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Glacial legacies on interglacial vegetation at the Pliocene-Pleistocene transition in NE Asia
(2016)
Broad-scale climate control of vegetation is widely assumed. Vegetation-climate lags are generally thought to have lasted no more than a few centuries. Here our palaeoecological study challenges this concept over glacial–interglacial timescales. Through multivariate analyses of pollen assemblages from Lake El’gygytgyn, Russian Far East and other data we show that interglacial vegetation during the Plio-Pleistocene transition mainly reflects conditions of the preceding glacial instead of contemporary interglacial climate. Vegetation–climate disequilibrium may persist for several millennia, related to the combined effects of permafrost persistence, distant glacial refugia and fire. In contrast, no effects from the preceding interglacial on glacial vegetation are detected. We propose that disequilibrium was stronger during the Plio-Pleistocene transition than during the Mid-Pliocene Warm Period when, in addition to climate, herbivory was important. By analogy to the past, we suggest today’s widespread larch ecosystem on permafrost is not in climate equilibrium. Vegetation-based reconstructions of interglacial climates used to assess atmospheric CO2–temperature relationships may thus yield misleading simulations of past global climate sensitivity.
In-situ Ar-40/Ar-39 laser ablation dating of white-mica grains was performed on samples from the footwall of a crustal-scale extensional fault (Katschberg Normal Fault; KNF) that accommodated eastward orogen-parallel displacement of Alpine orogenic crust in the eastern part of the Tauern Window. This dating yields predominantly cooling ages ranging from 31 to 13 Myr, with most ages clustering between 21 and 17 Myr. Folded white micas that predate the main Katschberg foliation yield, within error, the same ages as white-mica grains that overgrow this foliation. However, the absolute ages of both generations are older at the base (20 Myr) where their grain size is larger (300-500 mu m), than at the top and adjacent to the hangingwall (17 Myr) of this shear zone where grain size is smaller (<100-300 mu m). This fining-upward trend of white-mica grain size within the KNF is associated with a reduction of the closure temperature from the base (similar to 445 degrees C) to the top (<400 degrees C) and explains the counter-intuitive trend of downward-increasing age of cooling in the footwall. The new data show that rapid cooling within the KNF of the eastern Tauern Window started sometime before 21 Myr according to the Ar-40/Ar-39 white-mica cooling ages and between 25-21 Myr according to the new Rb/Sr white-mica ages, i.e., shortly after the attainment of the thermal peak in the Tauern Window at similar to 25 Myr ago. These new data, combined with literature data, support earlier cooling in the eastern part of then Tauem Window than in the western part by some 3-5 Myr. (C) 2016 Elsevier B.V. All rights reserved.
This review presents a compositional database of primary anatectic granitoid magmas, entirely based on melt inclusions (MI) in high-grade metamorphic rocks. Although MI are well known to igneous petrologists and have been extensively studied in intrusive and extrusive rocks, MI in crustal rocks that have undergone anatexis (migmatites and granulites) are a novel subject of research. They are generally trapped along the heating path by peritectic phases produced by incongruent melting reactions. Primary MI in high-grade metamorphic rocks are small, commonly 5-10 pm in diameter, and their most common mineral host is peritectic garnet. In most cases inclusions have crystallized into a cryptocrystalline aggregate and contain a granitoid phase assemblage (nanogranitoid inclusions) with quartz, K-feldspar, plagioclase, and one or two mica depending on the particular circumstances. After their experimental remelting under high-confining pressure, nanogranitoid MI can be analyzed combining several techniques (EMP, LA-ICP-MS, NanoSIMS, Raman). The trapped melt is granitic and metaluminous to peraluminous, and sometimes granodioritic, tonalitic, and trondhjemitic in composition, in agreement with the different P-T-a(H2o) conditions of melting and protolith composition, and overlap the composition of experimental glasses produced at similar conditions. Being trapped along the up-temperature trajectory as opposed to classic MI in igneous rocks formed during down-temperature magma crystallization fundamental information provided by nanogranitoid MI is the pristine composition of the natural primary anatectic melt for the specific rock under investigation. So far similar to 600 nanogranitoid MI, coming from several occurrences from different geologic and geodynamic settings and ages, have been characterized. Although the compiled MI database should be expanded to other potential sources of crustal magmas, MI data collected so far can be already used as natural "starting-point" compositions to track the processes involved in formation and evolution of granitoid magmas.
