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Gas hydrates are ice-like crystalline compounds made of water cavities that retain various types of guest molecules. Natural gas hydrates are CH4-rich but also contain higher hydrocarbons as well as CO2, H2S, etc. They are highly dependent of local pressure and temperature conditions. Considering the high energy content, natural gas hydrates are artificially dissociated for the production of methane gas. Besides, they may also dissociate in response to global warming. It is therefore crucial to investigate the hydrate nucleation and growth process at a molecular level. The understanding of how guest molecules in the hydrate cavities respond to warming climate or gas injection is also of great importance.
This thesis is concerned with a systematic investigation of simple and mixed gas hydrates at conditions relevant to the natural hydrate reservoir in Qilian Mountain permafrost, China. A high-pressure cell that integrated into the confocal Raman spectroscopy ensured a precise and continuous characterization of the hydrate phase during formation/dissociation/transformation processes with a high special and spectral resolution. By applying laboratory experiments, the formation of mixed gas hydrates containing other hydrocarbons besides methane was simulated in consideration of the effects from gas supply conditions and sediments. The results revealed a preferential enclathration of different guest molecules in hydrate cavities and further refute the common hypothesis of the coexistence of hydrate phases due to a changing feed gas phase. However, the presence of specific minerals and organic compounds in sediments may have significant impacts on the coexisting solid phases. With regard to the dissociation, the formation damage caused by fines mobilization and migration during hydrate decomposition was reported for the first time, illustrating the complex interactions between fine grains and hydrate particles. Gas hydrates, starting from simple CH4 hydrates to binary CH4—C3H8 hydrates and multi-component mixed hydrates were decomposed by thermal stimulation mimicking global warming. The mechanisms of guest substitution in hydrate structures were studied through the experimental data obtained from CH4—CO2, CH4—mixed gas hydrates and mixed gas hydrates—CO2 systems. For the first time, a second transformation behavior was documented during the transformation process from CH4 hydrates to CO2-rich mixed hydrates. Most of the crystals grew or maintained when exposed to CO2 gas while some others decreased in sizes and even disappeared over time. The highlight of the two last experimental simulations was to visualize and characterize the hydrate crystals which were at different structural transition stages. These experimental simulations enhanced our knowledge about the mixed gas hydrates in natural reservoirs and improved our capability to assess the response to global warming.
Technological progress allows for producing ever more complex predictive models on the basis of increasingly big datasets. For risk management of natural hazards, a multitude of models is needed as basis for decision-making, e.g. in the evaluation of observational data, for the prediction of hazard scenarios, or for statistical estimates of expected damage. The question arises, how modern modelling approaches like machine learning or data-mining can be meaningfully deployed in this thematic field. In addition, with respect to data availability and accessibility, the trend is towards open data. Topic of this thesis is therefore to investigate the possibilities and limitations of machine learning and open geospatial data in the field of flood risk modelling in the broad sense. As this overarching topic is broad in scope, individual relevant aspects are identified and inspected in detail.
A prominent data source in the flood context is satellite-based mapping of inundated areas, for example made openly available by the Copernicus service of the European Union. Great expectations are directed towards these products in scientific literature, both for acute support of relief forces during emergency response action, and for modelling via hydrodynamic models or for damage estimation. Therefore, a focus of this work was set on evaluating these flood masks. From the observation that the quality of these products is insufficient in forested and built-up areas, a procedure for subsequent improvement via machine learning was developed. This procedure is based on a classification algorithm that only requires training data from a particular class to be predicted, in this specific case data of flooded areas, but not of the negative class (dry areas). The application for hurricane Harvey in Houston shows the high potential of this method, which depends on the quality of the initial flood mask.
Next, it is investigated how much the predicted statistical risk from a process-based model chain is dependent on implemented physical process details. Thereby it is demonstrated what a risk study based on established models can deliver. Even for fluvial flooding, such model chains are already quite complex, though, and are hardly available for compound or cascading events comprising torrential rainfall, flash floods, and other processes. In the fourth chapter of this thesis it is therefore tested whether machine learning based on comprehensive damage data can offer a more direct path towards damage modelling, that avoids explicit conception of such a model chain. For that purpose, a state-collected dataset of damaged buildings from the severe El Niño event 2017 in Peru is used. In this context, the possibilities of data-mining for extracting process knowledge are explored as well. It can be shown that various openly available geodata sources contain useful information for flood hazard and damage modelling for complex events, e.g. satellite-based rainfall measurements, topographic and hydrographic information, mapped settlement areas, as well as indicators from spectral data. Further, insights on damaging processes are discovered, which mainly are in line with prior expectations. The maximum intensity of rainfall, for example, acts stronger in cities and steep canyons, while the sum of rain was found more informative in low-lying river catchments and forested areas. Rural areas of Peru exhibited higher vulnerability in the presented study compared to urban areas. However, the general limitations of the methods and the dependence on specific datasets and algorithms also become obvious.
In the overarching discussion, the different methods – process-based modelling, predictive machine learning, and data-mining – are evaluated with respect to the overall research questions. In the case of hazard observation it seems that a focus on novel algorithms makes sense for future research. In the subtopic of hazard modelling, especially for river floods, the improvement of physical models and the integration of process-based and statistical procedures is suggested. For damage modelling the large and representative datasets necessary for the broad application of machine learning are still lacking. Therefore, the improvement of the data basis in the field of damage is currently regarded as more important than the selection of algorithms.
Enhanced geothermal systems (EGS) are considered a cornerstone of future sustainable energy production. In such systems, high-pressure fluid injections break the rock to provide pathways for water to circulate in and heat up. This approach inherently induces small seismic events that, in rare cases, are felt or can even cause damage. Controlling and reducing the seismic impact of EGS is crucial for a broader public acceptance. To evaluate the applicability of hydraulic fracturing (HF) in EGS and to improve the understanding of fracturing processes and the hydromechanical relation to induced seismicity, six in-situ, meter-scale HF experiments with different injection schemes were performed under controlled conditions in crystalline rock in a depth of 410 m at the Äspö Hard Rock Laboratory (Sweden).
I developed a semi-automated, full-waveform-based detection, classification, and location workflow to extract and characterize the acoustic emission (AE) activity from the continuous recordings of 11 piezoelectric AE sensors. Based on the resulting catalog of 20,000 AEs, with rupture sizes of cm to dm, I mapped and characterized the fracture growth in great detail. The injection using a novel cyclic injection scheme (HF3) had a lower seismic impact than the conventional injections. HF3 induced fewer AEs with a reduced maximum magnitude and significantly larger b-values, implying a decreased number of large events relative to the number of small ones. Furthermore, HF3 showed an increased fracture complexity with multiple fractures or a fracture network. In contrast, the conventional injections developed single, planar fracture zones (Publication 1).
An independent, complementary approach based on a comparison of modeled and observed tilt exploits transient long-period signals recorded at the horizontal components of two broad-band seismometers a few tens of meters apart from the injections. It validated the efficient creation of hydraulic fractures and verified the AE-based fracture geometries. The innovative joint analysis of AEs and tilt signals revealed different phases of the fracturing process, including the (re-)opening, growth, and aftergrowth of fractures, and provided evidence for the reactivation of a preexisting fault in one of the experiments (Publication 2). A newly developed network-based waveform-similarity analysis applied to the massive AE activity supports the latter finding.
To validate whether the reduction of the seismic impact as observed for the cyclic injection schemes during the Äspö mine-scale experiments is transferable to other scales, I additionally calculated energy budgets for injection experiments from previously conducted laboratory tests and from a field application. Across all three scales, the cyclic injections reduce the seismic impact, as depicted by smaller maximum magnitudes, larger b-values, and decreased injection efficiencies (Publication 3).
Localisation of deformation is a ubiquitous feature in continental rift dynamics and observed across drastically different time and length scales. This thesis comprises one experimental and two numerical modelling studies investigating strain localisation in (1) a ductile shear zone induced by a material heterogeneity and (2) in an active continental rift setting. The studies are related by the fact that the weakening mechanisms on the crystallographic and grain size scale enable bulk rock weakening, which fundamentally enables the formation of shear zones, continental rifts and hence plate tectonics. Aiming to investigate the controlling mechanisms on initiation and evolution of a shear zone, the torsion experiments of the experimental study were conducted in a Patterson type apparatus with strong Carrara marble cylinders with a weak, planar Solnhofen limestone inclusion. Using state-of-the-art numerical modelling software, the torsion experiments were simulated to answer questions regarding localisation procedure like stress distribution or the impact of rheological weakening. 2D numerical models were also employed to integrate geophysical and geological data to explain characteristic tectonic evolution of the Southern and Central Kenya Rift. Key elements of the numerical tools are a randomized initial strain distribution and the usage of strain softening. During the torsion experiments, deformation begins to localise at the limestone inclusion tips in a process zone, which propagates into the marble matrix with increasing deformation until a ductile shear zone is established. Minor indicators for coexisting brittle deformation are found close to the inclusion tip and presumed to slightly facilitate strain localisation besides the dominant ductile deformation processes. The 2D numerical model of the torsion experiment successfully predicts local stress concentration and strain rate amplification ahead of the inclusion in first order agreement with the experimental results. A simple linear parametrization of strain weaking enables high accuracy reproduction of phenomenological aspects of the observed weakening. The torsion experiments suggest that loading conditions do not affect strain localisation during high temperature deformation of multiphase material with high viscosity contrasts. A numerical simulation can provide a way of analysing the process zone evolution virtually and extend the examinable frame. Furthermore, the nested structure and anastomosing shape of an ultramylonite band was mimicked with an additional second softening step. Rheological weakening is necessary to establish a shear zone in a strong matrix around a weak inclusion and for ultramylonite formation.
