches, as these landforms tend to be more heterogeneous than the surrounding landscape. A single roughness metric is often limited in such detections; however, a more complex approach that exploits the spatial relation and the location of objects, such as object-based image analysis (OBIA), is desirable.
In this thesis, I propose a topographic roughness measure derived from an airborne laser scanning (ALS) digital terrain model (DTM) and discuss its performance in detecting landforms principally diagnostic of natural hazards. I further develop OBIA-based algorithms for the detection of snow avalanches using near-infrared (NIR) aerial images, and the size (changes) of mountain lakes using LANDSAT satellite images. I quantitatively test and document how the level of difficulty in detecting these very challenging landforms depends on the input data resolution, the derivatives that could be evaluated from images and DTMs, the size, shape and complexity of landforms, and the capabilities of obtaining the information in the data. I demonstrate that surface roughness is a promising metric for detecting different landforms in diverse environments, and that OBIA assists significantly in detecting parts of lakes and snow avalanches that may not be correctly assigned by applying only the thresholding of spectral properties of data and their derivatives.
The curvature-based surface roughness parameter allows the detection of gullies, dunes, lava fields and landslides with a user’s accuracy of 0.63, 0.21, 0.53, and 0.45, respectively. The OBIA algorithms for detecting lakes and snow avalanches obtained user’s accuracy of 0.98, and 0.78, respectively. Most of the analysed landforms constituted only a small part of the entire dataset, and therefore the user’s accuracy is the most appropriate performance measure that should be given in a such classification, because it tells how many automatically-extracted pixels in fact represent the object that one wants to classify, and its calculation does not take the second (background) class into account. One advantage of the proposed roughness parameter is that it allows the extraction of the heterogeneity of the surface without the need for data detrending. The OBIA approach is novel in that it allows the classification of lakes regardless of the physical state of their water, and also allows the separation of frozen lakes from glaciers that have very similar water indices used in purely optical remote sensing applications. The algorithm proposed for snow avalanches allows the detection of release zones, tracks, and deposition zones by verifying the snow heterogeneity based on a roughness metric evaluated from a water index, and by analysing the local relation of segments with their neighbouring objects. This algorithm contains few steps, which allows for the simultaneous classification of avalanches that occur on diverse mountain slopes and differ in size and shape.
This thesis contributes to natural hazard research as it provides automatic solutions to tracking six different landforms that are diagnostic of natural hazards over large regions. This is a step toward delineating areas susceptible to the processes producing these landforms and the improvement of hazard maps.
Due to the major role of greenhouse gas emissions in global climate change, the development of non-fossil energy technologies is essential. Deep geothermal energy represents such an alternative, which offers promising properties such as a high base load capability and a large untapped potential. The present work addresses barite precipitation within geothermal systems and the associated reduction in rock permeability, which is a major obstacle to maintaining high efficiency. In this context, hydro-geochemical models are essential to quantify and predict the effects of precipitation on the efficiency of a system.
The objective of the present work is to quantify the induced injectivity loss using numerical and analytical reactive transport simulations. For the calculations, the fractured-porous reservoirs of the German geothermal regions North German Basin (NGB) and Upper Rhine Graben (URG) are considered.
Similar depth-dependent precipitation potentials could be determined for both investigated regions (2.8-20.2 g/m3 fluid). However, the reservoir simulations indicate that the injectivity loss due to barite deposition in the NGB is significant (1.8%-6.4% per year) and the longevity of the system is affected as a result; this is especially true for deeper reservoirs (3000 m). In contrast, simulations of URG sites indicate a minor role of barite (< 0.1%-1.2% injectivity loss per year). The key differences between the investigated regions are reservoir thicknesses and the presence of fractures in the rock, as well as the ionic strength of the fluids. The URG generally has fractured-porous reservoirs with much higher thicknesses, resulting in a greater distribution of precipitates in the subsurface. Furthermore, ionic strengths are higher in the NGB, which accelerates barite precipitation, causing it to occur more concentrated around the wellbore. The more concentrated the precipitates occur around the wellbore, the higher the injectivity loss.
In this work, a workflow was developed within which numerical and analytical models can be used to estimate and quantify the risk of barite precipitation within the reservoir of geothermal systems. A key element is a newly developed analytical scaling score that provides a reliable estimate of induced injectivity loss. The key advantage of the presented approach compared to fully coupled reservoir simulations is its simplicity, which makes it more accessible to plant operators and decision makers. Thus, in particular, the scaling score can find wide application within geothermal energy, e.g., in the search for potential plant sites and the estimation of long-term efficiency.
Underground coal gasification (UCG) has the potential to increase worldwide coal reserves by developing coal resources, currently not economically extractable by conventional mining methods. For that purpose, coal is combusted in situ to produce a high-calorific synthesis gas with different end-use options, including electricity generation as well as production of fuels and chemical feedstock. Apart from the high economic potentials, UCG may induce site‐specific environmental impacts, including ground surface subsidence and pollutant migration of UCG by-products into shallow freshwater aquifers. Sustainable and efficient UCG operation requires a thorough understanding of the coupled thermal, hydraulic and mechanical processes, occurring in the UCG reactor vicinity. The development and infrastructure costs of UCG trials are very high; therefore, numerical simulations of coupled processes in UCG are essential for the assessment of potential environmental impacts. Therefore, the aim of the present study is to assess UCG-induced permeability changes, potential hydraulic short circuit formation and non-isothermal multiphase fluid flow dynamics by means of coupled numerical simulations. Simulation results on permeability changes in the UCG reactor vicinity demonstrate that temperature-dependent thermo-mechanical parameters have to be considered in near-field assessments, only. Hence, far-field simulations do not become inaccurate, but benefit from increased computational efficiency when thermo-mechanical parameters are maintained constant. Simulations on potential hydraulic short circuit formation between single UCG reactors at regional-scale emphasize that geologic faults may induce hydraulic connections, and thus compromise efficient UCG operation. In this context, the steam jacket surrounding high-temperature UCG reactors plays a vital role in avoiding UCG by-products escaping into freshwater aquifers and in minimizing energy consumption by formation fluid evaporation. A steam jacket emerges in the close reactor vicinity due to phase transition of formation water and is a non-isothermal flow phenomenon. Considering this complex multiphase flow behavior, an innovative conceptual modeling approach, validated against field data, enables the quantification and prediction of UCG reactor water balances. The findings of this doctoral thesis provide an important basis for integration of thermo-hydro-mechanical simulations in UCG, required for the assessment and mitigation of its potential environmental impacts as well as optimization of its efficiency.
Magnetotellurics (MT) is a geophysical method that is able to image the electrical conductivity structure of the subsurface by recording time series of natural electromagnetic (EM) field variations. During the data processing these time series are divided into small segments and for each segment spectral values are computed which are typically averaged in a statistical manner to obtain MT transfer functions. Unfortunately, the presence of man-made EM noise sources often deteriorates a significant amount of the recorded time series resulting in disturbed transfer functions. Many advanced processing techniques, e.g. robust statistics, pre-stack data selection or remote reference, have been developed to tackle this problem. The first two techniques reduce the amount of outliers and noise in the data whereas the latter approach removes noise by using data from another MT station. However, especially in populated regions the data processing is still quite challenging even with these approaches. In this thesis, I present two novel pre-stack data confinement and selection criteria for the detection of outliers and noise affected data based on (i) a distance measure of each data segment with regard to the entire sample distribution and (ii) the evaluation of the magnetic polarisation direction of all segments. The first criterion is able to remove data points that scatter around the desired MT distribution and furthermore it can, under some circumstances, even reject complete data cluster originating from noise sources. The second criterion eliminates data points caused by a strongly polarised magnetic signal. Both criteria have been successfully applied to many stations with different noise contaminations showing that they can significantly improve the transfer function estimation. The novel criteria were used to evaluate a MT data set from the Eastern Karoo Basin in South Africa. The corresponding field experiment is part of an extensive research programme to collect information of the current e.g. geological setting in this region prior to a potential shale gas exploitation. The aim was to investigate whether a three-dimensional (3D) inversion of the newly measured data fosters a more realistic mapping of physical properties of the target horizon. For this purpose, a comprehensive 3D model was derived by using all available data. In a second step, I analysed parameters of the target horizon, e.g. its conductivity, that are proxies for physical properties such as thermal maturity and porosity.
The collision of bathymetric anomalies, such as oceanic spreading centers, at convergent plate margins can profoundly affect subduction dynamics, magmatism, and the structural and geomorphic evolution of the overriding plate. The Southern Patagonian Andes of South America are a prime example for sustained oceanic ridge collision and the successive formation and widening of an extensive asthenospheric slab window since the Middle Miocene. Several of the predicted upper-plate geologic manifestations of such deep-seated geodynamic processes have been studied in this region, but many topics remain highly debated. One of the main controversial topics is the interpretation of the regional low-temperature thermochronology exhumational record and its relationship with tectonic and/or climate-driven processes, ultimately manifested and recorded in the landscape evolution of the Patagonian Andes. The prominent along-strike variance in the topographic characteristics of the Andes, combined with coupled trends in low-temperature thermochronometer cooling ages have been interpreted in very contrasting ways, considering either purely climatic (i.e. glacial erosion) or geodynamic (slab-window related) controlling factors.
This thesis focuses on two main aspects of these controversial topics. First, based on field observations and bedrock low-temperature thermochronology data, the thesis addresses an existing research gap with respect to the neotectonic activity of the upper plate in response to ridge collision - a mechanism that has been shown to affect the upper plate topography and exhumational patterns in similar tectonic settings. Secondly, the qualitative interpretation of my new and existing thermochronological data from this region is extended by inverse thermal modelling to define thermal histories recorded in the data and evaluate the relative importance of surface vs. geodynamic factors and their possible relationship with the regional cooling record.