Grazing by domestic ungulates can have substantial impacts on forests in arid and semi-arid regions, possibly including severe loss of carbon from the soil. Predicting net livestock impacts on soil organic carbon stocks remains challenging, however, due to the dependence on animal loads and on soil and environmental parameters. The objective of this study was to better understand grazing effects on soil organic carbon in seasonal tropical dry forests of north-eastern Brazil (Caatinga) by quantifying carbon stocks of the upper soil profile (0–5 cm depth) and greater soil depths (>5 cm depth down to bedrock) along a gradient of grazing intensity while accounting for other influencing factors such as soil texture, vegetation, landscape topography, and water availability. We analysed soil organic carbon, soil clay content, altitude above sea level, soil depth to bedrock, distance to the nearest permanent water body, species diversity of perennial plants and aboveground biomass on 45 study plots located in the vicinity of the Itaparica Reservoir, Pernambuco, Brazil. Livestock (mainly goats and cattle) are unevenly distributed in the studied ecosystem, thus grazing intensity was accounted for based on the weight of livestock droppings per square metre and classified as no or light, intermediate, or heavy grazing. The mean soil organic carbon in the area was 16.86 ± 1.28 Mg ha−1 C with approximately one-quarter found in the upper 5 cm of the soil profile (4.14 ± 0.43 Mg ha−1 C) and the remainder (12.57 ± 0.97 Mg ha−1 C) in greater soil depths (>5 cm). Heavy grazing led to significantly lower soil organic carbon stocks in the upper 5 cm, whereas no effect on soil organic carbon of the soil overall or in greater soil depths was detectable. The soil’s clay content and the altitude proved to be the most relevant factors influencing overall soil organic carbon stocks and those in greater soil depths (>5 cm). Our findings suggest that grazing causes substantial release of carbon from Brazilian dry forest soils, which should be addressed through improved grazing management via a legally compulsory rotation system. This would ultimately contribute to the conservation of a unique forest system and associated ecosystem services.
Solute concentration variability is of fundamental importance for the chemical and ecological state of streams. It is often closely related to discharge variability and can be characterized in terms of a solute export regime. Previous studies, especially in lowland catchments, report that nitrate is often exported with an accretion pattern of increasing concentrations with increasing discharge. Several modeling approaches exist to predict the export regime of solutes from the spatial relationship of discharge generating zones with solute availability in the catchment. For a small agriculturally managed lowland catchment in central Germany, we show that this relationship is controlled by the depth to groundwater table and its temporal dynamics. Principal component analysis of groundwater level time series from wells distributed throughout the catchment allowed derivation of a representative groundwater level time series that explained most of the discharge variability. Groundwater sampling revealed consistently decreasing nitrate concentrations with an increasing thickness of the unsaturated zone. The relationships of depth to groundwater table to discharge and to nitrate concentration were parameterized and integrated to successfully model catchment discharge and nitrate export on the basis of groundwater level variations alone. This study shows that intensive and uniform agricultural land use likely results in a clear and consistent concentration-depth relationship of nitrate, which can be utilized in simple approaches to predict stream nitrate export dynamics at the catchment scale. (C) 2016 Elsevier Ltd. All rights reserved.
Tectonic blocks and slabs of mafic-ultramafic rocks are distributed discontinuously in the Yuli metamorphic belt of Taiwan. The blocks include rare omphacite metagabbros and gamet-epidote blueschists in the Wanjung and Juisui (Tamayen) areas, respectively. Such high-pressure (HP) mineral assemblages have been attributed to a mid-Miocene subduction event. However, the surrounding psammitic, pelitic and chloritic schists are the dominant greenschist-facies lithologies of the Yuli belt. In the Chinshuichi area, tectonic blocks are enclosed in garnet-bearing metapelites, suggesting elevated pressures. In this area, we recently discovered meta-plagiogranite containing the assemblage glaucophane + omphacite (X-Jd up to 039) + rutile + quartz, indicating P-T conditions near 13 kbar/550 degrees C. New equilibrium phase modeling of a garnet-paragonite mica schist and compositional isopleths for peak assemblage minerals garnet and phengite (Si = 3.33-3.37 pfu) indicate metamorphic conditions of 15.5-17 kbar/530-550 degrees C. These P-T estimates are higher than previously reported in the Yuli belt and suggest that both tectonic blocks and host metapelites underwent HP metamorphism. The juxtaposition of tectonic blocks and metapelites apparently occurred during the formation of a subduction-accretionary complex, followed by exhumation facilitated by a collisional event. These new findings imply that HP metamorphism was not limited to tectonic blocks, and instead played a significant role attending orogenesis in eastern Taiwan. (C) 2015 Elsevier B.V. All rights reserved.
Understanding the role of natural climate variability under the pressure of human induced changes of climate and landscapes, is crucial to improve future projections and adaption strategies. This doctoral thesis aims to reconstruct Holocene climate and environmental changes in NE Germany based on annually laminated lake sediments. The work contributes to the ICLEA project (Integrated CLimate and Landscape Evolution Analyses). ICLEA intends to compare multiple high-resolution proxy records with independent chronologies from the N central European lowlands, in order to disentangle the impact of climate change and human land use on landscape development during the Lateglacial and Holocene. In this respect, two study sites in NE Germany are investigated in this doctoral project, Lake Tiefer See and palaeolake Wukenfurche. While both sediment records are studied with a combination of high-resolution sediment microfacies and geochemical analyses (e.g. µ-XRF, carbon geochemistry and stable isotopes), detailed proxy understanding mainly focused on the continuous 7.7 m long sediment core from Lake Tiefer See covering the last ~6000 years. Three main objectives are pursued at Lake Tiefer See: (1) to perform a reliable and independent chronology, (2) to establish microfacies and geochemical proxies as indicators for climate and environmental changes, and (3) to trace the effects of climate variability and human activity on sediment deposition.