Such strain weakening laws are also incorporated into the numerical models of the
Southern and Central Kenya Rift that capture the characteristic tectonic evolution. A three-stage early rift evolution is suggested that starts with (1) the accommodation of strain by a single border fault and flexure of the hanging-wall crust, after which (2) faulting in the hanging-wall and the basin centre increases before (3) the early-stage asymmetry is lost and basinward localisation of deformation occurs. Along-strike variability of rifts can be produced by modifying the initial random noise distribution. In summary, the three studies address selected aspects of the broad range of mechanisms and processes that fundamentally enable the deformation of rock and govern the localisation patterns across the scales. In addition to the aforementioned results, the first and second manuscripts combined, demonstrate a procedure to find new or improve on existing numerical formulations for specific rheologies and their dynamic weakening. These formulations are essential in addressing rock deformation from the grain to the global scale. As within the third study of this thesis, where geodynamic controls on the evolution of a rift were examined and acquired by the integration of geological and geophysical data into a numerical model.
Processes driving the production, transformation and transport of methane (CH4 / in wetland ecosystems are highly complex. We present a simple calculation algorithm to separate open-water CH4 fluxes measured with automatic chambers into diffusion-and ebullition-derived components. This helps to reveal underlying dynamics, to identify potential environmental drivers and, thus, to calculate reliable CH4 emission estimates. The flux separation is based on identification of ebullition-related sudden concentration changes during single measurements. Therefore, a variable ebullition filter is applied, using the lower and upper quartile and the interquartile range (IQR). Automation of data processing is achieved by using an established R script, adjusted for the purpose of CH4 flux calculation. The algorithm was validated by performing a laboratory experiment and tested using flux measurement data (July to September 2013) from a former fen grassland site, which converted into a shallow lake as a result of rewetting. Ebullition and diffusion contributed equally (46 and 55 %) to total CH4 emissions, which is comparable to ratios given in the literature. Moreover, the separation algorithm revealed a concealed shift in the diurnal trend of diffusive fluxes throughout the measurement period. The water temperature gradient was identified as one of the major drivers of diffusive CH4 emissions, whereas no significant driver was found in the case of erratic CH4 ebullition events.
We investigate source processes of fluid-induced seismicity from The Geysers geothermal reservoir in California to determine their relation with hydraulic operations and improve the corresponding seismic hazard estimates. Analysis of 869 well-constrained full moment tensors (M-w 0.8-3.5) reveals significant non-double-couple components (>25%) for about 65% of the events. Volumetric deformation is governed by cumulative injection rates with larger non-double-couple components observed near the wells and during high injection periods. Source mechanisms are magnitude dependent and vary significantly between faulting regimes. Normal faulting events (M-w<2) reveal substantial volumetric components indicating dilatancy in contrast to strike-slip events that have a dominant double-couple source. Volumetric components indicating closure of cracks in the source region are mostly found for reverse faulting events with M-w>2.5. Our results imply that source processes and magnitudes of fluid-induced seismic events are strongly affected by the hydraulic operations, the reservoir stress state, and the faulting regime.
Fragmentation of landscapes creates a transition zone in between natural habitats or different kinds of land use. In forested and agricultural landscapes with transition zones, microclimate and matter cycling are markedly altered. This probably accelerates and is intensified by global warming. However, there is no consensus on defining transition zones and quantifying relevant variables for microclimate and matter cycling across disciplines. This article is an attempt to a) revise definitions and offer a framework for quantitative ecologists, b) review the literature on microclimate and matter cycling in transition zones and c) summarise this information using meta-analysis to better understand bio-geochemical and bio-geophysical processes and their spatial extent in transition zones. We expect altered conditions in soils of transition zones to be 10-20 m with a maximum of 50 m, and 25-50 m for above-ground space with a maximum of 125 m.
We present a high-resolution study of the upper mantle structure of Central Europe, including the western part of the East European Platform, based on S-receiver functions of 345 stations. A distinct contrast is found between Phanerozoic Europe and the East European Craton across the Trans-European Suture Zone. To the west, a pronounced velocity reduction with depth interpreted as lithosphere-asthenosphere boundary (LAB) is found at an average depth of 90 km. Beneath the craton, no strong and continuous LAB conversion is observed. Instead we find a distinct velocity reduction within the lithosphere, at 80-120 km depth. This mid-lithospheric discontinuity (MLD) is attributed to a compositional boundary between depleted and more fertile lithosphere created by late Proterozoic metasomatism. A potential LAB phase beneath the craton is very weak and varies in depth between 180 and 250 km, consistent with a reduced velocity contrast between the lower lithosphere and the asthenosphere. Within the Trans-European Suture Zone, lithospheric structure is characterized by strong heterogeneity. A dipping or step-wise increase to LAB depth of 150 km is imaged from Phanerozoic Europe to 20-22 degrees E, whereas no direct connection to the cratonic LAB or MLD to the east is apparent. At larger depths, a positive conversion associated with the lower boundary of the asthenosphere is imaged at 210-250 km depth beneath Phanerozoic Europe, continuing down to 300 km depth beneath the craton. Conversions from both 410 km and 660 km discontinuities are found at their nominal depth beneath Phanerozoic Europe, and the discontinuity at 410 km depth can also be traced into the craton. A potential negative conversion on top of the 410 km discontinuity found in migrated images is analyzed by modeling and attributed to interference with other converted phases.
The Kenya rift revisited
(2017)
We present three-dimensional (3-D) models that describe the present-day thermal and rheological state of the lithosphere of the greater Kenya rift region aiming at a better understanding of the rift evolution, with a particular focus on plume-lithosphere interactions. The key methodology applied is the 3-D integration of diverse geological and geophysical observations using gravity modelling. Accordingly, the resulting lithospheric-scale 3-D density model is consistent with (i) reviewed descriptions of lithological variations in the sedimentary and volcanic cover, (ii) known trends in crust and mantle seismic velocities as revealed by seismic and seismological data and (iii) the observed gravity field. This data-based model is the first to image a 3-D density configuration of the crystalline crust for the entire region of Kenya and northern Tanzania. An upper and a basal crustal layer are differentiated, each composed of several domains of different average densities. We interpret these domains to trace back to the Precambrian terrane amalgamation associated with the East African Orogeny and to magmatic processes during Mesozoic and Cenozoic rifting phases. In combination with seismic velocities, the densities of these crustal domains indicate compositional differences. The derived lithological trends have been used to parameterise steady-state thermal and rheological models. These models indicate that crustal and mantle temperatures decrease from the Kenya rift in the west to eastern Kenya, while the integrated strength of the lithosphere increases. Thereby, the detailed strength configuration appears strongly controlled by the complex inherited crustal structure, which may have been decisive for the onset, localisation and propagation of rifting.
Moderate to large earthquakes can increase the amount of water feeding stream flows, mobilizing excess water from deep groundwater, shallow groundwater, or the vadose zone. Here we examine the regional pattern of streamflow response to the Maule M8.8 earthquake across Chile's diverse topographic and hydro-climatic gradients. We combine streamflow analyses with groundwater flow modeling and a random forest classifier, and find that, after the earthquake, at least 85 streams had a change in flow. Discharge mostly increased () shortly after the earthquake, liberating an excess water volume of >1.1 km3, which is the largest ever reported following an earthquake. Several catchments had increased discharge of >50 mm, locally exceeding seasonal streamflow discharge under undisturbed conditions. Our modeling results favor enhanced vertical permeability induced by dynamic strain as the most probable process explaining the observed changes at the regional scale. Supporting this interpretation, our random forest classification identifies peak ground velocity and elevation extremes as most important for predicting streamflow response. Given the mean recurrence interval of ∼25 yr for >M8.0 earthquakes along the Peru–Chile Trench, our observations highlight the role of earthquakes in the regional water cycle, especially in arid environments.
Temporal and spatial stability of the vegetation climate relationship is a basic ecological assumption for pollen-based quantitative inferences of past climate change and for predicting future vegetation. We explore this assumption for the Holocene in eastern continental Asia (China, Mongolia). Boosted regression trees (BRT) between fossil pollen taxa percentages (Abies, Artemisia, Betula, Chenopodiaceae, Cyperaceae, Ephedra, Picea, Pinus, Poaceae and Quercus) and climate model outputs of mean annual precipitation (P-ann) and mean temperature of the warmest month (Mt(wa)) for 9 and 6 ka (ka = thousand years before present) were set up and results compared to those obtained from relating modern pollen to modern climate. Overall, our results reveal only slight temporal differences in the pollen climate relationships. Our analyses suggest that the importance of P-ann compared with Mt(wa) for taxa distribution is higher today than it was at 6 ka and 9 ka. In particular, the relevance of P-ann for Picea and Pinus increases and has become the main determinant. This change in the climate tree pollen relationship parallels a widespread tree pollen decrease in north-central China and the eastern Tibetan Plateau. We assume that this is at least partly related to vegetation climate disequilibrium originating from human impact. Increased atmospheric CO2 concentration may have permitted the expansion of moisture-loving herb taxa (Cyperaceae and Poaceae) during the late Holocene into arid/semi-arid areas. We furthermore find that the pollen climate relationship between north-central China and the eastern Tibetan Plateau is generally similar, but that regional differences are larger than temporal differences. In summary, vegetation climate relationships in China are generally stable in space and time, and pollen-based climate reconstructions can be applied to the Holocene. Regional differences imply the calibration-set should be restricted spatially.