My research is centered on the Northern Patagonian Icefield (NPI) region of the Southern Patagonian Andes. This site is located inboard of the present-day location of the Chile Triple Junction - the juncture between the colliding Chile Rise spreading center and the Nazca and Antarctic Plates along the South American convergent margin. As such this study area represents the region of most recent oceanic-ridge collision and associated slab window formation. Importantly, this location also coincides with the abrupt rise in summit elevations and relief characteristics in the Southern Patagonian Andes. Field observations, based on geological, structural and geomorphic mapping, are combined with bedrock apatite (U-Th)/He and apatite fission track (AHe and AFT) cooling ages sampled along elevation transects across the orogen. This new data reveals the existence of hitherto unrecognized neotectonic deformation along the flanks of the range capped by the NPI.
This deformation is associated with the closely spaced oblique collision of successive oceanic-ridge segments in this region over the past 6 Ma. I interpret that this has caused a crustal-scale partitioning of deformation and the decoupling, margin-parallel migration, and localized uplift of a large crustal sliver (the NPI block) along the subduction margin. The location of this uplift coincides with a major increase of summit elevations and relief at the northern edge of the NPI massif. This mechanism is compatible with possible extensional processes along the topographically subdued trailing edge of the NPI block as documented by very recent and possibly still active normal faulting. Taken together, these findings suggest a major structural control on short-wavelength variations in topography in the Southern Patagonian Andes - the region affected by ridge collision and slab window formation.
The second research topic addressed here focuses on using my new and existing bedrock low-temperature cooling ages in forward and inverse thermal modeling. The data was implemented in the HeFTy and QTQt modeling platforms to constrain the late Cenozoic thermal history of the Southern Patagonian Andes in the region of the most recent upper-plate sectors of ridge collision. The data set combines AHe and AFT data from three elevation transects in the region of the Northern Patagonian Icefield. Previous similar studies claimed far-reaching thermal effects of the approaching ridge collision and slab window to affect patterns of Late Miocene reheating in the modelled thermal histories. In contrast, my results show that the currently available data can be explained with a simpler thermal history than previously proposed. Accordingly, a reheating event is not needed to reproduce the observations. Instead, the analyzed ensemble of modelled thermal histories defines a Late Miocene protracted cooling and Pliocene-to-recent stepwise exhumation. These findings agree with the geological record of this region. Specifically, this record indicates an Early Miocene phase of active mountain building associated with surface uplift and an active fold-and-thrust belt, followed by a period of stagnating deformation, peneplanation, and lack of synorogenic deposition in the Patagonian foreland. The subsequent period of stepwise exhumation likely resulted from a combination of pulsed glacial erosion and coeval neotectonic activity. The differences between the present and previously published interpretation of the cooling record can be reconciled with important inconsistencies of previously used model setup. These include mainly the insufficient convergence of the models and improper assumptions regarding the geothermal conditions in the region. This analysis puts a methodological emphasis on the prime importance of the model setup and the need for its thorough examination to evaluate the robustness of the final outcome.
This study presents noble gas compositions (He, Ne, Ar, Kr, and Xe) of lavas from several Hawaiian volcanoes. Lavas from the Hawaii Scientific Drilling Project (HSDP) core, surface samples from Mauna Kea, Mauna Loa, Kilauea, Hualalai, Kohala and Haleakala as well as lavas from a deep well on the summit of Kilauea were investigated. Noble gases, especially helium, are used as tracers for mantle reservoirs, based on the assumption that high 3He/4He ratios (>8 RA) represent material from the deep and supposedly less degassed mantle, whereas lower ratios (~ 8 RA) are thought to represent the upper mantle. Shield stage Mauna Kea, Kohala and Kilauea lavas yielded MORB-like to moderately high 3He/4He ratios, while 3He/4He ratios in post-shield stage Haleakala lavas are MORB-like. Few samples show 20Ne/22Ne and 21Ne/22Ne ratios different from the atmospheric values, however, Mauna Kea and Kilauea lavas with excess in mantle Ne agree well with the Loihi-Kilauea line in a neon three-isotope plot, whereas one Kohala sample plots on the MORB correlation line. The values in the 4He/40Ar* (40Ar* denotes radiogenic Ar) versus 4He diagram imply open system fractionation of He from Ar, with a deficiency in 4He. Calculated 4He/40Ar*, 3He/22Nes (22NeS denotes solar Ne) and 4He/21Ne ratios for the sample suite are lower than the respective production and primordial ratios, supporting the observation of a fractionation of He from the heavier noble gases, with a depletion of He with respect to Ne and Ar. The depletion of He is interpreted to be partly due to solubility controlled gas loss during magma ascent. However, the preferential He loss suggests that He is more incompatible than Ne and Ar during magmatic processes. In a binary mixing model, the isotopic He and Ne pattern are best explained by a mixture of a MORB-like end-member with a plume like or primordial end-member with a fractionation in 3He/22Ne, represented by a curve parameter r of 15 (r=(³He/²²Ne)MORB/(³He/²²Ne)PLUME or PRIMORDIAL). Whether the high 3He/4He ratios in Hawaiian lavas are indicative of a primitive component within the Hawaiian plume or are rather a product of the crystal-melt- partitioning behavior during partial melting remains to be resolved.
The Andean orogen is the most outstanding example of mountain building caused by the subduction of oceanic below continental lithosphere. The Andes formed by the subduction of the Nazca and Antarctic oceanic plates under the South American continent over at least ~200 million years. Tectonic and climatic conditions vary markedly along this north-south–oriented plate boundary, which thus represents an ideal natural laboratory to study tectonic and climatic segmentation processes and their possible feedbacks. Most of the seismic energy on Earth is released by earthquakes in subduction zones, like the giant 1960, Mw 9.5 event in south-central Chile. However, the segmentation mechanisms of surface deformation during and between these giant events have remained poorly understood. The Andean margin is a key area to study seismotectonic processes because of its along-strike variability under similar plate kinematic boundary conditions. Active deformation has been widely studied in the central part of the Andes, but the south-central sector of the orogen has gathered less research efforts. This study focuses on tectonics at the Neogene and late Quaternary time scales in the Main Cordillera and coastal forearc of the south-central Andes. For both domains I document the existence of previously unrecognized active faults and present estimates of deformation rates and fault kinematics. Furthermore these data are correlated to address fundamental mountain building processes like strain partitioning and large-scale segmentation. In the Main Cordillera domain and at the Neogene timescale, I integrate structural and stratigraphic field observations with published isotopic ages to propose four main phases of coupled styles of tectonics and distribution of volcanism and magmatism. These phases can be related to the geometry and kinematics of plate convergence. At the late Pleistocene timescale, I integrate field observations with lake seismic and bathymetric profiles from the Lago Laja region, located near the Andean drainage divide. These data reveal Holocene extensional faults, which define the Lago Laja fault system. This fault system has no significant strike-slip component, contrasting with the Liquiñe-Ofqui dextral intra-arc system to the south, where Holocene strike-slip markers are ubiquitous. This contrast in structural style along the arc is coincident with a marked change in along-strike fault geometries in the forearc, across the Arauco Peninsula. Thereon I propose that a net gradient in the degree of partitioning of oblique subduction occurs across the Arauco transition zone. To the north, the margin parallel component of oblique convergence is distributed in a wide zone of diffuse deformation, while to the south it is partitioned along an intra-arc, margin-parallel strike-slip fault zone. In the coastal forearc domain and at the Neogene timescale, I integrate structural and stratigraphic data from field observations, industry reflection-seismic profiles and boreholes to emphasize the influence of climate-driven filling of the trench on the mechanics and kinematics of the margin. I show that forearc basins in the 34-45°S segment record Eocene to early Pliocene extension and subsidence followed by ongoing uplift and contraction since the late Pliocene. I interpret the first stage as caused by tectonic erosion due to high plate convergence rates and reduced trench fill. The subsequent stage, in turn, is related to accretion caused by low convergence rates and the rapid increase in trench fill after the onset of Patagonian glaciations and climate-driven exhumation at ~6-5 Ma. On the late Quaternary timescale, I integrate off-shore seismic profiles with the distribution of deformed marine terraces from Isla Santa María, dated by the radiocarbon method, to show that inverted reverse faulting controls the coastal geomorphology and segmentation of surface deformation. There, a cluster of microearthquakes illuminates one of these reverse faults, which presumingly reaches the plate interface. Furthermore, I use accounts of coseismic uplift during the 1835 M>8 earthquake made by Charles Darwin, to propose that this active reverse fault has been mechanically coupled to the megathrust. This has important implications on the assessment of seismic hazards in this, and other similar regions. These results underscore the need to study plate-boundary deformation processes at various temporal and spatial scales and to integrate geomorphologic, structural, stratigraphic, and geophysical data sets in order to understand the present distribution and causes of tectonic segmentation.
Permafrost is warming globally, which leads to widespread permafrost thaw and impacts the surrounding landscapes, ecosystems and infrastructure. Especially ice-rich permafrost is vulnerable to rapid and abrupt thaw, resulting from the melting of excess ground ice. Local remote sensing studies have detected increasing rates of abrupt permafrost disturbances, such as thermokarst lake change and drainage, coastal erosion and RTS in the last two decades. All of which indicate an acceleration of permafrost degradation.
In particular retrogressive thaw slumps (RTS) are abrupt disturbances that expand by up to several meters each year and impact local and regional topographic gradients, hydrological pathways, sediment and nutrient mobilisation into aquatic systems, and increased permafrost carbon mobilisation. The feedback between abrupt permafrost thaw and the carbon cycle is a crucial component of the Earth system and a relevant driver in global climate models. However, an assessment of RTS at high temporal resolution to determine the dynamic thaw processes and identify the main thaw drivers as well as a continental-scale assessment across diverse permafrost regions are still lacking.