Addressing the first aim, a reliable chronology of Lake Tiefer See is compiled by using a multiple-dating concept. Varve counting and tephra findings form the chronological framework for the last ~6000 years. The good agreement with independent radiocarbon dates of terrestrial plant remains verifies the robustness of the age model. The resulting reliable and independent chronology of Lake Tiefer See and, additionally, the identification of nine tephras provide a valuable base for detailed comparison and synchronization of the Lake Tiefer See data set with other climate records. The sediment profile of Lake Tiefer See exhibits striking alternations between well-varved and non-varved sediment intervals. The combination of microfacies, geochemical and microfossil (i.e. Cladocera and diatom) analyses indicates that these changes of varve preservation are caused by variations of lake circulation in Lake Tiefer See. An exception is the well-varved sediment deposited since AD 1924, which is mainly influenced by human-induced lake eutrophication. Well-varved intervals before the 20th century are considered to reflect phases of reduced lake circulation and, consequently, stronger anoxic conditions. Instead, non-varved intervals indicate increased lake circulation in Lake Tiefer See, leading to more oxygenated conditions at the lake ground. Furthermore, lake circulation is not only influencing sediment deposition, but also geochemical processes in the lake. As, for example, the proxy meaning of δ13COM varies in time in response to changes of the oxygen regime in the lake hypolinion. During reduced lake circulation and stronger anoxic conditions δ13COM is influenced by microbial carbon cycling. In contrast, organic matter degradation controls δ13COM during phases of intensified lake circulation and more oxygenated conditions. The varve preservation indicates an increasing trend of lake circulation at Lake Tiefer See after ~4000 cal a BP. This trend is superimposed by decadal to centennial scale variability of lake circulation intensity. Comparison to other records in Central Europe suggests that the long-term trend is probably related to gradual changes in Northern Hemisphere orbital forcing, which induced colder and windier conditions in Central Europe and, therefore, reinforced lake circulation. Decadal to centennial scale periods of increased lake circulation coincide with settlement phases at Lake Tiefer See, as inferred from pollen data of the same sediment record. Deforestation reduced the wind shelter of the lake, which probably increased the sensitivity of lake circulation to wind stress. However, results of this thesis also suggest that several of these phases of increased lake circulation are additionally reinforced by climate changes. A first indication is provided by the comparison to the Baltic Sea record, which shows striking correspondence between major non-varved intervals at Lake Tiefer See and bioturbated sediments in the Baltic Sea. Furthermore, a preliminary comparison to the ICLEA study site Lake Czechowskie (N central Poland) shows a coincidence of at least three phases of increased lake circulation in both lakes, which concur with periods of known climate changes (2.8 ka event, ’Migration Period’ and ’Little Ice Age’). These results suggest an additional over-regional climate forcing also on short term increased of lake circulation in Lake Tiefer See.
In summary, the results of this thesis suggest that lake circulation at Lake Tiefer See is driven by a combination of long-term and short-term climate changes as well as of anthropogenic deforestation phases. Furthermore, the lake circulation drives geochemical cycles in the lake affecting the meaning of proxy data. Therefore, the work presented here expands the knowledge of climate and environmental variability in NE Germany. Furthermore, the integration of the Lake Tiefer See multi-proxy record in a regional comparison with another ICLEA side, Lake Czechowskie, enabled to better decipher climate changes and human impact on the lake system. These first results suggest a huge potential for further detailed regional comparisons to better understand palaeoclimate dynamics in N central Europe.
Ice-wedge polygon (IWP) peatlands in the Arctic and Subarctic are extremely vulnerable to climatic and environmental change. We present the results of a multidisciplinary paleoenvironmental study on IWPs in the northern Yukon, Canada. High-resolution laboratory analyses were carried out on a permafrost core and the overlying seasonally thawed (active) layer, from an IWP located in a drained lake basin on Herschel Island. In relation to 14 Accelerator Mass Spectrometry (AMS) radiocarbon dates spanning the last 5000 years, we report sedimentary data including grain size distribution and biogeochemical parameters (organic carbon, nitrogen, C/N ratio, delta C-13), stable water isotopes (delta O-18, delta D), as well as fossil pollen, plant macrofossil and diatom assemblages. Three sediment units (SUS) correspond to the main stages of deposition (1) in a thermokarst lake (SW : 4950 to 3950 cal yrs BP), (2) during transition from lacustrine to palustrine conditions after lake drainage (SU2: 3950 to 3120 cal yrs BP), and (3) in palustrine conditions of the IWP field that developed after drainage (SU3: 3120 cal yrs BP to 2012 CE). The lacustrine phase (pre 3950 cal yrs BP) is characterized by planktonic-benthic and pioneer diatom species indicating circumneutral waters, and very few plant macrofossils. The pollen record has captured a regional signal of relatively stable vegetation composition and climate for the lacustrine stage of the record until 3950 cal yrs BP. Palustrine conditions with benthic and acidophilic diatom species characterize the peaty shallow-water environments of the low-centered IWP. The transition from lacustrine to palustrine conditions was accompanied by acidification and rapid revegetation of the lake bottom within about 100 years. Since the palustrine phase we consider the pollen record as a local vegetation proxy dominated by the plant communities growing in the IWP. Ice-wedge cracking in water-saturated sediments started immediately after lake drainage at about 3950 cal yrs BP and led to the formation of an IWP mire. Permafrost aggradation through downward closed-system freezing of the lake talik is indicated by the stable water isotope record. The originally submerged IWP center underwent gradual drying during the past 2000 years. This study highlights the sensitivity of permafrost landscapes to climate and environmental change throughout the Holocene. (C) 2016 Elsevier Ltd. All rights reserved.