Landscape evolution models (LEMs) allow the study of earth surface responses to changing climatic and tectonic forcings. While much effort has been devoted to the development of LEMs that simulate a wide range of processes, the numerical accuracy of these models has received less attention. Most LEMs use first-order accurate numerical methods that suffer from substantial numerical diffusion. Numerical diffusion particularly affects the solution of the advection equation and thus the simulation of retreating landforms such as cliffs and river knickpoints. This has potential consequences for the integrated response of the simulated landscape. Here we test a higher-order flux-limiting finite volume method that is total variation diminishing (TVD-FVM) to solve the partial differential equations of river incision and tectonic displacement. We show that using the TVD-FVM to simulate river incision significantly influences the evolution of simulated landscapes and the spatial and temporal variability of catchment-wide erosion rates. Furthermore, a two-dimensional TVD-FVM accurately simulates the evolution of landscapes affected by lateral tectonic displacement, a process whose simulation was hitherto largely limited to LEMs with flexible spatial discretization. We implement the scheme in TTLEM (TopoToolbox Landscape Evolution Model), a spatially explicit, raster-based LEM for the study of fluvially eroding landscapes in TopoToolbox 2.
Along a subduction zone, great megathrust earthquakes recur either after long seismic gaps lasting several decades to centuries or over much shorter periods lasting hours to a few years when cascading successions of earthquakes rupture nearby segments of the fault. We analyze a decade of continuous Global Positioning System observations along the South American continent to estimate changes in deformation rates between the 2010 Maule (M8.8) and 2015 Illapel (M8.3) Chilean earthquakes. We find that surface velocities increased after the 2010 earthquake, in response to continental-scale viscoelastic mantle relaxation and to regional-scale increased degree of interplate locking. We propose that increased locking occurs transiently during a super-interseismic phase in segments adjacent to a megathrust rupture, responding to bending of both plates caused by coseismic slip and subsequent afterslip. Enhanced strain rates during a super-interseismic phase may therefore bring a megathrust segment closer to failure and possibly triggered the 2015 event.
Atmospheric transport is an understudied mechanism for leaf wax hydrogen isotope applications that contributes to mobilizing and depositing these compounds on the surface of the Earth. While previous efforts have identified the importance of atmospheric leaf wax deposition in remote marine locations, the processes are not well constrained on land in temperate latitudes where lakes are common and sedimentary leaf wax hydrogen isotope values are an attractive tool for understanding past precipitation changes. This work presents results from a field study that was conducted in 2010 and 2011 at Hainich National Park, Germany in order to evaluate the quantity and sources of leaf waxes in the atmosphere. Aerosols were sampled at approximately weekly intervals inside the forest canopy, and n-alkane distributions and hydrogen isotope values were compared with those from major tree species surrounding the sampling site. Despite sampling in what was expected to be a major production center, the distribution and hydrogen isotope values of atmospheric n-alkanes bore little resemblance to those of the local vegetation. Comparison with local meteorological data and to 10-day and 36-h back air mass trajectories indicated shifting effects of winds and temperature, and that mesoscale transport processes were more important than longrange mechanisms. Back trajectories also highlighted source effects, with easterly winds coinciding with relatively lower leaf wax hydrogen isotope values from more continental regions. These results suggest that leaf wax aerosols average over spatial scales that exceed typical surface catchment areas for small lake systems, even in forested areas, yet that the area over which these compounds are derived is still relatively regional. Depositional fluxes were also estimated in order to assess the potential importance of atmospheric transport to sedimentary archives. Although difficult to constrain, these estimates suggest that atmospheric deposition may be non-negligible for lake systems in cases where inputs from rivers or surface runoff are limited. Together, these observations provide new insights on how leaf waxes from different sources are integrated during aeolian transport and the spatial scales over which these processes occur.
Sensitivity and identifiability analyses are common diagnostic tools to address over-parametrization in complex environmental models, but a combined application of the two analyses is rarely conducted. In this study, we performed a temporal global sensitivity analysis using the variance-based method of Sobol’ and a temporal identifiability analysis of model parameters using the dynamic identifiability method (DYNIA). We discuss the relationship between the two analyses with a focus on parameter identification and output uncertainty reduction. The hydrological model HydroGeoSphere was used to simulate daily evapotranspiration, water content, and seepage at the lysimeter scale. We found that identifiability of a parameter does not necessarily reduce output uncertainty. It was also found that the information from the main and total effects (main Sobol' sensitivity indices) is required to allow uncertainty reduction in the model output. Overall, the study highlights the role of combined temporal diagnostic tools for improving our understanding of model behavior.
The present-day vegetation in the tropics is mainly characterized by forests worldwide except in tropical East Africa, where forests only occur as patches at the coast and in the uplands. These forest patches result from the peculiar aridity that is linked to the uplift of the region during the Late Cenozoic. The Late Cenozoic vegetation history of East Africa is of particular interest as it has set the scene for the contemporary events in mammal and hominin evolution. In this study, we investigate the conditions under which these forest patches could have been connected, and a previous continuous forest belt could have extended and fragmented. We apply a dynamic vegetation model with a set of climatic scenarios in which we systematically alter the present-day environmental conditions such that they would be more favourable for a continuous forest belt in tropical East Africa. We consider varying environmental factors, namely temperature, precipitation and atmospheric CO2 concentrations. Our results show that all of these variables play a significant role in supporting the forest biomes and a continuous forest belt could have occurred under certain combinations of these settings. With our current knowledge of the palaeoenvironmental history of East Africa, it is likely that the region hosted these conditions during the Late Cenozoic. Recent improvements on environmental hypotheses of hominin evolution highlight the role of periods of short and extreme climate variability during the Late Cenozoic specific to East Africa in driving evolution. Our results elucidate how the forest biomes of East Africa can appear and disappear under fluctuating environmental conditions and demonstrate how this climate variability might be recognized on the biosphere level.
The African Humid Period (AHP) between similar to 15 and 5.5 cal. kyr BP caused major environmental change in East Africa, including filling of the Suguta Valley in the northern Kenya Rift with an extensive (similar to 2150 km(2)), deep (similar to 300 m) lake. Interfingering fluvio-lacustrine deposits of the Baragoi paleo-delta provide insights into the lake-level history and how erosion rates changed during this time, as revealed by delta-volume estimates and the concentration of cosmogenic Be-10 in fluvial sand. Erosion rates derived from delta-volume estimates range from 0.019 to 0.03 mm yr(-1). Be-10-derived paleo-erosion rates at similar to 11.8 cal. kyr BP ranged from 0.035 to 0.086 mm yr(-1), and were 2.7 to 6.6 times faster than at present. In contrast, at similar to 8.7 cal. kyr BP, erosion rates were only 1.8 times faster than at present. Because Be-10-derived erosion rates integrate over several millennia; we modeled the erosion-rate history that best explains the 10Be data using established non-linear equations that describe in situ cosmogenic isotope production and decay. Two models with different temporal constraints (15-6.7 and 12-6.7 kyr) suggest erosion rates that were 25 to 300 times higher than the initial erosion rate (pre-delta formation). That pulse of high erosion rates was short (similar to 4 kyr or less) and must have been followed by a rapid decrease in rates while climate remained humid to reach the modern Be-10-based erosion rate of,similar to 0.013 mm yr(-1). Our simulations also flag the two highest Be-10-derived erosion rates at 11.8 kyr BP related to nonuniform catchment erosion. These changes in erosion rates and processes during the AHP may reflect a strong increase in precipitation, runoff, and erosivity at the arid-to-humid transition either at 15 or similar to 12 cal. kyr BP, before the landscape stabilized again, possibly due to increased soil production and denser vegetation.
We analyse current and possible future reforms of the Indian food policies for the most important staple grains, wheat and rice, within a two-commodity dynamic partial equilibrium model with stochastic shocks. The model is empirically grounded and reproduces past values well. It uses a new reduced-form approach to capture private storage dynamics. We evaluate the implementation of the National Food Security Act (NFSA) under several policy measures with the current regime as well as two scenarios with a regime change - implementation of cash transfers and deficiency payments. Implications for market fundamentals and fiscal costs are simulated in the medium term - until 2020/21. The NFSA puts a high pressure on fiscal costs and public stocks. Relying on imports with low support prices results in low fiscal costs and stable, but higher domestic and international prices, and a high risk of zero stocks. A policy strategy to manipulate procurement prices in order to maintain public stocks close to the norms leads to slightly higher fiscal costs with lower, but more volatile prices. The highest domestic price volatility occurs under a strategy which uses export bans in order to maintain sufficient public stocks. A cash-based regime can bring considerable savings and curb fiscal costs, particularly if targeted to the poor, and would leave sufficient stocks due to higher private stocks.