In northern high latitudes optical remote sensing is restricted by environmental factors and frequent cloud coverage. This decreases image availability and thus constrains the application of automated algorithms for time series disturbance detection for large-scale abrupt permafrost disturbances at high temporal resolution. Since models and observations suggest that abrupt permafrost disturbances will intensify, we require disturbance products at continental-scale, which allow for meaningful integration into Earth system models.
The main aim of this dissertation therefore, is to enhance our knowledge on the spatial extent and temporal dynamics of abrupt permafrost disturbances in a large-scale assessment. To address this, three research objectives were posed:
1. Assess the comparability and compatibility of Landsat-8 and Sentinel-2 data for a combined use in multi-spectral analysis in northern high latitudes.
2. Adapt an image mosaicking method for Landsat and Sentinel-2 data to create combined mosaics of high quality as input for high temporal disturbance assessments in northern high latitudes.
3. Automatically map retrogressive thaw slumps on the landscape-scale and assess their high temporal thaw dynamics.
We assessed the comparability of Landsat-8 and Sentinel-2 imagery by spectral comparison of corresponding bands. Based on overlapping same-day acquisitions of Landsat-8 and Sentinel-2 we derived spectral bandpass adjustment coefficients for North Siberia to adjust Sentinel-2 reflectance values to resemble Landsat-8 and harmonise the two data sets. Furthermore, we adapted a workflow to combine Landsat and Sentinel-2 images to create homogeneous and gap-free annual mosaics. We determined the number of images and cloud-free pixels, the spatial coverage and the quality of the mosaic with spectral comparisons to demonstrate the relevance of the Landsat+Sentinel-2 mosaics. Lastly, we adapted the automatic disturbance detection algorithm LandTrendr for large-scale RTS identification and mapping at high temporal resolution. For this, we modified the temporal segmentation algorithm for annual gradual and abrupt disturbance detection to incorporate the annual Landsat+Sentinel-2 mosaics. We further parametrised the temporal segmentation and spectral filtering for optimised RTS detection, conducted further spatial masking and filtering, and implemented a binary object classification algorithm with machine-learning to derive RTS from the LandTrendr disturbance output. We applied the algorithm to North Siberia, covering an area of 8.1 x 106 km2.
The spectral band comparison between same-day Landsat-8 and Sentinel-2 acquisitions already showed an overall good fit between both satellite products. However, applying the acquired spectral bandpass coefficients for adjustment of Sentinel-2 reflectance values, resulted in a near-perfect alignment between the same-day images. It can therefore be concluded that the spectral band adjustment succeeds in adjusting Sentinel-2 spectral values to those of Landsat-8 in North Siberia.
The number of available cloud-free images increased steadily between 1999 and 2019, especially intensified after 2016 with the addition of Sentinel-2 images. This signifies a highly improved input database for the mosaicking workflow. In a comparison of annual mosaics, the Landsat+Sentinel-2 mosaics always fully covered the study areas, while Landsat-only mosaics contained data-gaps for the same years. The spectral comparison of input images and Landsat+Sentinel-2 mosaic showed a high correlation between the input images and the mosaic bands, testifying mosaicking results of high quality. Our results show that especially the mosaic coverage for northern, coastal areas was substantially improved with the Landsat+Sentinel-2 mosaics. By combining data from both Landsat and Sentinel-2 sensors we reliably created input mosaics at high spatial resolution for comprehensive time series analyses.
This research presents the first automatically derived assessment of RTS distribution and temporal dynamics at continental-scale. In total, we identified 50,895 RTS, primarily located in ice-rich permafrost regions, as well as a steady increase in RTS-affected areas between 2001 and 2019 across North Siberia. From 2016 onward the RTS area increased more abruptly, indicating heightened thaw slump dynamics in this period. Overall, the RTS-affected area increased by 331 % within the observation period. Contrary to this, five focus sites show spatiotemporal variability in their annual RTS dynamics, alternating between periods of increased and decreased RTS development. This suggests a close relationship to varying thaw drivers. The majority of identified RTS was active from 2000 onward and only a small proportion initiated during the assessment period. This highlights that the increase in RTS-affected area was mainly caused by enlarging existing RTS and not by newly initiated RTS.
Overall, this research showed the advantages of combining Landsat and Sentinel-2 data in northern high latitudes and the improvements in spatial and temporal coverage of combined annual mosaics. The mosaics build the database for automated disturbance detection to reliably map RTS and other abrupt permafrost disturbances at continental-scale. The assessment at high temporal resolution further testifies the increasing impact of abrupt permafrost disturbances and likewise emphasises the spatio-temporal variability of thaw dynamics across landscapes. Obtaining such consistent disturbance products is necessary to parametrise regional and global climate change models, for enabling an improved representation of the permafrost thaw feedback.
Two of the most controversial issues concerning the late Cenozoic evolution of the Andean orogen are the timing of uplift of the intraorogenic Puna plateau and its eastern border, the Eastern Cordillera, and ensuing changes in climatic and surface-process conditions in the intermontane basins of the NW-Argentine Andes. The Eastern Cordillera separates the internally drained, arid Puna from semi-arid intermontane basins and the humid sectors of the Andean broken foreland and the Subandean fold-and-thrust belt to the east. With elevations between 4,000 and 6,000 m the eastern flanks of the Andes form an efficient orographic barrier with westward-increasing elevation and asymmetric rainfall distribution and amount with respect to easterly moisture-bearing winds. This is mirrored by pronounced gradients in the efficiency of surface processes that erode and re-distribute sediment from the uplifting ranges. Although the overall pattern of deformation and uplift in this sector of the southern central Andes shows an eastward migration of deformation, a well-developed deformation front does not exist and uplift and associated erosion and sedimentary processes are highly disparate in space and time. In addition, periodic deformation within intermontane basins, and continued diachronous foreland uplifts associated with the reactivation of inherited basement structures furthermore make a rigorous assessment of the spatiotemporal uplift patterns difficult.
This thesis focuses on the tectonic evolution of the Eastern Cordillera of NW Argentina, the depositional history of its intermontane sedimentary basins, and the regional topographic evolution of the eastern flank of the Puna Plateau. The intermontane basins of the Eastern Cordillera and the adjacent morphotectonic provinces of the Sierras Pampeanas and the Santa Bárbara System are akin to reverse fault bounded, filled, and partly coalesced sedimentary basins of the Puna Plateau. In contrast to the Puna basins, however, which still form intact morphologic entities, repeated deformation, erosion, and re-filling have impacted the basins in the Eastern Cordillera. This has resulted in a rich stratigraphy of repeated basin fills, but many of these basins have retained vestiges of their early depositional history that may reach back in time when these areas were still part of a contiguous and undeformed foreland basin. Fortunately, these strata also contain abundant volcanic ashes that are not only important horizons to decipher tectono-sedimentary events through U-Pb geochronology and geochemical correlation, but they also represent terrestrial recorders of the hydrogen-isotope composition of ancient meteoric waters that can be compared to the isotopic composition of modern meteoric water. The ash horizons are thus unique recorders of past environmental conditions and lend themselves to tracking the development of rainfall barriers and tectonically forced climate and environmental change through time.
U-Pb zircon geochronology and paleocurrent reconstructions of conglomerate sequences in the Humahuaca Basin of the Eastern Cordillera at 23.5° S suggest that the basin was an integral part of a largely unrestricted depositional system until 4.2 Ma, which subsequently became progressively decoupled from the foreland by range uplifts to the east that forced easterly moisture-bearing winds to precipitate in increasingly eastward locations. Multiple cycles of severed hydrological conditions and drainage re-capture are identified together with these processes that were associated with basin filling and sediment evacuation, respectively. Moreover, systematic relationships among faults, regional unconformities and deformed landforms reveal a general pattern of intra-basin deformation that appears to be linked with basin-internal deformation during or subsequent to episodes of large-scale sediment removal. Some of these observations are supported by variations in the hydrogen stable isotope composition of volcanic glass from the Neogene to Quaternary sedimentary record, which can be related to spatiotemporal changes in topography and associated orographic effects. δDg values in the basin strata reveal two main trends associated with surface uplift in the catchment area between 6.0 and 3.5 Ma and the onset of semiarid conditions in the basin following the attainment of threshold elevations for effective orographic barriers to the east after 3.5 Ma. The disruption of sediment supply from western sources after 4.2 Ma and subsequent hinterland aridification, moreover, emphasize the possibility that these processes were related to lateral orogenic growth of the adjacent Puna Plateau. As a result of the hinterland aridification the regions in the orogen interior have been characterized by an inefficient fluvial system, which in turn has helped maintaining internal drainage conditions, sediment storage, and relief reduction within high-elevation basins.
The diachronous nature of basin formation and impacts on the fluvial system in the adjacent broken foreland is underscored by the results of detailed sediment provenance and paleocurrent analyses, as well as U-Pb zircon geochronology in the Lerma and Metán basins at ca. 25° S. This is particularly demonstrated by the isolated uplift of the Metán range at ~10 Ma, which is more than 50 km away from the presently active orogenic front along the eastern Puna margin and the Eastern Cordillera to the west. At about 5 Ma, Puna-sourced sediments disappear from the foreland record, documenting further range uplifts in the Eastern Cordillera and hydrological isolation of the neighboring Angastaco Basin from the foreland. Finally, during the late Pliocene and Quaternary, deformation has been accommodated across the entire foreland and is still active. To elucidate the interactions between tectonically controlled changes in elevation and their impact on atmospheric circulation processes in this region, this thesis provides additional, temporally well-constrained hydrogen stable isotope results of volcanic glass samples from the broken foreland, including the Angastaco Basin, and other intermontane basins farther south. The results suggest similar elevations of intermontane basins and the foreland sectors prior to ca. 7 Ma. In case of the Angastaco Basin the region was affected by km-scale surface uplift of the basin. A comparison with coeval isotope data collected from sedimentary sequences in the Puna plateau explains rapid shifts in the intermontane δDg record and supports the notion of recurring phases of enhanced deep convection during the Pliocene, and thus climatic conditions during the middle to late Pliocene similar to the present day.