The southernmost thrust of the Himalayan orogenic wedge that separates the foreland from the orogen, the Main Frontal Thrust, is thought to accommodate most of the ongoing crustal shortening in the Sub-Himalaya. Steepened longitudinal river profile segments, terrace offsets, and back-tilted fluvial terraces within the Kangra reentrant of the NW Sub-Himalaya suggest Holocene activity of the Jwalamukhi Thrust (JMT) and other thrust faults that may be associated with strain partitioning along the toe of the Himalayan wedge. To assess the shortening accommodated by the JMT, we combine morphometric terrain analyses with in situ Be-10-based surface-exposure dating of the deformed terraces. Incision into upper Pleistocene sediments within the Kangra Basin created two late Pleistocene terrace levels (T1 and T2). Subsequent early Holocene aggradation shortly before similar to 10ka was followed by episodic reincision, which created four cut-and-fill terrace levels, the oldest of which (T3) was formed at 10.10.9ka. A vertical offset of 445m of terrace T3 across the JMT indicates a shortening rate of 5.60.8 to 7.51.1mma(-1) over the last similar to 10ka. This result suggests that thrusting along the JMT accommodates 40-60% of the total Sub-Himalayan shortening in the Kangra reentrant over the Holocene. We speculate that this out-of-sequence shortening may have been triggered or at least enhanced by late Pleistocene and Holocene erosion of sediments from the Kangra Basin.
The lakes in the Kenyan Rift Valley offer the unique opportunity to study a wide range of hydrochemical environmental conditions, ranging from freshwater to highly saline and alkaline lakes. Because little is known about the hydro- and biogeochemical conditions in the underlying lake sediments, it was the aim of this study to extend the already existing data sets with data from porewater and biomarker analyses. Additionally, reduced sulphur compounds and sulphate reduction rates in the sediment were determined. The new data was used to examine the anthropogenic and microbial influence on the lakes sediments as well as the influence of the water chemistry on the degradation and preservation of organic matter in the sediment column. The lakes discussed in this study are: Logipi, Eight (a small crater lake in the region of Kangirinyang), Baringo, Bogoria, Naivasha, Oloiden, and Sonachi.
The biomarker compositions were similar in all studied lake sediments; nevertheless, there were some differences between the saline and freshwater lakes. One of those differences is the occurrence of a molecule related to β-carotene, which was only found in the saline lakes. This molecule most likely originates from cyanobacteria, single-celled organisms which are commonly found in saline lakes. In the two freshwater lakes, stigmasterol, a sterol characteristic for freshwater algae, was found. In this study, it was shown that Lakes Bogoria and Sonachi can be used for environmental reconstructions with biomarkers, because the absence of oxygen at the lake bottoms slowed the degradation process. Other lakes, like for example Lake Naivasha, cannot be used for such reconstructions, because of the large anthropogenic influence. But the biomarkers proved to be a useful tool to study those anthropogenic influences. Additionally, it was observed that horizons with a high concentration of elemental sulphur can be used as temporal markers. Those horizons were deposited during times when the lake levels were very low. The sulphur was deposited by microorganisms which are capable of anoxygenic photosynthesis or sulphide oxidation.