The eastern flanks of the Central Andes are characterized by deep convection, exposing them to hydrometeorological extreme events, often resulting in floods and a variety of mass movements. We assessed the spatiotemporal pattern of rainfall trends and the changes in the magnitude and frequency of extreme events (ae<yen>95th percentile) along an E-W traverse across the southern Central Andes using rain-gauge and high-resolution gridded datasets (CPC-uni and TRMM 3B42 V7). We generated different climate indices and made three key observations: (1) an increase of the annual rainfall has occurred at the transition between low (< 0.5 km) and intermediate (0.5-3 km) elevations between 1950 and 2014. Also, rainfall increases during the wet season and, to a lesser degree, decreases during the dry season. Increasing trends in annual total amounts characterize the period 1979-2014 in the arid, high-elevation southern Andean Plateau, whereas trend reversals with decreasing annual total amounts were found at low elevations. (2) For all analyzed periods, we observed small or no changes in the median values of the rainfall-frequency distribution, but significant trends with intensification or attenuation in the 95th percentile. (3) In the southern Andean Plateau, extreme rainfall events exhibit trends towards increasing magnitude and, to a lesser degree, frequency during the wet season, at least since 1979. Our analysis revealed that low (< 0.5 km), intermediate (0.5-3 km), and high-elevation (> 3 km) areas respond differently to changing climate conditions, and the transition zone between low and intermediate elevations is characterized by the most significant changes.
Near-surface geophysical techniques are extensively used in a variety of engineering, environmental, geologic, and hydrologic applications. While many of these applications ask for detailed, quantitative models of selected material properties, geophysical data are increasingly used to estimate such target properties. Typically, this estimation procedure relies on a two-step workflow including (1) the inversion of geophysical data and (2) the petrophysical translation of the inverted parameter models into the target properties. Standard deterministic implementations of such a quantitative interpretation result in a single best-estimate model, often without considering and propagating the uncertainties related to the two steps. We address this problem by using a rather novel, particle-swarm-based global joint strategy for data inversion and by implementing Monte Carlo procedures for petrophysical property estimation. We apply our proposed workflow to crosshole ground-penetrating radar, P-, and S-wave data sets collected at a well-constrained test site for a detailed geotechnical characterization of unconsolidated sands. For joint traveltime inversion, the chosen global approach results in ensembles of acceptable velocity models, which are analyzed to appraise inversion-related uncertainties. Subsequently, the entire ensembles of inverted velocity models are considered to estimate selected petrophysical properties including porosity, bulk density, and elastic moduli via well-established petrophysical relations implemented in a Monte Carlo framework. Our results illustrate the potential benefit of such an advanced interpretation strategy; i.e., the proposed workflow allows to study how uncertainties propagate into the finally estimated property models, while concurrently we are able to study the impact of uncertainties in the used petrophysical relations (e.g., the influence of uncertain, user-specified parameters). We conclude that such statistical approaches for the quantitative interpretation of geophysical data can be easily extended and adapted to other applications and geophysical methods and might be an important step toward increasing the popularity and acceptance of geophysical tools in engineering practice.
Global earthquake locations are often associated with very large systematic travel-time residuals even for clear arrivals, especially for regional and near-regional stations in subduction zones because of their strongly heterogeneous velocity structure. Travel-time corrections can drastically reduce travel-time residuals at regional stations and, in consequence, improve the relative location accuracy. We have extended the shrinking-box source-specific station terms technique to regional and teleseismic distances and adopted the algorithm for probabilistic, nonlinear, global-search location. We evaluated the potential of the method to compute precise relative hypocentre locations on a global scale. The method has been applied to two specific test regions using existing P- and pP-phase picks. The first data set consists of 3103 events along the Chilean margin and the second one comprises 1680 earthquakes in the Tonga-Fiji subduction zone. Pick data were obtained from the GEOFON earthquake bulletin, produced using data from all available, global station networks. A set of timing corrections varying as a function of source position was calculated for each seismic station. In this way, we could correct the systematic errors introduced into the locations by the inaccuracies in the assumed velocity structure without explicitly solving for a velocity model. Residual statistics show that the median absolute deviation of the travel-time residuals is reduced by 40-60 per cent at regional distances, where the velocity anomalies are strong. Moreover, the spread of the travel-time residuals decreased by similar to 20 per cent at teleseismic distances (>28 degrees). Furthermore, strong variations in initial residuals as a function of recording distance are smoothed out in the final residuals. The relocated catalogues exhibit less scattered locations in depth and sharper images of the seismicity associated with the subducting slabs. Comparison with a high-resolution local catalogue reveals that our relocation process significantly improves the hypocentre locations compared to standard locations.
Humankind and their environment need to be protected from the harmful effects of spent nuclear fuel, and therefore disposal in deep geological formations is favoured worldwide. Suitability of potential host rocks is evaluated, among others, by the retention capacity with respect to radionuclides. Safety assessments are based on the quantification of radionuclide migration lengths with numerical simulations as experiments cannot cover the required temporal (1 Ma) and spatial scales (>100 m).
Aim of the present thesis is to assess the migration of uranium, a geochemically complex radionuclide, in the potential host rock Opalinus Clay. Radionuclide migration in clay formations is governed by diffusion due to their low permeability and retarded by sorption. Both processes highly depend on pore water geochemistry and mineralogy that vary between different facies. Diffusion is quantified with the single-component (SC) approach using one diffusion coefficient for all species and the process-based multi-component (MC) option. With this, each species is assigned its own diffusion coefficient and the interaction with the diffuse double layer is taken into account. Sorption is integrated via a bottom-up approach using mechanistic surface complexation models and cation exchange. Therefore, reactive transport simulations are conducted with the geochemical code PHREEQC to quantify uranium migration, i.e. diffusion and sorption, as a function of mineralogical and geochemical heterogeneities on the host rock scale.
Sorption processes are facies dependent. Migration lengths vary between the Opalinus Clay facies by up to 10 m. Thereby, the geochemistry of the pore water, in particular the partial pressure of carbon dioxide (pCO2), is more decisive for the sorption capacity than the amount of clay minerals. Nevertheless, higher clay mineral quantities compensate geochemical variations. Consequently, sorption processes must be quantified as a function of pore water geochemistry in contact with the mineral assemblage.
Uranium diffusion in the Opalinus Clay is facies independent. Speciation is dominated by aqueous ternary complexes of U(VI) with calcium and carbonate. Differences in the migration lengths between SC and MC diffusion are with +/-5 m negligible. Further, the application of the MC approach highly depends on the quality and availability of the underlying data. Therefore, diffusion processes can be adequately quantified with the SC approach using experimentally determined diffusion coefficients.
The hydrogeological system governs pore water geochemistry within the formation rather than the mineralogy. Diffusive exchange with the adjacent aquifers established geochemical gradients over geological time scales that can enhance migration by up to 25 m. Consequently, uranium sorption processes must be quantified following the identified priority: pCO2 > hydrogeology > mineralogy.
The presented research provides a workflow and orientation for other potential disposal sites with similar pore water geochemistry due to the identified mechanisms and dependencies. With a maximum migration length of 70 m, the retention capacity of the Opalinus Clay with respect to uranium is sufficient to fulfill the German legal minimum requirement of a thickness of at least 100 m.
Understanding evolution and ecology of endemic plants is of great importance for conservation of those rare and endangered species. Pairwise comparisons of plant functional traits could be an adequate method to get insights in evolutionary and ecological processes. We examined whether morphological traits representing competitive ability and habitat specificity differ between endemics and common plants. Therefore, we performed pairwise comparison analyses of 9 plant functional traits in 36 congeneric pairs of endemics and their common congeners on the East Mediterranean island of Cyprus, i.e., the first such study conducted on a Mediterranean island. We found that endemic species prefer higher elevations and more extreme habitats. Endemics were smaller and they had smaller flowers than their common congeners. Common species had higher chromosome numbers than endemic ones. Endemic and common species showed no significant differences in canopy height, inflorescence height, leaf length and width, and flowering period. Our study showed that the situation on a large oceanic island does not differ from results in mainland research areas.
BACKGROUND: We evaluated the potential of cholecalciferol as an enhancer of the first-generation anticoagulant coumatetralyl in the Westphalia anticoagulant-resistant strain of the Norway rat (Rattus norvegicus Berkenhout), characterised by the Tyr139Cys polymorphism on the VKOR enzyme. Because today only the most potent, but also most persistent anticoagulant rodenticides of the second generation remain available to control this strain, new rodenticide solutions are required. RESULTS: Feeding trials in the laboratory confirmed a significant level of efficacy, which was corroborated by field trials in the Munsterland resistance area. After frequency and level of resistance were assessed by blood clotting response tests, field trials were conducted with bait containing coumatetralyl at 375 mg kg(-1) and cholecalciferol at 50 mg kg(-1) or 100 mg kg(-1). Control success was 94% when a large rat infestation comprising 42% resistant animals was treated. Another field trial applying the combination to a rat population that had survived a preceding treatment with bromadiolone resulted in a 99.5% control success according to the first census day, but with some increase in rat activity during subsequent census days. CONCLUSION: The combination of coumatetralyl and cholecalciferol is a promising alternative approach to the most potent second-generation anticoagulants in resistance management, particularly in respect of environmental risks, such as secondary poisoning. (C) 2016 Society of Chemical Industry
Flood events can be expressed by a variety of characteristics such as flood magnitude and extent, event duration or incurred loss. Flood estimation and management may benefit from understanding how the different flood characteristics relate to the hydrological catchment conditions preceding the event and to the meteorological conditions throughout the event. In this study, we therefore propose a methodology to investigate the hydro-meteorological controls on different flood characteristics, based on the simulation of the complete flood risk chain from the flood triggering precipitation event, through runoff generation in the catchment, flood routing and possible inundation in the river system and floodplains to flood loss. Conditional cumulative distribution functions and regression tree analysis delineate the seasonal varying flood processes and indicate that the effect of the hydrological pre-conditions, i.e. soil moisture patterns, and of the meteorological conditions, i.e. weather patterns, depends on the considered flood characteristic. The methodology is exemplified for the Elbe catchment. In this catchment, the length of the build-up period, the event duration and the number of gauges undergoing at least a 10-year flood are governed by weather patterns. The affected length and the number of gauges undergoing at least a 2-year flood are however governed by soil moisture patterns. In case of flood severity and loss, the controlling factor is less pronounced. Severity is slightly governed by soil moisture patterns whereas loss is slightly governed by weather patterns. The study highlights that flood magnitude and extent arise from different flood generation processes and concludes that soil moisture patterns as well as weather patterns are not only beneficial to inform on possible flood occurrence but also on the involved flood processes and resulting flood characteristics.