Combined, field-based and isotope geochemical methods used in this study of the NW-Argentine Andes have thus helped to gain insight into the systematics, rate changes, interactions, and temporal characteristics among tectonically controlled deformation patterns, the build-up of topography impacting atmospheric processes, the distribution of rainfall, and resulting surface processes in a tectonically active mountain belt. Ultimately, this information is essential for a better understanding of the style and the rates at which non-collisional mountain belts evolve, including the development orogenic plateaus and their bordering flanks. The results presented in this study emphasize the importance of stable isotope records for paleoaltimetric and paleoenvironmental studies in mountain belts and furnishes important data for a rigorous interpretation of such records.
Lava domes are severely hazardous, mound-shaped extrusions of highly viscous lava and commonly erupt at many active stratovolcanoes around the world. Due to gradual growth and flank oversteepening, such lava domes regularly experience partial or full collapses, resulting in destructive and far-reaching pyroclastic density currents. They are also associated with cyclic explosive activity as the complex interplay of cooling, degassing, and solidification of dome lavas regularly causes gas pressurizations on the dome or the underlying volcano conduit. Lava dome extrusions can last from days to decades, further highlighting the need for accurate and reliable monitoring data.
This thesis aims to improve our understanding of lava dome processes and to contribute to the monitoring and prediction of hazards posed by these domes. The recent rise and sophistication of photogrammetric techniques allows for the extraction of observational data in unprecedented detail and creates ideal tools for accomplishing this purpose. Here, I study natural lava dome extrusions as well as laboratory-based analogue models of lava dome extrusions and employ photogrammetric monitoring by Structure-from-Motion (SfM) and Particle-Image-Velocimetry (PIV) techniques. I primarily use aerial photography data obtained by helicopter, airplanes, Unoccupied Aircraft Systems (UAS) or ground-based timelapse cameras. Firstly, by combining a long time-series of overflight data at Volcán de Colima, México, with seismic and satellite radar data, I construct a detailed timeline of lava dome and crater evolution. Using numerical model, the impact of the extrusion on dome morphology and loading stress is further evaluated and an impact on the growth direction is identified, bearing important implications for the location of collapse hazards. Secondly, sequential overflight surveys at the Santiaguito lava dome, Guatemala, reveal surface motion data in high detail. I quantify the growth of the lava dome and the movement of a lava flow, showing complex motions that occur on different timescales and I provide insight into rock properties relevant for hazard assessment inferred purely by photogrammetric processing of remote sensing data. Lastly, I recreate artificial lava dome and spine growth using analogue modelling under controlled conditions, providing new insights into lava extrusion processes and structures as well as the conditions in which they form.
These findings demonstrate the capabilities of photogrammetric data analyses to successfully monitor lava dome growth and evolution while highlighting the advantages of complementary modelling methods to explain the observed phenomena. The results presented herein further bear important new insights and implications for the hazards posed by lava domes.
This study presents the development of 1D and 2D Surface Evolution Codes (SECs) and their coupling to any lithospheric-scale (thermo-)mechanical code with a quadrilateral structured surface mesh.
Both SECs involve diffusion as approach for hillslope processes and the stream power law to reflect riverbed incision. The 1D SEC settles sediment that was produced by fluvial incision in the appropriate minimum, while the supply-limited 2D SEC DANSER uses a fast filling algorithm to model sedimantation. It is based on a cellular automaton. A slope-dependent factor in the sediment flux extends the diffusion equation to nonlinear diffusion. The discharge accumulation is achieved with the D8-algorithm and an improved drainage accumulation routine. Lateral incision enhances the incision's modelling. Following empirical laws, it incises channels of several cells width.
The coupling method enables different temporal and spatial resolutions of the SEC and the thermo-mechanical code. It transfers vertical as well as horizontal displacements to the surface model. A weighted smoothing of the 3D surface displacements is implemented. The smoothed displacement vectors transmit the deformation by bilinear interpolation to the surface model. These interpolation methods ensure mass conservation in both directions and prevent the two surfaces from drifting apart.
The presented applications refer to the evolution of the Pamir orogen. A calibration of DANSER's parameters with geomorphological data and a DEM as initial topography highlights the advantage of lateral incision. Preserving the channel width and reflecting incision peaks in narrow channels, this closes the huge gap between current orogen-scale incision models and observed topographies.
River capturing models in a system of fault-bounded block rotations reaffirm the importance of the lateral incision routine for capturing events with channel initiation. The models show a low probability of river capturings with large deflection angles. While the probability of river capturing is directly depending on the uplift rate, the erodibility inside of a dip-slip fault speeds up headward erosion along the fault: The model's capturing speed increases within a fault.
Coupling DANSER with the thermo-mechanical code SLIM 3D emphasizes the versatility of the SEC. While DANSER has minor influence on the lithospheric evolution of an indenter model, the brittle surface deformation is strongly affected by its sedimentation, widening a basin in between two forming orogens and also the southern part of the southern orogen to south, east and west.
Modelling of environmental change impacts on water resources and hydrological extremes in Germany
(2012)
Water resources, in terms of quantity and quality, are significantly influenced by environmental changes, especially by climate and land use changes. The main objective of the present study is to project climate change impacts on the seasonal dynamics of water fluxes, spatial changes in water balance components as well as the future flood and low flow conditions in Germany. This study is based on the modeling results of the process-based eco-hydrological model SWIM (Soil and Water Integrated Model) driven by various regional climate scenarios on one hand. On the other hand, it is supported by statistical analysis on long-term trends of observed and simulated time series. In addition, this study evaluates the impacts of potential land use changes on water quality in terms of NO3-N load in selected sub-regions of the Elbe basin. In the context of climate change, the actual evapotransipration is likely to increase in most parts of Germany, while total runoff generation may decrease in south and east regions in the scenario period 2051-2060. Water discharge in all six studied large rivers (Ems, Weser, Saale, Danube, Main and Neckar) would be 8 – 30% lower in summer and autumn compared to the reference period (1961 – 1990), and the strongest decline is expected for the Saale, Danube and Neckar. The 50-year low flow is likely to occur more frequently in western, southern and central Germany after 2061 as suggested by more than 80% of the model runs. The current low flow period (from August to September) may be extended until the late autumn at the end of this century. Higher winter flow is expected in all of these rivers, and the increase is most significant for the Ems (about 18%). No general pattern of changes in flood directions can be concluded according to the results driven by different RCMs, emission scenarios and multi-realizations. An optimal agricultural land use and management are essential for the reduction in nutrient loads and improvement of water quality. In the Weiße Elster and Unstrut sub-basins (Elbe), an increase of 10% in the winter rape area can result in 12-19% more NO3-N load in rivers. In contrast, another energy plant, maize, has a moderate effect on the water environment. Mineral fertilizers have a much stronger effect on the NO3-N load than organic fertilizers. Cover crops, which play an important role in the reduction of nitrate losses from fields, should be maintained on cropland. The uncertainty in estimating future high flows and, in particular, extreme floods remain high due to different RCM structures, emission scenarios and multi-realizations. In contrast, the projection of low flows under warmer climate conditions appears to be more pronounced and consistent. The largest source of uncertainty related to NO3-N modelling originates from the input data on the agricultural management.
In den letzten drei Jahrzehnten wurden in einigen Seen und Feuchtgebieten in bewaldeten Einzugsgebieten Nordost-Brandenburgs sinkende Wasserstände beobachtet. In diesen Gebieten bestimmt die Grundwasserneubildung im Einzugsgebiet maßgeblich das Wasserdargebot der Seen und Feuchtgebiete, die deshalb hier als grundwasserabhängige Landschaftselemente bezeichnet werden. Somit weisen die sinkenden Wasserstände auf einen Rückgang der wegen des geringen Niederschlagsdargebotes ohnehin schon geringen Grundwasserneubildung hin. Die Höhe der Grundwasserneubildung ist neben den hydroklimatischen Randbedingungen auch von der Landnutzung abhängig. Veränderungen in der Waldvegetation und der hydroklimatischen Randbedingungen bewirken Änderungen der Grundwasserneubildung und beeinflussen somit auch den Wasserhaushalt der Seen und Feuchtgebiete. Aktuell wird die Waldvegetation durch Kiefernmonokulturen dominiert, mit im Vergleich zu anderen Baumarten höherer Evapotranspiration. Entwicklungen in der Forstwirtschaft streben die Verringerung von Kiefernmonokulturen an. Diese sollen langfristig auf geeigneten Standorten durch Laubmischwälder ersetzt werden. Dadurch lassen sich eine geringere Evapotranspiration und damit eine höhere Grundwasserneubildung erreichen. In der vorliegenden Arbeit werden am Beispiel des Redernswalder Sees und des Briesensees die Ursachen der beobachteten sinkenden Wasserstände analysiert. Ihre Wasserstände nahmen in den letzten 25 Jahren um mehr als 3 Meter ab. Weiterhin wird untersucht, wie die erwarteten Klimaänderungen und Veränderungen in der Waldbewirtschaftung die zukünftige Grundwasserneubildung und den Wasserhaushalt von Seen beeinflussen können. Die Entwicklung der Grundwasserneubildung im Untersuchungsgebiet wurde mit dem Wasserhaushaltsmodell WaSiM-ETH simuliert. Die Analyse der Wechselwirkungen der Seen mit dem regionalen quartären Grundwasserleitersystem erfolgte mit dem 3D-Grundwassermodell FEFLOW. Mögliche zukünftige Veränderungen der Grundwasserneubildung und der Seewasserstände durch Klimaänderungen und Waldumbau wurden mit Szenarienrechnungen bis zum Jahr 2100 analysiert. Die modellgestützte Analyse zeigte, dass die beobachteten abnehmenden Wasserstände zu etwa gleichen Anteilen durch Veränderungen der hydroklimatischen Randbedingungen sowie durch Veränderungen in der Waldvegetation und damit abnehmenden Grundwasserneubildungsraten zu erklären sind. Die zukünftigen Entwicklungen der Grundwasserneubildung und der Wasserstände sind geprägt von sich ändernden hydroklimatischen Randbedingungen und einem sukzessiven Wandel der Kiefernbestände zu Laubwäldern. Der Waldumbau hat positive Wirkungen auf die Grundwasserneubildung und damit auf die Wasserstände. Damit können die Einflüsse des eingesetzten REMO-A1B-Klimaszenarios zum Ende des Modellzeitraumes durch den Waldumbau nicht kompensiert werden, das Sinken des Wasserstandes wird jedoch wesentlich reduziert. Bei dem moderateren REMO-B1-Klimaszenario werden die Wasserstände des Jahres 2008 durch den Waldumbau bis zum Jahr 2100 überschritten.