The new sediment record from the deep Dead Sea basin (ICDP core 5017-1) provides a unique archive for hydroclimatic variability in the Levant. Here, we present high-resolution sediment facies analysis and elemental composition by micro-X-ray fluorescence (mu XRF) scanning of core 5017-1 to trace lake levels and responses of the regional hydroclimatology during the time interval from ca. 117 to 75 ka, i. e. the transition between the last interglacial and the onset of the last glaciation. We distinguished six major micro-facies types and interpreted these and their alterations in the core in terms of relative lake level changes. The two end-member facies for highest and lowest lake levels are (a) up to several metres thick, greenish sediments of alternating aragonite and detrital marl laminae (aad) and (b) thick halite facies, respectively. Intermediate lake levels are characterised by detrital marls with varying amounts of aragonite, gypsum or halite, reflecting lower-amplitude, shorter-term variability. Two intervals of pronounced lake level drops occurred at similar to 110-108 +/- 5 and similar to 93-87 +/- 7 ka. They likely coincide with stadial conditions in the central Mediterranean (Melisey I and II pollen zones in Monticchio) and low global sea levels during Marine Isotope Stage (MIS) 5d and 5b. However, our data do not support the current hypothesis of an almost complete desiccation of the Dead Sea during the earlier of these lake level low stands based on a recovered gravel layer. Based on new petrographic analyses, we propose that, although it was a low stand, this well-sorted gravel layer may be a vestige of a thick turbidite that has been washed out during drilling rather than an in situ beach deposit. Two intervals of higher lake stands at similar to 108-93 +/- 6 and similar to 87-75 +/- 7 ka correspond to interstadial conditions in the central Mediterranean, i. e. pollen zones St. Germain I and II in Monticchio, and Greenland interstadials (GI) 24+23 and 21 in Greenland, as well as to sapropels S4 and S3 in the Mediterranean Sea. These apparent correlations suggest a close link of the climate in the Levant to North Atlantic and Mediterranean climates during the time of the build-up of Northern Hemisphere ice shields in the early last glacial period.
Subsurface microbial communities undertake many terminal electron-accepting processes, often simultaneously. Using a tritium-based assay, we measured the potential hydrogen oxidation catalyzed by hydrogenase enzymes in several subsurface sedimentary environments (Lake Van, Barents Sea, Equatorial Pacific, and Gulf of Mexico) with different predominant electron-acceptors. Hydrogenases constitute a diverse family of enzymes expressed by microorganisms that utilize molecular hydrogen as a metabolic substrate, product, or intermediate. The assay reveals the potential for utilizing molecular hydrogen and allows qualitative detection of microbial activity irrespective of the predominant electron-accepting process. Because the method only requires samples frozen immediately after recovery, the assay can be used for identifying microbial activity in subsurface ecosystems without the need to preserve live material. We measured potential hydrogen oxidation rates in all samples from multiple depths at several sites that collectively span a wide range of environmental conditions and biogeochemical zones. Potential activity normalized to total cell abundance ranges over five orders of magnitude and varies, dependent upon the predominant terminal electron acceptor. Lowest per-cell potential rates characterize the zone of nitrate reduction and highest per-cell potential rates occur in the methanogenic zone. Possible reasons for this relationship to predominant electron acceptor include (i) increasing importance of fermentation in successively deeper biogeochemical zones and (ii) adaptation of H(2)ases to successively higher concentrations of H-2 in successively deeper zones.
Subsurface microbial communities undertake many terminal electron-accepting processes, often simultaneously. Using a tritium-based assay, we measured the potential hydrogen oxidation catalyzed by hydrogenase enzymes in several subsurface sedimentary environments (Lake Van, Barents Sea, Equatorial Pacific, and Gulf of Mexico) with different predominant electron-acceptors. Hydrogenases constitute a diverse family of enzymes expressed by microorganisms that utilize molecular hydrogen as a metabolic substrate, product, or intermediate. The assay reveals the potential for utilizing molecular hydrogen and allows qualitative detection of microbial activity irrespective of the predominant electron-accepting process. Because the method only requires samples frozen immediately after recovery, the assay can be used for identifying microbial activity in subsurface ecosystems without the need to preserve live material. We measured potential hydrogen oxidation rates in all samples from multiple depths at several sites that collectively span a wide range of environmental conditions and biogeochemical zones. Potential activity normalized to total cell abundance ranges over five orders of magnitude and varies, dependent upon the predominant terminal electron acceptor. Lowest per-cell potential rates characterize the zone of nitrate reduction and highest per-cell potential rates occur in the methanogenic zone. Possible reasons for this relationship to predominant electron acceptor include (i) increasing importance of fermentation in successively deeper biogeochemical zones and (ii) adaptation of H(2)ases to successively higher concentrations of H-2 in successively deeper zones.
Hydrological and climatological controls on radiocarbon concentrations in a tropical stalagmite
(2016)
Precisely-dated stalagmites are increasingly important archives for the reconstruction of terrestrial paleoclimate at very high temporal resolution. In-depth understanding of local conditions at the cave site and of the processes driving stalagmite deposition is of paramount importance for interpreting proxy signals incorporated in stalagmite carbonate. Here we present a sub-decadally resolved dead carbon fraction (DCF) record for a stalagmite from Yok Balum Cave (southern Belize). The record is coupled to parallel stable carbon isotope (delta C-13) and U/Ca measurements, as well as radiocarbon (C-14) measurements from soils overlying the cave system. Using a karst carbon cycle model we disentangle the importance of soil and karst processes on stalagmite DCF incorporation, revealing a dominant host rock dissolution control on total DCF. Covariation between DCF, delta C-13, and U/Ca indicates that karst processes are a common driver of all three parameters, suggesting possible use of delta C-13 and trace element ratios to independently quantify DCF variability. A statistically significant multi-decadal lag of variable length exists between DCF and reconstructed solar activity, suggesting that solar activity influenced regional precipitation in Mesoamerica over the past 1500 years, but that the relationship was non-static. Although the precise nature of the observed lag is unclear, solar-induced changes in North Atlantic oceanic and atmospheric dynamics may play a role. (C) 2016 Elsevier Ltd. All rights reserved.