The Arctic is greatly impacted by climate change. The increase in air temperature drives the thawing of permafrost and an increase in coastal erosion and river discharge. This leads to a greater input of sediment and organic matter into coastal waters, which substantially impacts the ecosystems by reducing light transmission through the water column and altering the biogeochemistry, but also the subsistence economy of local people, and changes in climate because of the transformation of organic matter into greenhouse gases. Yet, the quantification of suspended sediment in Arctic coastal and nearshore waters remains unsatisfactory due to the absence of dedicated algorithms to resolve the high loads occurring in the close vicinity of the shoreline. In this study we present the Arctic Nearshore Turbidity Algorithm (ANTA), the first reflectance-turbidity relationship specifically targeted towards Arctic nearshore waters that is tuned with in-situ measurements from the nearshore waters of Herschel Island Qikiqtaruk in the western Canadian Arctic. A semi-empirical model was calibrated for several relevant sensors in ocean color remote sensing, including MODIS, Sentinel 3 (OLCI), Landsat 8 (OLI), and Sentinel 2 (MSI), as well as the older Landsat sensors TM and ETM+. The ANTA performed better with Landsat 8 than with Sentinel 2 and Sentinel 3. The application of the ANTA to Sentinel 2 imagery that matches in-situ turbidity samples taken in Adventfjorden, Svalbard, shows transferability to nearshore areas beyond Herschel Island Qikiqtaruk.
The Arctic is greatly impacted by climate change. The increase in air temperature drives the thawing of permafrost and an increase in coastal erosion and river discharge. This leads to a greater input of sediment and organic matter into coastal waters, which substantially impacts the ecosystems by reducing light transmission through the water column and altering the biogeochemistry, but also the subsistence economy of local people, and changes in climate because of the transformation of organic matter into greenhouse gases. Yet, the quantification of suspended sediment in Arctic coastal and nearshore waters remains unsatisfactory due to the absence of dedicated algorithms to resolve the high loads occurring in the close vicinity of the shoreline. In this study we present the Arctic Nearshore Turbidity Algorithm (ANTA), the first reflectance-turbidity relationship specifically targeted towards Arctic nearshore waters that is tuned with in-situ measurements from the nearshore waters of Herschel Island Qikiqtaruk in the western Canadian Arctic. A semi-empirical model was calibrated for several relevant sensors in ocean color remote sensing, including MODIS, Sentinel 3 (OLCI), Landsat 8 (OLI), and Sentinel 2 (MSI), as well as the older Landsat sensors TM and ETM+. The ANTA performed better with Landsat 8 than with Sentinel 2 and Sentinel 3. The application of the ANTA to Sentinel 2 imagery that matches in-situ turbidity samples taken in Adventfjorden, Svalbard, shows transferability to nearshore areas beyond Herschel Island Qikiqtaruk.
Organic matter deposited in ancient, ice-rich permafrost sediments is vulnerable to climate change and may contribute to the future release of greenhouse gases; it is thus important to get a better characterization of the plant organic matter within such sediments. From a Late Quaternary permafrost sediment core from the Buor Khaya Peninsula, we analysed plant-derived sedimentary ancient DNA (sedaDNA) to identify the taxonomic composition of plant organic matter, and undertook palynological analysis to assess the environmental conditions during deposition. Using sedaDNA, we identified 154 taxa and from pollen and non-pollen palynomorphs we identified 83 taxa. In the deposits dated between 54 and 51 kyr BP, sedaDNA records a diverse low-centred polygon plant community including recurring aquatic pond vegetation while from the pollen record we infer terrestrial open-land vegetation with relatively dry environmental conditions at a regional scale. A fluctuating dominance of either terrestrial or swamp and aquatic taxa in both proxies allowed the local hydrological development of the polygon to be traced. In deposits dated between 11.4 and 9.7 kyr BP (13.4-11.1 cal kyr BP), sedaDNA shows a taxonomic turnover to moist shrub tundra and a lower taxonomic richness compared to the older samples. Pollen also records a shrub tundra community, mostly seen as changes in relative proportions of the most dominant taxa, while a decrease in taxonomic richness was less pronounced compared to sedaDNA. Our results show the advantages of using sedaDNA in combination with palynological analyses when macrofossils are rarely preserved. The high resolution of the sedaDNA record provides a detailed picture of the taxonomic composition of plant-derived organic matter throughout the core, and palynological analyses prove valuable by allowing for inferences of regional environmental conditions.
The large variety of atmospheric circulation systems affecting the eastern Asian climate is reflected by the complex Asian vegetation distribution. Particularly in the transition zones of these circulation systems, vegetation is supposed to be very sensitive to climate change. Since proxy records are scarce, hitherto a mechanistic understanding of the past spatio-temporal climate-vegetation relationship is lacking. To assess the Holocene vegetation change and to obtain an ensemble of potential mid-Holocene biome distributions for eastern Asia, we forced the diagnostic biome model BIOME4 with climate anomalies of different transient Holocene climate simulations performed in coupled atmosphere-ocean(-vegetation) models. The simulated biome changes are compared with pollen-based biome records for different key regions. In all simulations, substantial biome shifts during the last 6000 years are confined to the high northern latitudes and the monsoon-westerly wind transition zone, but the temporal evolution and amplitude of change strongly depend on the climate forcing. Large parts of the southern tundra are replaced by taiga during the mid-Holocene due to a warmer growing season and the boreal treeline in northern Asia is shifted northward by approx. 4 degrees in the ensemble mean, ranging from 1.5 to 6 degrees in the individual simulations, respectively. This simulated treeline shift is in agreement with pollen-based reconstructions from northern Siberia. The desert fraction in the transition zone is reduced by 21% during the mid-Holocene compared to pre-industrial due to enhanced precipitation. The desert-steppe margin is shifted westward by 5 degrees (1-9 degrees in the individual simulations). The forest biomes are expanded north-westward by 2 degrees, ranging from 0 to 4 degrees in the single simulations. These results corroborate pollen-based reconstructions indicating an extended forest area in north-central China during the mid-Holocene. According to the model, the forest-to-non-forest and steppe-to-desert changes in the climate transition zones are spatially not uniform and not linear since the mid-Holocene.
The polar and subtropical jet streams are strong upper-level winds with a crucial influence on weather throughout the Northern Hemisphere midlatitudes. In particular, the polar jet is located between cold arctic air to the north and warmer subtropical air to the south. Strongly meandering states therefore often lead to extreme surface weather. The parameter values of the detection scheme are optimized using simulated annealing and a skill function that accounts for the zonal-mean jet stream position (Rikus, 2015). After the successful optimization process, we apply our scheme to reanalysis data covering 1979-2015 and calculate seasonal-mean probabilistic maps and trends in wind strength and position of jet streams. We present longitudinally defined probability distributions of the positions for both jets for all on the Northern Hemisphere seasons. This shows that winter is characterized by two well-separated jets over Europe and Asia (ca. 20 degrees W to 140 degrees E). In contrast, summer normally has a single merged jet over the western hemisphere but can have both merged and separated jet states in the eastern hemisphere.
Effects of topographic smoothing on the simulation of winter precipitation in High Mountain Asia
(2017)
Numerous studies have projected future changes in High Mountain Asia water resources based on temperature and precipitation from global circulation models (GCMs) under future climate scenarios. Although the potential benefit of such studies is immense, coarse grid-scale GCMs are unable to resolve High Mountain Asia's complex topography and thus have a biased representation of regional weather and climate. This study investigates biases in the simulation of physical mechanisms that generate snowfall and contribute to snowpack in High Mountain Asia in coarse topography experiments using the Weather Research and Forecasting model. Regional snowpack is event driven, thus 33 extreme winter orographic precipitation events are simulated at fine atmospheric resolution with 6.67 km resolution topography and smoothed 1.85° × 1.25° GCM topography. As with many modified topography experiments performed in other regions, the distribution of precipitation is highly dependent on first-order orographic effects, which dominate regional meteorology. However, we demonstrate that topographic smoothing enhances circulation in simulated extratropical cyclones, with significant impacts on orographic precipitation. Despite precipitation reductions of 28% over the highest ranges, due to reduced ascent on windward slopes, total precipitation over the study domain increased by an average of 9% in smoothed topography experiments on account of intensified extratropical cyclone dynamics and cross-barrier moisture flux. These findings identify an important source of bias in coarse-resolution simulated precipitation in High Mountain Asia, with important implications for the application of GCMs toward projecting future hydroclimate in the region.