Volcanic hazard assessment relies on physics-based models of hazards, such as lava flows and pyroclastic density currents, whose outcomes are very sensitive to the location where future eruptions will occur. On the contrary, forecast of vent opening locations in volcanic areas typically relies on purely data-driven approaches, where the spatial density of past eruptive vents informs the probability maps of future vent opening. Such techniques may be suboptimal in volcanic systems with missing or scarce data, and where the controls on magma pathways may change over time. An alternative approach was recently proposed, relying on a model of stress-driven pathways of magmatic dikes. In that approach, the crustal stress was optimized so that dike trajectories linked consistently the location of the magma chamber to that of past vents. The retrieved information on the stress state was then used to forecast future dike trajectories. The validation of such an approach requires extensive application to nature. Before doing so, however, several important limitations need to be removed, most importantly the two-dimensional (2D) character of the models and theoretical concepts. In this thesis, I develop methods and tools so that a physics-based strategy of stress inversion and eruptive vent forecast in volcanoes can be applied to three dimensional (3D) problems. In the first part, I test the stress inversion and vent forecast strategy on analog models, still within a 2D framework, but improving on the efficiency of the stress optimization. In the second part, I discuss how to correctly account for gravitational loading/unloading due to complex 3D topography with a Boundary-Element numerical model. Then, I develop a new, simplified but fast model of dike pathways in 3D, designed for running large numbers of simulations at minimal computational cost, and able to backtrack dike trajectories from vents on the surface. Finally, I combine the stress and dike models to simulate dike pathways in synthetic calderas. In the third part, I describe a framework of stress inversion and vent forecast strategy in 3D for calderas. The stress inversion relies on, first, describing the magma storage below a caldera in terms of a probability density function. Next, dike trajectories are backtracked from the known locations of past vents down through the crust, and the optimization algorithm seeks for the stress models which lead trajectories through the regions of highest probability. I apply the new strategy to the synthetic scenarios presented in the second part, and I exploit the results from the stress inversions to produce probability maps of future vent locations for some of those scenarios. In the fourth part, I present the inversion of different deformation source models applied to the ongoing ground deformation observed across the Rhenish Massif in Central Europe. The region includes the Eifel Volcanic Fields in Germany, a potential application case for the vent forecast strategy. The results show how the observed deformation may be due to melt accumulation in sub-horizontal structures in the lower crust or upper mantle. The thesis concludes with a discussion of the stress inversion and vent forecast strategy, its limitations and applicability to real volcanoes. Potential developments of the modeling tools and concepts presented here are also discussed, as well as possible applications to other geophysical problems.
The timing and location of the two largest earthquakes of the 21st century (Sumatra, 2004 and Tohoku 2011, events) greatly surprised the scientific community, indicating that the deformation processes that precede and follow great megathrust earthquakes remain enigmatic. During these phases before and after the earthquake a combination of multi-scale complex processes are acting simultaneously: Stresses built up by long-term tectonic motions are modified by sudden jerky deformations during earthquakes, before being restored by multiple ensuing relaxation processes.
This thesis details a cross-scale thermomechanical model developed with the aim of simulating the entire subduction process from earthquake (1 minute) to million years’ time scale, excluding only rupture propagation. The model employs elasticity, non-linear transient viscous rheology, and rate-and-state friction. It generates spontaneous earthquake sequences, and, by using an adaptive time-step algorithm, recreates the deformation process as observed naturally over single and multiple seismic cycles. The model is thoroughly tested by comparing results to those from known high- resolution solutions of generic modeling setups widely used in modeling of rupture propagation. It is demonstrated, that while not modeling rupture propagation explicitly, the modeling procedure correctly recognizes the appearance of instability (earthquake) and correctly simulates the cumulative slip at a fault during great earthquake by means of a quasi-dynamic approximation.
A set of 2D models is used to study the effects of non-linear transient rheology on the postseismic processes following great earthquakes. Our models predict that the viscosity in the mantle wedge drops by 3 to 4 orders of magnitude during a great earthquake with magnitude above 9. This drop in viscosity results in spatial scales and timings of the relaxation processes following the earthquakes that are significantly different to previous estimates. These models replicate centuries long seismic cycles exhibited by the greatest earthquakes (like the Great Chile 1960 Earthquake) and are consistent with the major features of postseismic surface displacements recorded after the Great Tohoku Earthquake.
The 2D models are also applied to study key factors controlling maximum magnitudes of earthquakes in subduction zones. Even though methods of instrumentally observing earthquakes at subduction zones have rapidly improved in recent decades, the characteristic recurrence interval of giant earthquakes (Mw>8.5) is much larger than the currently available observational record and therefore the necessary conditions for giant earthquakes are not clear. Statistical studies have recognized the importance of the slab shape and its surface roughness, state of the strain of the upper plate and thickness of sediments filling the trenches. In this thesis we attempt to explain these observations and to identify key controlling parameters. We test a set of 2D models representing great earthquake seismic cycles at known subduction zones with various known geometries, megathrust friction coefficients, and convergence rates implemented. We found that low-angle subduction (large effect) and thick sediments in the subduction channel (smaller effect) are the fundamental necessary conditions for generating giant earthquakes, while the change of subduction velocity from 10 to 3.5 cm/yr has a lower effect. Modeling results also suggest that having thick sediments in the subduction channel causes low static friction, resulting in neutral or slightly compressive deformation in the overriding plate for low-angle subduction zones. These modeling results agree well with observations for the largest earthquakes. The model predicts the largest possible earthquakes for subduction zones of given dipping angles. The predicted maximum magnitudes exactly threshold magnitudes of all known giant earthquakes of 20th and 21st centuries.
The clear limitation of most of the models developed in the thesis is their 2D nature. Development of 3D models with comparable resolution and complexity will require significant advances in numerical techniques. Nevertheless, we conducted a series of low-resolution 3D models to study the interaction between two large asperities at a subduction interface separated by an aseismic gap of varying width. The novelty of the model is that it considers behavior of the asperities during multiple seismic cycles. As expected, models show that an aseismic gap with a narrow width could not prevent rupture propagation from one asperity to another, and that rupture always crosses the entire model. When the gap becomes too wide, asperities do not interact anymore and rupture independently. However, an interesting mode of interaction was observed in the model with an intermediate width of the aseismic gap: In this model the asperities began to stably rupture in anti-phase following multiple seismic cycles. These 3D modeling results, while insightful, must be considered preliminary because of the limitations in resolution.
The technique developed in this thesis for cross-scale modeling of seismic cycles can be used to study the effects of multiple seismic cycles on the long-term deformation of the upper plate. The technique can be also extended to the case of continental transform faults and for the advanced 3D modeling of specific subduction zones. This will require further development of numerical techniques and adaptation of the existing advanced highly scalable parallel codes like LAMEM and ASPECT.
Extreme flooding displaces an average of 12 million people every year. Marginalized populations in low-income countries are in particular at high risk, but also industrialized countries are susceptible to displacement and its inherent societal impacts. The risk of being displaced results from a complex interaction of flood hazard, population exposed in the floodplains, and socio-economic vulnerability. Ongoing global warming changes the intensity, frequency, and duration of flood hazards, undermining existing protection measures. Meanwhile, settlements in attractive yet hazardous flood-prone areas have led to a higher degree of population exposure. Finally, the vulnerability to displacement is altered by demographic and social change, shifting economic power, urbanization, and technological development. These risk components have been investigated intensively in the context of loss of life and economic damage, however, only little is known about the risk of displacement under global change.
This thesis aims to improve our understanding of flood-induced displacement risk under global climate change and socio-economic change. This objective is tackled by addressing the following three research questions. First, by focusing on the choice of input data, how well can a global flood modeling chain reproduce flood hazards of historic events that lead to displacement? Second, what are the socio-economic characteristics that shape the vulnerability to displacement? Finally, to what degree has climate change potentially contributed to recent flood-induced displacement events?
To answer the first question, a global flood modeling chain is evaluated by comparing simulated flood extent with satellite-derived inundation information for eight major flood events. A focus is set on the sensitivity to different combinations of the underlying climate reanalysis datasets and global hydrological models which serve as an input for the global hydraulic model. An evaluation scheme of performance scores shows that simulated flood extent is mostly overestimated without the consideration of flood protection and only for a few events dependent on the choice of global hydrological models. Results are more sensitive to the underlying climate forcing, with two datasets differing substantially from a third one. In contrast, the incorporation of flood protection standards results in an underestimation of flood extent, pointing to potential deficiencies in the protection level estimates or the flood frequency distribution within the modeling chain.