We analyze the spatiotemporal distribution of fault geometries from seismicity induced by fluid injection at The Geysers geothermal field. The consistency of these faults with the local stress field is investigated using (1) the fault instability coefficient I comparing the orientation of a fault with the optimal orientation for failure in the assumed stress field and (2) the misfit angle beta between slip vectors observed from focal mechanisms and predicted from stress tensor. A statistical approach is applied to calculate the most likely fault instabilities considering the uncertainties from focal mechanisms and stress inversion. We find that faults activated by fluid injection may display a broad range in orientations. About 72% of the analyzed seismicity occurs on faults with favorable orientation for failure with respect to the stress field. However, a number of events are observed either to occur on severely misoriented faults or to slip in a different orientation than predicted from stress field. These events mostly occur during periods of high injection rates and are located in proximity to the injection wells. From the stress inversion, the friction coefficient providing the largest overall instability is mu = 0.5. About 91% of the events are activated with an estimated excess pore pressure <10 MPa, in agreement with previous models considering the combined effect of thermal and poroelastic stress changes from fluid injection. Furthermore, high seismic activity and largest magnitudes occur on favorably oriented faults with large instability coefficients and low slip misfit angles.
Ongoing climate change is known to cause an increase in the frequency and amplitude of local temperature and precipitation extremes in many regions of the Earth. While gradual changes in the climatological conditions have already been shown to strongly influence plant flowering dates, the question arises if and how extremes specifically impact the timing of this important phenological phase. Studying this question calls for the application of statistical methods that are tailored to the specific properties of event time series. Here, we employ event coincidence analysis, a novel statistical tool that allows assessing whether or not two types of events exhibit similar sequences of occurrences in order to systematically quantify simultaneities between meteorological extremes and the timing of the flowering of four shrub species across Germany. Our study confirms previous findings of experimental studies by highlighting the impact of early spring temperatures on the flowering of the investigated plants. However, previous studies solely based on correlation analysis do not allow deriving explicit estimates of the strength of such interdependencies without further assumptions, a gap that is closed by our analysis. In addition to direct impacts of extremely warm and cold spring temperatures, our analysis reveals statistically significant indications of an influence of temperature extremes in the autumn preceding the flowering.
The Cenozoic East African Rift System (EARS) is an exceptional example of active continental extension, providing opportunities for furthering our understanding of hydrocarbon plays within rifts. It is divided into structurally distinct western and eastern branches. The western branch comprises deep rift basins separated by transfer zones, commonly localised onto pre-existing structures, offering good regional scale hydrocarbon traps. At a basin-scale, local discrete inherited structures might also play an important role on fault localisation and hydrocarbon distribution. Here, we consider the evolution of the Central basin of the Malawi Rift, in particular the influence of pre-existing structural fabrics. Integrating basin-scale multichannel 2D, and high resolution seismic datasets we constrain the border, Mlowe-Nkhata, fault system (MNF) to the west of the basin and smaller Mbamba fault (MF) to the east and document their evolution. Intra basin structures define a series of horsts, which initiated as convergent transfers, along the basin axis. The horsts are offset along a NE SW striking transfer fault parallel to and along strike of the onshore Karoo (Permo-Triassic) Ruhuhu graben. Discrete pre-existing structures probably determined its location and, oriented obliquely to the extension orientation it accommodated predominantly strike-slip deformation, with more slowly accrued dip-slip. To the north of this transfer fault, the overall basin architecture is asymmetric, thickening to the west throughout; while to the south, an initially symmetric graben architecture became increasingly asymmetric in sediment distribution as strain localised onto the western MNF. The presence of the axial horst increasingly focussed sediment supply to the west. As the transfer fault increased its displacement, so this axial supply was interrupted, effectively starving the south-east while ponding sediments between the western horst margin and the transfer fault. This asymmetric bathymetry and partitioned sedimentation continues to the present-day, overprinting the early basin symmetry and configuration. Sediments deposited earlier become increasingly dissected and fault juxtapositions changed at a small (10-100 m) scale. The observed influence of basin-scale transfer faults on sediment dispersal and fault compartmentalization due to pre-existing structures oblique to the extension orientation is relevant to analogous exploration settings. (C) 2016 Elsevier Ltd. All rights reserved.