Postseismic surface deformation associated with great subduction earthquakes is controlled by asthenosphere rheology, frictional properties of the fault, and structural complexity. Here by modeling GPS displacements in the 6 years following the 2010 M-w 8.8 Maule earthquake in Chile, we investigate the impact of heterogeneous viscosity distribution in the South American subcontinental asthenosphere on the 3-D postseismic deformation pattern. The observed postseismic deformation is characterized by flexure of the South America plate with peak uplift in the Andean mountain range and subsidence in the hinterland. We find that, at the time scale of observation, over 2 orders of magnitude gradual increase in asthenosphere viscosity from the arc area toward the cratonic hinterland is needed to jointly explain horizontal and vertical displacements. Our findings present an efficient method to estimate spatial variations of viscosity, which clearly improves the fitting to the vertical signal of deformation. Lateral changes in asthenosphere viscosity can be correlated with the thermomechanical transition from weak subvolcanic arc mantle to strong subcratonic mantle, thus suggesting a stationary heterogeneous viscosity structure. However, we cannot rule out a transient viscosity structure (e.g., power law rheology) with the short time span of observation.
A hydrochemical approach to quantify the role of return flow in a surface flow-dominated catchment
(2017)
Stormflow generation in headwater catchments dominated by subsurface flow has been studied extensively, yet catchments dominated by surface flow have received less attention. We addressed this by testing whether stormflow chemistry is controlled by either (a) the event-water signature of overland flow, or (b) the pre-event water signature of return flow. We used a high-resolution hydrochemical data set of stormflow and end-members of multiple storms in an end-member mixing analysis to determine the number of end-members needed to explain stormflow, characterize and identify potential end-members, calculate their contributions to stormflow, and develop a conceptual model of stormflow. The arrangement and relative positioning of end-members in stormflow mixing space suggest that saturation excess overland flow (26-48%) and return flow from two different subsurface storage pools (17-53%) are both similarly important for stormflow. These results suggest that pipes and fractures are important flow paths to rapidly release stored water and highlight the value of within-event resolution hydrochemical data to assess the full range and dynamics of flow paths.
Avalanche activity is an important factor when estimating the regional avalanche danger. Moreover, a complete and detailed picture of avalanche activity is needed to understand the processes that lead to natural avalanche release. Currently, information on avalanche activity is mainly obtained through visual observations. However, this involves large uncertainties in the number and release times, influencing the subsequent analysis. Therefore, alternative methods for the remote detection of snow avalanches in particular in non-observed areas are highly desirable. In this study, we use the excited ground vibration to identify avalanches automatically. The specific seismic signature of avalanches facilitates the objective detection by a recently developed classification procedure. A probabilistic description of the signals, called hidden Markov models, allows the robust identification of corresponding signals in the continuous data stream. The procedure is based upon learning a general background model from continuous seismic data. Then, a single reference waveform is used to update an event-specific classifier. Thus, a minimum amount of training data is required by constructing such a classifier on the fly. In this study, we processed five days of continuous data recorded in the Swiss Alps during the avalanche winter 1999. With the restriction of testing large wet-snow avalanches only, the presented approach achieved very convincing results. We successfully detect avalanches over a large volume and distance range. Ninety-two percentage of all detections (43 out of 47) could be confirmed as avalanche events; only four false alarms are reported. We see a clear dependence of recognition capability on run-out distance and source-receiver distance of the observed events: Avalanches are detectable up to a source-receiver distance of eight times the avalanche length. Implications for analyzing a more comprehensive data set (smaller events and different flow regimes) are discussed in detail.
This study explores the suitability of a single hillslope as a parsimonious representation of a catchment in a physically based model. We test this hypothesis by picturing two distinctly different catchments in perceptual models and translating these pictures into parametric setups of 2-D physically based hillslope models. The model parametrizations are based on a comprehensive field data set, expert knowledge and process-based reasoning. Evaluation against streamflow data highlights that both models predicted the annual pattern of streamflow generation as well as the hydrographs acceptably. However, a look beyond performance measures revealed deficiencies in streamflow simulations during the summer season and during individual rainfall-runoff events as well as a mismatch between observed and simulated soil water dynamics. Some of these shortcomings can be related to our perception of the systems and to the chosen hydrological model, while others point to limitations of the representative hillslope concept itself. Nevertheless, our results confirm that representative hillslope models are a suitable tool to assess the importance of different data sources as well as to challenge our perception of the dominant hydrological processes we want to represent therein. Consequently, these models are a promising step forward in the search for the optimal representation of catchments in physically based models.
Precambrian microcontinents represent key tectonic units in the accretionary collages of the western Central Asian Orogenic Belt (CAOB), and their geological history is reasonably well established since the Mesoproterozoic but remains weakly constrained for older epochs due to a scarcity of exposed Palaeoproterozoic and Archaean rocks. Early Precambrian rocks were previously reported from several metamorphic complexes in the Kyrgyz Tianshan orogenic belt, mainly based on multigrain conventional zircon dating, but the present study only confirmed such rocks at one site, namely in the Kuilyu Complex of eastern Kyrgyzstan. New single grain SHRIMP II zircon ages, geochemical data, and whole-rock Nd isotopic compositions for granitoid gneisses of the Kuilyu Complex elucidate the age, origin and tectonic settings of this oldest continental fragment in the Tianshan. The Kuilyu Complex is part of the basement in the Ishim - Middle Tianshan microcontinent. It consist of a strongly deformed and metamorphosed supracrustal assemblage of paragneisses and schists which are tectonically interlayered with amphibolites, migmatites and granitoid gneisses. Our zircon dating indicates that the Kuilyu Complex contains two suites of Palaeoproterozoic granitoid gneisses with magmatic protolith ages of ca. 2.32-2.33 Ga and 1.85 Ga. Granitoid magmatism at 1.85 Ga was almost immediately followed by amphibolite-facies metamorphism at ca 1.83 Ga, evidenced by growth of metamorphic zircon rims. The older, ca 2.3 Ga granitoid gneisses chemically correspond to calc-alkaline, metaluminous, I-type magnesian quartz diorite and granodiorite. The protolith of the younger, ca. 1.85 Ga granite-gneiss is an alkalic-calcic, metaluminous to peraluminous, ferroan medium-grained porphyric granite with chemical features resembling A-type granites. The 2.3 Ga and 1.85 Ga granitoid gneisses have slightly to distinctly negative initial epsilon(Nd) values of -1.2 and -6.6, and similar depleted mantle Nd model ages of 2.7-2.6 Ga, which imply melting of Neoarchaean continental crust. The zircon age patterns of the Kuilyu Complex resemble those of exposed rocks in the Tarim Craton, where episodes of granitoid magmatism at ca. 2.3-2.4 and 1.85 Ga, followed by amphibolite-facies metamorphism at ca 1.85 Ga, are also recorded. Similarities in the early Precambrian magmatic and metamorphic episodes as well as similar histories during the Neoproterozoic and early Palaeozoic suggest that the Ishim-Middle Tianshan microcontinent was rifted off the Tarim Craton. Similar age patterns also suggest possible tectonic links of the Kuilyu and Tarim continental blocks with the Baidrag Block of central Mongolia. In contrast, substantial differences in age and Precambrian evolution between the Anrakhai block of southern Kazakhstan and the Kuilyu Complex argue against a previous connection and suggest the former to represent an independent continental terrane. Current data show that early Precambrian rocks in the western CAOB outside Tarim only occur at two sites, namely in the Anrakhai Complex of southern Kazakhstan and in the Kuilyu Complex of eastern Kyrgyzstan. (C) 2016 Elsevier Ltd. All rights reserved.
Through the zmir-Ankara-Erzincan and the Vardar oceans suture zones, convergence between the Eurasian and African plates played a key role in controlling Palaeogene magmatism in north-western Anatolia, northern Aegean, and eastern Balkans. LA-ICP-MS dating of U and Pb isotopes on zircon separates from the tuffs of the Harmankaya Volcanic Rocks, which are inter-fingered with the lower-middle Eocene deposits of the Gazikoy Formation to the north of the Ganos Fault and the Karaaac Formation in the Gelibolu Peninsula, yielded a late Ypresian (51Ma) age. The chemical characteristics suggest that the lavas and tuffs of the Harmankaya Volcanic Rocks are products of syn- or post-collision magmas. These volcanic rocks show also close affinities to the subduction-related magmas. In addition to the already known andesitic volcanic rocks, our field observations in Gokceada Island indicate also the existence of granitic and rhyolitic rocks (Marmaros Magmatic Assemblage). Our U-Pb zircon age data has shown that the newly discovered Marmaros granitic plutons intruded during late Oligocene (26Ma) into the deposits of the Karaaac Formation in Gokceada Island. LA-ICP-MS dating of U and Pb isotopes on zircon separates from the Marmaros rhyolitic rocks yielded a late Oligocene (26Ma) crystallization age. Geochemical characteristics indicate that the more-evolved Oligocene granitic and rhyolitic rock of the Marmaros Magmatic Assemblage possibly assimilated a greater amount of crustal material than the lower Eocene Harmankaya Volcanic Rocks. Geochemical features and age relationships suggest increasing amounts of crustal contamination and a decreasing subduction signature during the evolution of magmas in NW Turkey from the early Eocene to the Oligocene. The magmatic activity developed following the northward subduction of the zmir-Ankara-Erzincan oceanic lithosphere and the earliest Palaeocene final continental collision between the Sakarya and Anatolide-Tauride zones.