Following the analysis of a physical flood hazard model, the socio-economic drivers of vulnerability to displacement are investigated in the next step. For this purpose, a satellite- based, global collection of flood footprints is linked with two disaster inventories to match societal impacts with the corresponding flood hazard. For each event the number of affected population, assets, and critical infrastructure, as well as socio-economic indicators are computed. The resulting datasets are made publicly available and contain 335 displacement events and 695 mortality/damage events. Based on this new data product, event-specific displacement vulnerabilities are determined and multiple (national) dependencies with the socio-economic predictors are derived. The results suggest that economic prosperity only partially shapes vulnerability to displacement; urbanization, infant mortality rate, the share of elderly, population density and critical infrastructure exhibit a stronger functional relationship, suggesting that higher levels of development are generally associated with lower vulnerability.
Besides examining the contextual drivers of vulnerability, the role of climate change in the context of human displacement is also being explored. An impact attribution approach is applied on the example of Cyclone Idai and associated extreme coastal flooding in Mozambique. A combination of coastal flood modeling and satellite imagery is used to construct factual and counterfactual flood events. This storyline-type attribution method allows investigating the isolated or combined effects of sea level rise and the intensification of cyclone wind speeds on coastal flooding. The results suggest that displacement risk has increased by 3.1 to 3.5% due to the total effects of climate change on coastal flooding, with the effects of increasing wind speed being the dominant factor.
In conclusion, this thesis highlights the potentials and challenges of modeling flood- induced displacement risk. While this work explores the sensitivity of global flood modeling to the choice of input data, new questions arise on how to effectively improve the reproduction of flood return periods and the representation of protection levels. It is also demonstrated that disentangling displacement vulnerabilities is feasible, with the results providing useful information for risk assessments, effective humanitarian aid, and disaster relief. The impact attribution study is a first step in assessing the effects of global warming on displacement risk, leading to new research challenges, e.g., coupling fluvial and coastal flood models or the attribution of other hazard types and displacement events. This thesis is one of the first to address flood-induced displacement risk from a global perspective. The findings motivate for further development of the global flood modeling chain to improve our understanding of displacement vulnerability and the effects of global warming.
This study investigated the slope carbonates of two Miocene carbonate systems: the Maltese Islands (in the Central Mediterranean) and the Marion Plateau (Northeastern Australia, drilled during ODP Leg 194). The aim of the study was to trace the impact of the Miocene cooling steps (events Mi1-Mi6) in these carbonate systems, especially the Mi3 event, which took place around 13.6 Ma and deeply impacted the marine oxygen isotope record. This event also profoundly impacted oceanographic and climatic patterns, eventually leading to the establishment of the modern ice-house world. In particular, East Antarctica became ice covered at that period. The rational behind the present study was to investigate the impact that this event had on shallow water systems in order to complement the deep-sea record and hence acquire a more global perspective on Miocene climate change. The Maltese Islands were investigated for trends in bulk-rock carbon and oxygen isotopes, as well as bulk-rock mineralogy, clay minerals analysis and organic geochemisty. Results showed that the mid Miocene cooling event deeply impacted sedimentation at that location by changing sedimentation from carbonate to clay-rich sediments. Moreover, it was discovered that each phase of Antarctic glaciation, not just the major mid Miocene event, resulted in higher terrigenous input on Malta. Mass accumulation rates revealed that this was linked to increased runoff during periods when Antarctica was glaciated, and thus that the carbonate sediments were “diluted” by clay-rich sediments. The model subsequently developed to explain this implies feedback from Antarctic glaciations creating cold, dense air masses that push the ITCZ Northward, thus increasing precipitation on the North African subcontinent. Increased precipitation (or stronger African monsoon) accelerated continental weathering and runoff, thus bringing more terrigenous sediment to the paleo-location of the slope sediments of Malta. Spectral analysis of carbonate content and organic matter geochemical analysis furthermore suggest that the clay-rich intervals are similar to sapropelic deposits. On the Marion Plateau, trends in oxygen and carbon isotopes were obtained by measuring Cibicidoides spp foraminifers. Moreover, carbonate content was reconstructed using a chemical method (coulometer). Results show that the mid Miocene cooling step profoundly affected this system: a major drop in accumulation rates of carbonates occurs precisely at 13.8 Ma, around the time of the East Antarctic ice sheet formation. Moreover, sedimentation changes occurred at that time, carbonate fragments coming from neritic environments becoming less abundant, planktonic foraminifer content increasing and quartz and reworked glauconite being deposited. Conversely, a surprising result is that the major N12-N14 sea-level fall occurring around 11.5 Ma did not impact the accumulation of carbonates on the slope. This was unexpected since carbonate platform are very sensitive to sea-level changes. The model developed to explain that mass accumulation rates of carbonates diminished around 13.6 Ma (Mi3 Event) instead of 11.5 Ma (N12-N14 event), suggests that oceanic currents were controlling slope carbonate deposition on the Marion Plateau prior to the mid-Miocene, and that the mid Miocene event considerably increase their strength, hence reducing the amount of carbonate being deposited on slope sites. Moreover, by combining results from deep-sea oxygen isotopes with sea-level estimates based on coastal onlaps made during Leg 194, we constrain the amplitude of the N12-N14 sea-level fall to 90 meters. When integrating isotopic results from this study, this amplitude is lowered to 70 meters. A general conclusion of this work is that the mid Miocene climatic shift did impact carbonate systems, at least at the two locations studied. However, the nature of this response was highly dependant on the regional settings, in particular the presence of land mass (Malta) and the absence of a barrier to shelter from the effects of open ocean (Marion Plateau).
Climate is the principal driving force of hydrological extremes like floods and attributing generating mechanisms is an essential prerequisite for understanding past, present, and future flood variability. Successively enhanced radiative forcing under global warming enhances atmospheric water-holding capacity and is expected to increase the likelihood of strong floods. In addition, natural climate variability affects the frequency and magnitude of these events on annual to millennial time-scales. Particularly in the mid-latitudes of the Northern Hemisphere, correlations between meteorological variables and hydrological indices suggest significant effects of changing climate boundary conditions on floods. To date, however, understanding of flood responses to changing climate boundary conditions is limited due to the scarcity of hydrological data in space and time. Exploring paleoclimate archives like annually laminated (varved) lake sediments allows to fill this gap in knowledge offering precise dated time-series of flood variability for millennia. During river floods, detrital catchment material is eroded and transported in suspension by fluid turbulence into downstream lakes. In the water body the transport capacity of the inflowing turbidity current successively diminishes leading to the deposition of detrital layers on the lake floor. Intercalated into annual laminations these detrital layers can be dated down to seasonal resolution. Microfacies analyses and X-ray fluorescence scanning (µ-XRF) at 200 µm resolution were conducted on the varved Mid- to Late Holocene interval of two sediment profiles from pre-alpine Lake Ammersee (southern Germany) located in a proximal (AS10prox) and distal (AS10dist) position towards the main tributary River Ammer. To shed light on sediment distribution within the lake, particular emphasis was (1) the detection of intercalated detrital layers and their micro-sedimentological features, and (2) intra-basin correlation of these deposits. Detrital layers were dated down to the season by microscopic varve counting and determination of the microstratigraphic position within a varve. The resulting chronology is verified by accelerator mass spectrometry (AMS) 14C dating of 14 terrestrial plant macrofossils. Since ~5500 varve years before present (vyr BP), in total 1573 detrital layers were detected in either one or both of the investigated sediment profiles. Based on their microfacies, geochemistry, and proximal-distal deposition pattern, detrital layers were interpreted as River Ammer flood deposits. Calibration of the flood layer record using instrumental daily River Ammer runoff data from AD 1926 to 1999 proves the flood layer succession to represent a significant time-series of major River Ammer floods in spring and summer, the flood season in the Ammersee region. Flood layer frequency trends are in agreement with decadal variations of the East Atlantic-Western Russia (EA-WR) atmospheric pattern back to 200 yr BP (end of the used atmospheric data) and solar activity back to 5500 vyr BP. Enhanced flood frequency corresponds to the negative EA-WR phase and reduced solar activity. These common links point to a central role of varying large-scale atmospheric circulation over Europe for flood frequency in the Ammersee region and suggest that these atmospheric variations, in turn, are likely modified by solar variability during the past 5500 years. Furthermore, the flood layer record indicates three shifts in mean layer thickness and frequency of different manifestation in both sediment profiles at ~5500, ~2800, and ~500 vyr BP. Combining information from both sediment profiles enabled to interpret these shifts in terms of stepwise increases in mean flood intensity. Likely triggers of these shifts are gradual reduction of Northern Hemisphere orbital summer forcing and long-term solar activity minima. Hypothesized atmospheric response to this forcing is hemispheric cooling that enhances equator-to-pole temperature gradients and potential energy in the troposphere. This energy is transferred into stronger westerly cyclones, more extreme precipitation, and intensified floods at Lake Ammersee. Interpretation of flood layer frequency and thickness data in combination with reanalysis models and time-series analysis allowed to reconstruct the flood history and to decipher flood triggering climate mechanisms in the Ammersee region throughout the past 5500 years. Flood frequency and intensity are not stationary, but influenced by multi-causal climate forcing of large-scale atmospheric modes on time-scales from years to millennia. These results challenge future projections that propose an increase in floods when Earth warms based only on the assumption of an enhanced hydrological cycle.