Synergistic applications based on integrated hyperspectral and lidar data are receiving a growing interest from the remote-sensing community. A prerequisite for the optimum sensor fusion of hyperspectral and lidar data is an accurate geometric coalignment. The simple unadjusted integration of lidar elevation and hyperspectral reflectance causes a substantial loss of information and does not exploit the full potential of both sensors. This paper presents a novel approach for the geometric coalignment of hyperspectral and lidar airborne data, based on their respective adopted return intensity information. The complete approach incorporates ray tracing and subpixel procedures in order to overcome grid inherent discretization. It aims at the correction of extrinsic and intrinsic (camera resectioning) parameters of the hyperspectral sensor. In additional to a tie-point-based coregistration, we introduce a ray-tracing-based back projection of the lidar intensities for area-based cost aggregation. The approach consists of three processing steps. First is a coarse automatic tie-point-based boresight alignment. The second step coregisters the hyperspectral data to the lidar intensities. Third is a parametric coalignment refinement with an area-based cost aggregation. This hybrid approach of combining tie-point features and area-based cost aggregation methods for the parametric coregistration of hyperspectral intensity values to their corresponding lidar intensities results in a root-mean-square error of 1/3 pixel. It indicates that a highly integrated and stringent combination of different coalignment methods leads to an improvement of the multisensor coregistration.
We review recent progress in studying structural properties of liquids using X-ray absorption spectroscopy coupled with the Paris-Edinburgh press at third-generation synchrotron facilities. This experimental method allows for detecting subtle changes in atomic arrangements of melts over a wide pressure-temperature range. It has been also employed to monitor variations of the local coordination environment of diluted species contained in glasses, liquids and crystalline phases as a function of the pressure and temperature. Such information is of great importance for gaining deeper insights into the physico-chemical properties of liquids at extreme condition, including the understanding of such phenomena as liquid-liquid phase transitions, viscosity drops and various transport properties of geological melts. Here, we describe the experimental approach and discuss its potential in structural characterization on selected scientific highlights. Finally, the current ongoing instrumental developments and future scientific opportunities are discussed.
The Pamirs represent the indented westward continuation of the northern margin of the Tibetan Plateau, dividing the Tarim and Tajik basins. Their evolution may be a key factor influencing aridification of the Asian interior, yet the tectonics of the Pamir Salient are poorly understood. We present a provenance study of the Aertashi section, a Paleogene to late Neogene clastic succession deposited in the Tarim basin to the north of the NW margin of Tibet (the West Kunlun) and to the east of the Pamirs. Our detrital zircon U-Pb ages coupled with zircon fission track, bulk rock Sm-Nd, and petrography data document changes in contributing source terranes during the Oligocene to Miocene, which can be correlated to regional tectonics. We propose a model for the evolution of the Pamir and West Kunlun (WKL), in which the WKL formed topography since at least similar to 200 Ma. By similar to 25 Ma, movement along the Pamir-bounding faults such as the Kashgar-Yecheng Transfer System had commenced, marking the onset of Pamir indentation into the Tarim-Tajik basin. This is coincident with basinward expansion of the northern WKL margin, which changed the palaeodrainage pattern within the Kunlun, progressively cutting off the more southerly WKL sources from the Tarim basin. An abrupt change in the provenance and facies of sediments at Aertashi has a maximum age of 14 Ma; this change records when the Pamir indenter had propagated sufficiently far north that the North Pamir was now located proximal to the Aertashi region.
The common carp (Cyprinus carpio) is a highly invasive species and an ecological engineer. It has been repeatedly shown to increase nutrient concentrations and phytoplankton biomass while destroying submerged macrophytes, although there are few studies from the Mediterranean region. We studied its impact on the zooplankton community in Laguna de Medina lake, a shallow lake in Jerez de la Frontera, south-west Spain. Carp were removed with rotenone in 2007 but returned in 2010-2011. We compared zooplankton sampled monthly from 8 points from May to December in 2008 (without carp) and 2012 (with carp). Extensive macrophyte beds present in 2008 were absent in 2012. As expected, chlorophyll-a concentrations, turbidity, total suspended solids and total phosphorus were much higher in 2012. Zooplankton richness decreased from 21 taxa in 2008 to 8 taxa in 2012, accompanied by a decrease in Shannon-Wiener diversity, an increase in Evenness and a change in size distribution with loss of larger taxa. In 2008, the crustaceans were dominated by the macrocladocerans Daphnia magna and Moina brachiata and the large calanoid copepod Arctodiaptomus salinus. In 2012, these three taxa were completely absent and the zooplankton was dominated by the alien cyclopoid Acanthocyclops americanus and the rotifers Brachionus plicatilis and Keratella quadrata. Our results confirm the disappearance of macrocladocera reported by others in mesocosm experiments with carp, and suggest that alien carp facilitate the spread of the alien copepod A. americanus.
The aim of the present study was to investigate nutritional and metabolic parameters during the dry and early postpartum periods of ovulatory and anovulatory cows, as well as their postpartum reproductive performance. Blood samples from 20 multiparous Holstein cows were collected once a week from the far-off dry period to 3 weeks postpartum. Early postpartum (0-3 weeks) ovulation was confirmed using plasma progesterone concentration profiles, and cows were considered ovulatory if they had resumed luteal activity by this point (n = 9), whereas cows that had not were considered anovulatory (n = 11). Data from the ovulatory and anovulatory cows were analyzed separately for the far-off dry period (7-4 weeks prepartum), the close-up dry period (3-1 weeks prepartum), and the early postpartum period (0-3 weeks). Serum gamma-glutamyl transpeptidase activity (far-off, P = 0.065; close-up, P = 0.051; and early postpartum, P = 0.030) and aspartate aminotransferase (close-up, P = 0.050 and early postpartum, P = 0.087) activities were higher in anovulatory than in ovulatory cows. The days open period was longer (P = 0.019) in anovulatory than in ovulatory cows, and the number of artificial inseminations per conception (P = 0.025) was greater. In conclusion, we found that continuously high gamma-glutamyl transpeptidase activities in serum, which may be induced by liver disorders, prevent subsequent ovulation and affect subsequent fertility, even if cows obtain sufficient ovulation-related energy and beta-carotene.