The effects of coupling between different layers of the atmosphere during Stratospheric Sudden Warming (SSW) events have been studied quite extensively in the past fewyears, and in this context large lunitidal enhancements in the equatorial ionosphere have also been widely discussed. In this study we report about the longitudinal variabilities in lunitidal enhancement in the equatorial electrojet (EEJ) during SSWs through ground and space observations in the Peruvian and Indian sectors. We observe that the amplification of lunitidal oscillations in EEJ is significantly larger over the Peruvian sector in comparison to the Indian sector. We further compare the lunitidal oscillations in both the sectors during the 2005-2006 and 2008-2009 major SSW events and during a non-SSW winter of 2006-2007. It is found that the lunitidal amplitude in EEJ over the Peruvian sector showed similar enhancements during both the major SSWs, but the enhancements were notably different in the Indian sector. Independent from SSW events, we have also performed a climatological analysis of the lunar modulation of the EEJ during December solstice over both the sectors by using 10years of CHAMP magnetic measurements and found larger lunitidal amplitudes over the Peruvian sector confirming the results from ground magnetometer observations. We have also analyzed the semidiurnal lunar tidal amplitude in neutral temperature measurements from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) at 110km and found lesser longitudinal variability than the lunitidal amplitude in EEJ. Our results suggest that the longitudinal variabilities in lunitidal modulation of the EEJ during SSWs could be related to electrodynamics in the E region dynamo.
The Misho complex in Northwest Iran is a prominent topographic massif bounded by well known active faults. Our new structural analysis of this area indicates that faulting has important role in the exhumation of this complex. The conjugate orientation of the North and South Misho Faults caused uplift in the Misho and exhumation of the Precambrian crystalline basement. Our structural and stratigraphic data shows that rapid uplift could have been initiation since the 21-22 Ma and exhumation rate was about 0.16 to 0.24 km/Ma. To refine this age, we performed U/Pb analysis of detrital zircon from the Upper Red Formation using LA-ICP-MS. We conducted AFT analysis on 6 basement samples from the hanging wall and 1 sample from the Upper Red Formation in the footwall NMF. Uplift in the hanging wall of NMF led to resting of sample 916 marl. This geochronologic and thermochronologic data shows that exhumation in the MC is diachronously along strike and affected by faults. The phase of exhumation is documented in the study area and entire Iranian plateau is related to the final closure of the Neo-Tethys and northward motion of the Arabian Plate.
The crystallization kinetics of silicate liquids were studied experimentally in the system haplogranite-B-Li-H2O, at variable degrees of undercooling and variable water concentration. We investigated the kinetics of nucleation and crystallization of unseeded synthetic hydrous haplogranite with 1 wt % Li2O + 2 center dot 3 wt % B2O3 added (composition C1) and 2 wt % Li2O + 4 center dot 6 wt % B2O3 added (composition C2). Compositions C1 and C2 are simplified representative bulk compositions of Li-rich pegmatites and their highly differentiated cores, respectively. Starting water contents varied between 3 and 9 wt %. With few exceptions, the system remained water-undersaturated. About 86 isothermal runs of 1-60 days duration, grouped in 25 time series of constant temperature and initial H2O content, were carried out at temperatures from 400 to 700A degrees C at 300 MPa, corresponding to variable degrees of undercooling between the liquidus and glass transition. Viscosity measurements indicate that the glass transition for both compositions is below 400A degrees C for 3 wt % water and below 300A degrees C for 6 center dot 5 wt % water. The melts remained virtually crystal free at 400A degrees C, about 100A degrees C and 120A degrees C above the glass transition for compositions C1 and C2, respectively, in experiments up to 30 days long. This result is consistent with the existence of low-temperature, undercooled melts in the crust. At lower values of undercooling the runs crystallized partially, up to about 70% volume fraction. Undercooling and the amount of water are the main factors controlling nucleation and growth rates, and therefore textures. Minerals nucleate and grow sequentially according to mineral-specific nucleation delays. The mineral assemblage started with Li-Al stuffed quartz (in C1) and virgilite (in C2), solid-solutions between quartz and gamma-spodumene. The quartz-like phases were typically followed by spherulitic alkali feldspar-quartz intergrowths, euhedral petalite, and fine-grained muscovite. Nearly pure quartz formed as rims and replacement of metastable virgilite and stuffed quartz, in particular at the boron- and water-rich crystallization front of large feldspar or petalite. With the exception of muscovite, all minerals nucleated heterogeneously, on the capsule wall or on pre-existing minerals, and grew inwards, towards the capsule center. Experimental textures resembled the textures of zoned pegmatites, including skeletal, graphic, unidirectional, radiating, spherulitic, massive, and replacement textures. In some cases, when fluid saturation was reached, miarolitic cavities developed containing euhedral crystals. Although unidirectional growth rates appeared to slow down in time, volumetric rates for stable graphic alkali-feldspar quartz intergrowths and petalite remained constant for up to 60 days and similar to 70% crystallization. Metastable stuffed quartz and virgilite diminished in their growth rates in runs of 30 days or longer, were resorbed in the melt, and were partially replaced by second-generation quartz. Unobstructed, self-sustained crystal growth in conditions of very low nucleation density appears to be the dominant mechanism to form giant pegmatitic crystals, although experimental growth rates are much slower than predicted in nature based on conductive-cooling models.
The early Cretaceous Paraná–Etendeka Large Igneous Province is attributed to the impact of the Tristan mantle plume on the base of the continental lithosphere and the associated opening of the South Atlantic Ocean during the breakup of West Gondwana. Although the geochemistry of the Paraná and Etendeka volcanic rocks has been extensively studied, there is still disagreement on the role of the mantle plume in the production of the magma types observed, because some of their primary compositions are obscured by continental crustal contamination. However, there are related plutonic rocks that preserve mantle signatures. The Doros Complex is a shallow-level mafic intrusion within the Etendeka Province of Namibia. New 39Ar/40Ar step-heating ages for Doros gabbros from this study (weighted mean of 130 ± 1 Ma; 2σ error) confirm contemporaneity with the Paraná–Etendeka magmatic event. The Doros suite yields mean ɛNd values of +5·3 ± 1·0 (1σ; n = 11), initial 87Sr/86Sr = 0·70418 ± 0·00017 (n = 11) and 206Pb/204Pb = 18·11 ± 0·06 (n = 13) at 132 Ma. The clustering of isotopic data and trends in incompatible trace element ratios indicate that all the magmas in the complex were derived from the same mantle source components, during the same melting episode. By quantitative isotopic modelling of mixing processes, we constrain the Doros parental magma to comprise 60–80% melt of a depleted asthenospheric mantle component and 20–40% melt of a more enriched, Tristan plume-derived, asthenospheric component. No lithospheric mantle component is required to explain the Doros magma compositions. The chilled margin to the complex is the only rock type that shows evidence of significant continental crustal contamination, by assimilation of the metasedimentary host-rock upon emplacement. The identification of a substantial Tristan plume component in the Doros source confirms the integral role of the deep-seated thermal anomaly in Paraná–Etendeka magmatism. We show, in addition, that the Doros suite has consistent, strong geochemical affinities with the Tafelkop group ‘ferropicrite’ lavas of the Etendeka Province. This provides crucial evidence in support of Doros as the eruptive site for the Tafelkop lavas, thereby linking the Doros magmatism to the earliest eruptive phase in the Etendeka event. The distinctive chemistry of this magma group has been attributed to relatively deep decompression melting of pyroxenite-bearing material in the heterogeneous Tristan plume head, related to the initial impact of the plume on the base of the lithosphere.
Two nuclear explosions were carried out by the Democratic People’s Republic of North Korea in January and September 2016. Epicenters were located close to those of the 2006, 2009, and 2013 previous explosions. We perform a seismological analysis of the 2016 events combining the analysis of full waveforms at regional distances and seismic array beams at teleseismic distances. We estimate the most relevant source parameters, such as source depth, moment release, and full moment tensor (MT). The best MT solution can be decomposed into an isotropic source, directly related with the explosion and an additional deviatoric term, likely due to near‐source interactions with topographic and/or underground facilities features. We additionally perform an accurate resolution test to assess source parameters uncertainties and trade‐offs. This analysis sheds light on source parameters inconsistencies among studies on previous shallow explosive sources. The resolution of the true MT is hindered by strong source parameters trade‐offs, so that a broad range of well‐fitting MT solutions can be found, spanning from a dominant positive isotropic term to a dominant negative vertical compensated linear vector dipole. The true mechanism can be discriminated by additionally modeling first‐motion polarities at seismic arrays at teleseismic distances. A comparative assessment of the 2016 explosion with earlier nuclear tests documents similar vertical waveforms but a significant increase of amplitude for the 2016 explosions, which proves that the 9 September 2016 was the largest nuclear explosion ever performed in North Korea with a magnitude Mw 4.9 and a shallow depth of less than 2 km, although there are no proofs of a fusion explosion. Modeling transversal component waveforms suggests variable size and orientation of the double‐couple components of the 2009, 2013, and 2016 sources.
The problem of estimating the maximum possible earthquake magnitude m(max) has attracted growing attention in recent years. Due to sparse data, the role of uncertainties becomes crucial. In this work, we determine the uncertainties related to the maximum magnitude in terms of confidence intervals. Using an earthquake catalog of Iran, m(max) is estimated for different predefined levels of confidence in six seismotectonic zones. Assuming the doubly truncated Gutenberg-Richter distribution as a statistical model for earthquake magnitudes, confidence intervals for the maximum possible magnitude of earthquakes are calculated in each zone. While the lower limit of the confidence interval is the magnitude of the maximum observed event, the upper limit is calculated from the catalog and the statistical model. For this aim, we use the original catalog which no declustering methods applied on as well as a declustered version of the catalog. Based on the study by Holschneider et al. (Bull Seismol Soc Am 101(4): 1649-1659, 2011), the confidence interval for m(max) is frequently unbounded, especially if high levels of confidence are required. In this case, no information is gained from the data. Therefore, we elaborate for which settings finite confidence levels are obtained. In this work, Iran is divided into six seismotectonic zones, namely Alborz, Azerbaijan, Zagros, Makran, Kopet Dagh, Central Iran. Although calculations of the confidence interval in Central Iran and Zagros seismotectonic zones are relatively acceptable for meaningful levels of confidence, results in Kopet Dagh, Alborz, Azerbaijan and Makran are not that much promising. The results indicate that estimating mmax from an earthquake catalog for reasonable levels of confidence alone is almost impossible.