The Arctic is considered as a focal region in the ongoing climate change debate. The currently observed and predicted climate warming is particularly pronounced in the high northern latitudes. Rising temperatures in the Arctic cause progressive deepening and duration of permafrost thawing during the arctic summer, creating an ‘active layer’ with high bioavailability of nutrients and labile carbon for microbial consumption. The microbial mineralization of permafrost carbon creates large amounts of greenhouse gases, including carbon dioxide and methane, which can be released to the atmosphere, creating a positive feedback to global warming. However, to date, the microbial communities that drive the overall carbon cycle and specifically methane production in the Arctic are poorly constrained. To assess how these microbial communities will respond to the predicted climate changes, such as an increase in atmospheric and soil temperatures causing increased bioavailability of organic carbon, it is necessary to investigate the current status of this environment, but also how these microbial communities reacted to climate changes in the past. This PhD thesis investigated three records from two different study sites in the Russian Arctic, including permafrost, lake shore and lake deposits from Siberia and Chukotka. A combined stratigraphic approach of microbial and molecular organic geochemical techniques were used to identify and quantify characteristic microbial gene and lipid biomarkers. Based on this data it was possible to characterize and identify the climate response of microbial communities involved in past carbon cycling during the Middle Pleistocene and the Late Pleistocene to Holocene. It is shown that previous warmer periods were associated with an expansion of bacterial and archaeal communities throughout the Russian Arctic, similar to present day conditions. Different from this situation, past glacial and stadial periods experienced a substantial decrease in the abundance of Bacteria and Archaea. This trend can also be confirmed for the community of methanogenic archaea that were highly abundant and diverse during warm and particularly wet conditions. For the terrestrial permafrost, a direct effect of the temperature on the microbial communities is likely. In contrast, it is suggested that the temperature rise in scope of the glacial-interglacial climate variations led to an increase of the primary production in the Arctic lake setting, as can be seen in the corresponding biogenic silica distribution. The availability of this algae-derived carbon is suggested to be a driver for the observed pattern in the microbial abundance. This work demonstrates the effect of climate changes on the community composition of methanogenic archae. Methanosarcina-related species were abundant throughout the Russian Arctic and were able to adapt to changing environmental conditions. In contrast, members of Methanocellales and Methanomicrobiales were not able to adapt to past climate changes. This PhD thesis provides first evidence that past climatic warming led to an increased abundance of microbial communities in the Arctic, closely linked to the cycling of carbon and methane production. With the predicted climate warming, it may, therefore, be anticipated that extensive amounts of microbial communities will develop. Increasing temperatures in the Arctic will affect the temperature sensitive parts of the current microbiological communities, possibly leading to a suppression of cold adapted species and the prevalence of methanogenic archaea that tolerate or adapt to increasing temperatures. These changes in the composition of methanogenic archaea will likely increase the methane production potential of high latitude terrestrial regions, changing the Arctic from a carbon sink to a source.
Climatic variations and human activity now and increasingly in the future cause land cover changes and introduce perturbations in the terrestrial carbon reservoirs in vegetation, soil and detritus. Optical remote sensing and in particular Imaging Spectroscopy has shown the potential to quantify land surface parameters over large areas, which is accomplished by taking advantage of the characteristic interactions of incident radiation and the physico-chemical properties of a material. The objective of this thesis is to quantify key soil parameters, including soil organic carbon, using field and Imaging Spectroscopy. Organic carbon, iron oxides and clay content are selected to be analyzed to provide indicators for ecosystem function in relation to land degradation, and additionally to facilitate a quantification of carbon inventories in semiarid soils. The semiarid Albany Thicket Biome in the Eastern Cape Province of South Africa is chosen as study site. It provides a regional example for a semiarid ecosystem that currently undergoes land changes due to unadapted management practices and furthermore has to face climate change induced land changes in the future. The thesis is divided in three methodical steps. Based on reflectance spectra measured in the field and chemically determined constituents of the upper topsoil, physically based models are developed to quantify soil organic carbon, iron oxides and clay content. Taking account of the benefits limitations of existing methods, the approach is based on the direct application of known diagnostic spectral features and their combination with multivariate statistical approaches. It benefits from the collinearity of several diagnostic features and a number of their properties to reduce signal disturbances by influences of other spectral features. In a following step, the acquired hyperspectral image data are prepared for an analysis of soil constituents. The data show a large spatial heterogeneity that is caused by the patchiness of the natural vegetation in the study area that is inherent to most semiarid landscapes. Spectral mixture analysis is performed and used to deconvolve non-homogenous pixels into their constituent components. For soil dominated pixels, the subpixel information is used to remove the spectral influence of vegetation and to approximate the pure spectral signature coming from the soil. This step is an integral part when working in natural non-agricultural areas where pure bare soil pixels are rare. It is identified as the largest benefit within the multi-stage methodology, providing the basis for a successful and unbiased prediction of soil constituents from hyperspectral imagery. With the proposed approach it is possible (1) to significantly increase the spatial extent of derived information of soil constituents to areas with about 40 % vegetation coverage and (2) to reduce the influence of materials such as vegetation on the quantification of soil constituents to a minimum. Subsequently, soil parameter quantities are predicted by the application of the feature-based soil prediction models to the maps of locally approximated soil signatures. Thematic maps showing the spatial distribution of the three considered soil parameters in October 2009 are produced for the Albany Thicket Biome of South Africa. The maps are evaluated for their potential to detect erosion affected areas as effects of land changes and to identify degradation hot spots in regard to support local restoration efforts. A regional validation, carried out using available ground truth sites, suggests remaining factors disturbing the correlation of spectral characteristics and chemical soil constituents. The approach is developed for semiarid areas in general and not adapted to specific conditions in the study area. All processing steps of the developed methodology are implemented in software modules, where crucial steps of the workflow are fully automated. The transferability of the methodology is shown for simulated data of the future EnMAP hyperspectral satellite. Soil parameters are successfully predicted from these data despite intense spectral mixing within the lower spatial resolution EnMAP pixels. This study shows an innovative approach to use Imaging Spectroscopy for mapping of key soil constituents, including soil organic carbon, for large areas in a non-agricultural ecosystem and under consideration of a partially vegetation coverage. It can contribute to a better assessment of soil constituents that describe ecosystem processes relevant to detect and monitor land changes. The maps further provide an assessment of the current carbon inventory in soils, valuable for carbon balances and carbon mitigation products.
Die Elbe und ihr Einzugsgebiet sind vom Klimawandel betroffen. Um die Wirkkette von projizierten Klimaveränderungen auf den Wasserhaushalt und die daraus resultierenden Nährstoffeinträge und -frachten für große Einzugsgebiete wie das der Elbe zu analysieren, können integrierte Umweltmodellsysteme eingesetzt werden. Fallstudien, die mit diesen Modellsystemen ad hoc durchgeführt werden, repräsentieren den Istzustand von Modellentwicklungen und -unsicherheiten und sind damit statisch.
Diese Arbeit beschreibt den Einstieg in die Dynamisierung von Klimafolgenanalysen im Elbegebiet. Dies umfasst zum einen eine Plausibilitätsprüfung von Auswirkungsrechnungen, die mit Szenarien des statistischen Szenariengenerators STARS durchgeführt wurden, durch den Vergleich mit den Auswirkungen neuerer Klimaszenarien aus dem ISI-MIP Projekt, die dem letzten Stand der Klimamodellierung entsprechen. Hierfür wird ein integriertes Modellsystem mit "eingefrorenem Entwicklungsstand" verwendet. Die Klimawirkungsmodelle bleiben dabei unverändert. Zum anderen wird ein Bestandteil des integrierten Modellsystems – das ökohydrologische Modell SWIM – zu einer "live"-Version weiterentwickelt. Diese wird durch punktuelle Testung an langjährigen Versuchsreihen eines Lysimeterstandorts sowie an aktuellen Abflussreihen validiert und verbessert.
Folgende Forschungsfragen werden bearbeitet: (i) Welche Effekte haben unterschiedliche Klimaszenarien auf den Wasserhaushalt im Elbegebiet und ist eine Neubewertung der Auswirkung des Klimawandels auf den Wasserhaushalt notwendig?, (ii) Was sind die Auswirkungen des Klimawandels auf die Nährstoffeinträge und -frachten im Elbegebiet sowie die Wirksamkeit von Maßnahmen zur Reduktion der Nährstoffeinträge?, (iii) Ist unter der Nutzung (selbst einer sehr geringen Anzahl) verfügbarer tagesaktueller Witterungsdaten in einem stark heterogenen Einzugsgebiet eine valide Ansprache der aktuellen ökohydrologischen Situation des Elbeeinzugsgebiets möglich?
Die aktuellen Szenarien bestätigen die Richtung, jedoch nicht das Ausmaß der Klimafolgen: Die Rückgänge des mittleren jährlichen Gesamtabflusses und der monatlichen Abflüsse an den Pegeln bis Mitte des Jahrhunderts betragen für das STARS-Szenario ca. 30 %. Die Rückgänge bei den auf dem ISI-MIP-Szenario basierenden Modellstudien liegen hingegen nur bei ca. 10 %. Hauptursachen für diese Divergenz sind die Unterschiede in den Niederschlagsprojektionen sowie die Unterschiede in der jahreszeitlichen Verteilung der Erwärmung. Im STARS-Szenario gehen methodisch bedingt die Niederschläge zurück und der Winter erwärmt sich stärker als der Sommer. In dem ISI-MIP-Szenario bleiben die Niederschläge nahezu stabil und die Erwärmung im Sommer und Winter unterscheidet sich nur geringfügig.