Carbon (C) sequestration in soils plays a key role in the global C cycle. It is therefore crucial to adequately monitor dynamics in soil organic carbon (Delta SOC) stocks when aiming to reveal underlying processes and potential drivers. However, small-scale spatial (10-30 m) and temporal changes in SOC stocks, particularly pronounced in arable lands, are hard to assess. The main reasons for this are limitations of the well-established methods. On the one hand, repeated soil inventories, often used in long-term field trials, reveal spatial patterns and trends in Delta SOC but require a longer observation period and a sufficient number of repetitions. On the other hand, eddy covariance measurements of C fluxes towards a complete C budget of the soil-plant-atmosphere system may help to obtain temporal Delta SOC patterns but lack small-scale spatial resolution. To overcome these limitations, this study presents a reliable method to detect both short-term temporal dynamics as well as small-scale spatial differences of Delta SOC using measurements of the net ecosystem carbon balance (NECB) as a proxy. To estimate the NECB, a combination of automatic chamber (AC) measurements of CO2 exchange and empirically modeled aboveground biomass development (NPPshoot / were used. To verify our method, results were compared with Delta SOC observed by soil resampling. Soil resampling and AC measurements were performed from 2010 to 2014 at a colluvial depression located in the hummocky ground moraine landscape of northeastern Germany. The measurement site is characterized by a variable groundwater level (GWL) and pronounced small-scale spatial heterogeneity regarding SOC and nitrogen (Nt) stocks. Tendencies and magnitude of Delta SOC values derived by AC measurements and repeated soil inventories corresponded well. The period of maximum plant growth was identified as being most important for the development of spatial differences in annual Delta SOC. Hence, we were able to confirm that AC-based C budgets are able to reveal small-scale spatial differences and short-term temporal dynamics of Delta SOC.
Successful delivery of the United Nations sustainable development goals and implementation of the Paris Agreement requires technologies that utilize a wide range of minerals in vast quantities. Metal recycling and technological change will contribute to sustaining supply, but mining must continue and grow for the foreseeable future to ensure that such minerals remain available to industry. New links are needed between existing institutional frameworks to oversee responsible sourcing of minerals, trajectories for mineral exploration, environmental practices, and consumer awareness of the effects of consumption. Here we present, through analysis of a comprehensive set of data and demand forecasts, an interdisciplinary perspective on how best to ensure ecologically viable continuity of global mineral supply over the coming decades.
The Limpopo Basin in southern Africa is prone to droughts which affect the livelihood of millions of people in South Africa, Botswana, Zimbabwe and Mozambique. Seasonal drought early warning is thus vital for the whole region. In this study, the predictability of hydrological droughts during the main runoff period from December to May is assessed using statistical approaches. Three methods (multiple linear models, artificial neural networks, random forest regression trees) are compared in terms of their ability to forecast streamflow with up to 12 months of lead time. The following four main findings result from the study. 1. There are stations in the basin at which standardised streamflow is predictable with lead times up to 12 months. The results show high inter-station differences of forecast skill but reach a coefficient of determination as high as 0.73 (cross validated). 2. A large range of potential predictors is considered in this study, comprising well-established climate indices, customised teleconnection indices derived from sea surface temperatures and antecedent streamflow as a proxy of catchment conditions. El Nino and customised indices, representing sea surface temperature in the Atlantic and Indian oceans, prove to be important teleconnection predictors for the region. Antecedent streamflow is a strong predictor in small catchments (with median 42% explained variance), whereas teleconnections exert a stronger influence in large catchments. 3. Multiple linear models show the best forecast skill in this study and the greatest robustness compared to artificial neural networks and random forest regression trees, despite their capabilities to represent nonlinear relationships. 4. Employed in early warning, the models can be used to forecast a specific drought level. Even if the coefficient of determination is low, the forecast models have a skill better than a climatological forecast, which is shown by analysis of receiver operating characteristics (ROCs). Seasonal statistical forecasts in the Limpopo show promising results, and thus it is recommended to employ them as complementary to existing forecasts in order to strengthen preparedness for droughts.
A comprehensive hydrometeorological dataset is presented spanning the period 1 January 201131 December 2014 to improve the understanding of the hydrological processes leading to flash floods and the relation between rainfall, runoff, erosion and sediment transport in a mesoscale catchment (Auzon, 116 km(2)) of the Mediterranean region. Badlands are present in the Auzon catchment and well connected to high-gradient channels of bedrock rivers which promotes the transfer of suspended solids downstream. The number of observed variables, the various sensors involved (both in situ and remote) and the space-time resolution (similar to km(2), similar to min) of this comprehensive dataset make it a unique contribution to research communities focused on hydrometeorology, surface hydrology and erosion. Given that rainfall is highly variable in space and time in this region, the observation system enables assessment of the hydrological response to rainfall fields. Indeed, (i) rainfall data are provided by rain gauges (both a research network of 21 rain gauges with a 5 min time step and an operational network of 10 rain gauges with a 5 min or 1 h time step), S-band Doppler dual-polarization radars (1 km(2), 5 min resolution), disdrometers (16 sensors working at 30 s or 1 min time step) and Micro Rain Radars (5 sensors, 100m height resolution). Additionally, during the special observation period (SOP-1) of the HyMeX (Hydrological Cycle in the Mediterranean Experiment) project, two X-band radars provided precipitation measurements at very fine spatial and temporal scales (1 ha, 5 min). (ii) Other meteorological data are taken from the operational surface weather observation stations of Meteo-France (including 2m air temperature, atmospheric pressure, 2 m relative humidity, 10m wind speed and direction, global radiation) at the hourly time resolution (six stations in the region of interest). (iii) The monitoring of surface hydrology and suspended sediment is multi-scale and based on nested catchments. Three hydrometric stations estimate water discharge at a 2-10 min time resolution. Two of these stations also measure additional physico-chemical variables (turbidity, temperature, conductivity) and water samples are collected automatically during floods, allowing further geochemical characterization of water and suspended solids. Two experimental plots monitor overland flow and erosion at 1 min time resolution on a hillslope with vineyard. A network of 11 sensors installed in the intermittent hydrographic network continuously measures water level and water temperature in headwater subcatchments (from 0.17 to 116 km(2)) at a time resolution of 2-5 min. A network of soil moisture sensors enables the continuous measurement of soil volumetric water content at 20 min time resolution at 9 sites. Additionally, concomitant observations (soil moisture measurements and stream gauging) were performed during floods between 2012 and 2014. Finally, this dataset is considered appropriate for understanding the rainfall variability in time and space at fine scales, improving areal rainfall estimations and progressing in distributed hydrological and erosion modelling.
This habilitation thesis includes seven case studies that examine climate variability during the past 3.5 million years from different temporal and spatial perspectives. The main geographical focus is on the climatic events of the of the African and Asian monsoonal system, the North Atlantic as well as the Arctic Ocean. The results of this study are based on marine and terrestrial climate archives obtained by sedimentological and geochemical methods, and subsequently analyzed by various statistical methods.
The results herein presented results provide a picture of the climatic background conditions of past cold and warm periods, the sensitivity of past climatic climate phases in relation to changes in the atmospheric carbon dioxide content, and the tight linkage between the low and high latitude climate system. Based on the results, it is concluded that a warm background climate state strongly influenced and/or partially reversed the linear relationships between individual climate processes that are valid today. Also, the driving force of the low latitudes for climate variability of the high latitudes is emphasized in the present work, which is contrary to the conventional view that the global climate change of the past 3.5 million years was predominantly controlled by the high latitude climate variability. Furthermore, it is found that on long geologic time scales (>1000 years to millions of years), solar irradiance variability due to changes in the Earth-Sun-Moon System may have increased the sensitivity of low and high latitudes to Influenced changes in atmospheric carbon dioxide.
Taken together, these findings provide new insights into the sensitivity of past climate phases and provide new background conditions for numerical models, that predict future climate change.
Mountain channels can be strongly coupled with adjacent hillslopes, exchanging both mass and energy. However, hypotheses of the underlying cause and effect relations are based on indirect observations that do not resolve the mechanics of channel-hillslope coupling at the process scale. Here we present direct observational data of a coupled channel-hillslope system in the catchment area of the Erlenbach, a mountain stream in Switzerland. A slow-moving landslide flanking this alpine stream failed after a flood had eroded an alluvial step in the channel at its base, representing evidence for an upsystem link in channel-hillslope coupling. Progressive accumulation of landslide debris in the channel resulted in a renewed step, stabilizing the hillslope and restoring the channel step in a downsystem link. Thus, upsystem and downsystem coupling mechanisms are joined in a negative feedback cycle. In this cycle, debuttressing and rebuttressing due to channel bed erosion and alluviation are the dominant controls on hillslope stability. Based on an order of magnitude estimate it is plausible that the observed feedback mechanism is a relevant process in the production of coarse (>2 mm) sediment in the Erlenbach.