Generell nehmen die Nährstoffeinträge und -frachten mit den Abflüssen in beiden Szenarien unterproportional ab, wobei die Frachten jeweils stärker als die Einträge zurückgehen. Die konkreten Effekte der Abflussänderungen sind gering und liegen im einstelligen Prozentbereich. Gleiches gilt für die Unterschiede zwischen den Szenarien. Der Effekt von zwei ausgewählten Maßnahmen zur Reduktion der Nährstoffeinträge und -frachten unterscheidet sich bei verschiedenen Abflussverhältnissen, repräsentiert durch unterschiedliche Klimaszenarien in unterschiedlich feuchter Ausprägung, ebenfalls nur geringfügig.
Die Beantwortung der ersten beiden Forschungsfragen zeigt, dass die Aktualisierung von Klimaszenarien in einem ansonsten "eingefrorenen" Verbund von ökohydrologischen Daten und Modellen eine wichtige Prüfoption für die Plausibilisierung von Klimafolgenanalysen darstellt. Sie bildet die methodische Grundlage für die Schlussfolgerung, dass bei der Wassermenge eine Neubewertung der Klimafolgen notwendig ist, während dies bei den Nährstoffeinträgen und -frachten nicht der Fall ist.
Die zur Beantwortung der dritten Forschungsfrage mit SWIM-live durchgeführten Validierungsstudien ergeben Diskrepanzen am Lysimeterstandort und bei den Abflüssen aus den Teilgebieten Saale und Spree. Sie lassen sich zum Teil mit der notwendigen Interpolationsweite der Witterungsdaten und dem Einfluss von Wasserbewirtschaftungsmaßnahmen erklären. Insgesamt zeigen die Validierungsergebnisse, dass schon die Pilotversion von SWIM-live für eine ökohydrologische Ansprache des Gebietswasserhaushaltes im Elbeeinzugsgebiet genutzt werden kann. SWIM-live ermöglicht eine unmittelbare Betrachtung und Beurteilung simulierter Daten. Dadurch werden Unsicherheiten bei der Modellierung direkt offengelegt und können infolge dessen reduziert werden. Zum einen führte die Verdichtung der meteorologischen Eingangsdaten durch die Verwendung von nun ca. 700 anstatt 19 Klima- bzw. Niederschlagstationen zu einer Verbesserung der Ergebnisse. Zum anderen wurde SWIM-live beispielhaft für einen Zyklus aus punktueller Modellverbesserung und flächiger Überprüfung der Simulationsergebnisse genutzt.
Die einzelnen Teilarbeiten tragen jeweils zur Dynamisierung von Klimafolgenanalysen im Elbegebiet bei. Der Anlass hierfür war durch die fehlerhaften methodischen Grundlagen von STARS gegeben. Die Sinnfälligkeit der Dynamisierung ist jedoch nicht an diesen konkreten Anlass gebunden, sondern beruht auf der grundlegenden Einsicht, dass Ad-hoc-Szenarienanalysen immer auch pragmatische Vereinfachungen zugrunde liegen, die fortlaufend überprüft werden müssen.
This thesis investigates how the permafrost microbiota responds to global warming. In detail, the constraints behind methane production in thawing permafrost were linked to methanogenic activity, abundance and composition. Furthermore, this thesis offers new insights into microbial adaptions to the changing environmental conditions during global warming. This was assesed by investigating the potential ecological relevant functions encoded by plasmid DNA within the permafrost microbiota. Permafrost of both interglacial and glacial origin spanning the Holocene to the late Pleistocene, including Eemian, were studied during long-term thaw incubations. Furthermore, several permafrost cores of different stratigraphy, soil type and vegetation cover were used to target the main constraints behind methane production during short-term thaw simulations. Short- and long-term incubations simulating thaw with and without the addition of substrate were combined with activity measurements, amplicon and metagenomic sequencing of permanently frozen and seasonally thawed active layer. Combined, it allowed to address the following questions. i) What constraints methane production when permafrost thaws and how is this linked to methanogenic activity, abundance and composition? ii) How does the methanogenic community composition change during long-term thawing conditions? iii) Which potential ecological relevant functions are encoded by plasmid DNA in active layer soils?
The major outcomes of this thesis are as follows. i) Methane production from permafrost after long-term thaw simulation was found to be constrained mainly by the abundance of methanogens and the archaeal community composition. Deposits formed during periods of warmer temperatures and increased precipitation, (here represented by deposits from the Late Pleistocene of both interstadial and interglacial periods) were found to respond strongest to thawing conditions and to contain an archaeal community dominated by methanogenic archaea (40% and 100% of all detected archaea). Methanogenic population size and carbon density were identified as main predictors for potential methane production in thawing permafrost in short-term incubations when substrate was sufficiently available.
ii) Besides determining the methanogenic activity after long-term thaw, the paleoenvironmental conditions were also found to influence the response of the methanogenic community composition. Substantial shifts within methanogenic community structure and a drop in diversity were observed in deposits formed during warmer periods, but not in deposits from stadials, when colder and drier conditions occurred. Overall, a shift towards a dominance of hydrogenotrophic methanogens was observed in all samples, except for the oldest interglacial deposits from the Eemian, which displayed a potential dominance of acetoclastic methanogens. The Eemian, which is discussed to serve as an analogue to current climate conditions, contained highly active methanogenic communities. However, all potential limitation of methane production after permafrost thaw, it means methanogenic community structure, methanogenic population size, and substrate pool might be overcome after permafrost had thawed on the long-term. iii) Enrichments with soil from the seasonally thawed active layer revealed that its plasmid DNA (‘metaplasmidome’) carries stress-response genes. In particular it encoded antibiotic resistance genes, heavy metal resistance genes, cold shock proteins and genes encoding UV-protection. Those are functions that are directly involved in the adaptation of microbial communities to stresses in polar environments. It was further found that metaplasmidomes from the Siberian active layer originate mainly from Gammaproteobacteria. By applying enrichment cultures followed by plasmid DNA extraction it was possible to obtain a higher average contigs length and significantly higher recovery of plasmid sequences than from extracting plasmid sequences from metagenomes. The approach of analyzing ‘metaplasmidomes’ established in this thesis is therefore suitable for studying the ecological role of plasmids in polar environments in general.
This thesis emphasizes that including microbial community dynamics have the potential to improve permafrost-carbon projections. Microbially mediated methane release from permafrost environments may significantly impact future climate change. This thesis identified drivers of methanogenic composition, abundance and activity in thawing permafrost landscapes. Finally, this thesis underlines the importance to study how the current warming Arctic affects microbial communities in order to gain more insight into microbial response and adaptation strategies.
The increase in atmospheric methane concentration, which is determined by an imbalance between its sources and sinks, has led to investigations of the methane cycle in various environments. Aquatic environments are of an exceptional interest due to their active involvement in methane cycling worldwide and in particular in areas sensitive to climate change. Furthermore, being connected with each other aquatic environments form networks that can be spread on vast areas involving marine, freshwater and terrestrial ecosystems. Thus, aquatic systems have a high potential to translate local or regional environmental and subsequently ecosystem changes to a bigger scale. Many studies neglect this connectivity and focus on individual aquatic or terrestrial ecosystems.
The current study focuses on environmental controls of the distribution and aerobic oxidation of methane at the example of two aquatic ecosystems. These ecosystems are Arctic fresh water bodies and the Elbe estuary which represent interfaces between freshwater-terrestrial and freshwater-marine environments, respectively.
Arctic water bodies are significant atmospheric sources of methane. At the same time the methane cycle in Arctic water bodies is strongly affected by the surrounding permafrost environment, which is characterized by high amounts of organic carbon. The results of this thesis indicate that the methane concentrations in Arctic lakes and streams substantially vary between each other being regulated by local landscape features (e.g. floodplain area) and the morphology of the water bodies (lakes, streams and river). The highest methane concentrations were detected in the lake outlets and in a floodplain lake complex. In contrast, the methane concentrations measured at different sites of the Lena River did not vary substantially. The lake complexes in comparison to the Lena River, thus, appear as more individual and heterogeneous systems with a pronounced imprint of the surrounding soil environment. Furthermore, connected with each other Arctic aquatic environments have a large potential to transport methane from methane-rich water bodies such as streams and floodplain lakes to aquatic environments relatively poor in methane such as the Lena River.
Estuaries represent hot spots of oceanic methane emissions. Also, estuaries are intermediate zones between methane-rich river water and methane depleted marine water. Substantiated through this thesis at the example of the Elbe estuary, the methane distribution in estuaries, however, cannot entirely be described by the conservative mixing model i.e. gradual decrease from the freshwater end-member to the marine water end-member. In addition to the methane-rich water from the Elbe River mouth substantial methane input occurs from tidal flats, areas of significant interaction between aquatic and terrestrial environments. Thus, this study demonstrates the complex interactions and their consequences for the methane distribution within estuaries. Also it reveals how important it is to investigate estuaries at larger spatial scales.
Methane oxidation (MOX) rates are commonly correlated with methane concentrations. This was shown in previous research studies and was substantiated by the present thesis. In detail, the highest MOX rates in the Arctic water bodies were detected in methane-rich streams and in the floodplain area while in the Elbe estuary the highest MOX rates were observed at the coastal stations. However, in these bordering environments, MOX rates are affected not only via the regulation through methane concentrations. The MOX rates in the Arctic lakes were shown to be also dependent on the abundance and community composition of methane-oxidising bacteria (MOB), that in turn are controlled by local landscape features (regardless of the methane concentrations) and by the transport of MOB between neighbouring environments. In the Elbe estuary, the MOX rates in addition to the methane concentrations are largely affected by the salinity, which is in turn regulated by the mixing of fresh- and marine waters. The magnitude of the salinity impact on MOX rates thereby depends on the MOB community composition and on the rate of the salinity change.
This study extends our knowledge of environmental controls of methane distribution and aerobic methane oxidation in aquatic environments. It also illustrates how important it is to investigate complex ecosystems rather than individual ecosystems to better understand the functioning of whole biomes.