Carbon fiber based felt materials are widely used as gas diffusion layer (GDL) in fuel cells. Their transport properties can be adjusted by adding hydrophobic agents such as polytetrafluoroethylene (PTFE). We present a synchrotron X-ray tomographic study on the felt material Freudenberg H2315 with different PIPE finishing. In this study, we analyze changes in microstructure and shape of GDLs at increasing degree of compression which are related to their specific PTFE load. A dedicated compression device mimicking the channel-land pattern of the flowfield is used to reproduce the inhomogeneous compression found in a fuel cell. Transport relevant geometrical parameters such as porosity, pore size distribution and geometric tortuosity are calculated and consequences for media transport discussed. PTFE finishing results in a marked change of shape of compressed GDLs: surface is smoothed and the invasion of GDL fibers into the flow field channel strongly mitigated. Furthermore, the PTFE impacts the microstructure of the compressed GDL. The number of available wide transport paths is significantly increased as compared to the untreated material. These changes improve the transport capacity liquid water through the GDL and promote the discharge of liquid water droplets from the cell. (C) 2016 Elsevier B.V. All rights reserved.
The effect of methods of statistical downscaling of daily precipitation on changes in extreme flow indices under a plausible future climate change scenario was investigated in 11 catchments selected from 9 countries in different parts of Europe. The catchments vary from 67 to 6171 km(2) in size and cover different climate zones. 15 regional climate model outputs and 8 different statistical downscaling methods, which are broadly categorized as change factor and bias correction based methods, were used for the comparative analyses. Different hydrological models were implemented in different catchments to simulate daily runoff. A set of flood indices were derived from daily flows and their changes have been evaluated by comparing their values derived from simulations corresponding to the current and future climate. Most of the implemented downscaling methods project an increase in the extreme flow indices in most of the catchments. The catchments where the extremes are expected to increase have a rainfall dominated flood regime. In these catchments, the downscaling methods also project an increase in the extreme precipitation in the seasons when the extreme flows occur. In catchments where the flooding is mainly caused by spring/summer snowmelt, the downscaling methods project a decrease in the extreme flows in three of the four catchments considered. A major portion of the variability in the projected changes in the extreme flow indices is attributable to the variability of the climate model ensemble, although the statistical downscaling methods contribute 35-60% of the total variance. (C) 2016 Elsevier B.V. All rights reserved.
Precision horticulture encompasses site- or tree-specific management in fruit plantations. Of decisive importance is spatially resolved data (this means data from each tree) from the production site, since it may enable customized and, therefore, resource-efficient production measures.
The present thesis involves an examination of the apparent electrical conductivity of the soil (ECa), the plant water status spatially measured by means of the crop water stress index (CWSI), and the fruit quality (e.g. fruit size) for Prunus domestica L. (plums) and Citrus x aurantium, Syn. Citrus paradisi (grapefruit). The goals of the present work were i) characterization of the 3D distribution of the apparent electrical conductivity of the soil and variability of the plant’s water status; ii) investigation of the interaction between ECa, CWSI, and fruit quality; and iii) an approach for delineating management zones with respect to managing trees individually.
To that end, the main investigations took place in the plum orchard. This plantation got a slope of 3° grade on Pleistocene and post-Pleistocene substrates in a semi-humid climate (Potsdam, Germany) and encloses an area of 0.37 ha with 156 trees of the cultivar ˈTophit Plusˈ on a Wavit rootstock. The plantation was laid in 2009 with annual and biannual trees spaced 4 m distance along the irrigation system and 5 m between the rows. The trees were watered three times a week with a drip irrigation system positioned 50 cm above ground level providing 1.6 l per tree per event. With the help of geoelectric measurements, the apparent electrical conductivity of the upper soil (0.25 m) was measured for each tree with an electrode spacing of 0.5 m (4-point light hp). In this manner, the plantation was spatially charted with respect to the soil’s ECa. Additionally, tomography measurements were performed for 3D mapping of the soil ECa and spot checks of drilled cores with a profile of up to 1 m. The vegetative, generative, and fruit quality data were collected for each tree. The instantaneous plant water status was comprehensively determined in spot checks with the established Scholander method for water potential analysis (Scholander pressure bomb) as well as thermal imaging. An infrared camera was used for the thermal imaging (ThermaCam SC 500), mounted on a tractor 3.3 m above ground level. The thermal images (320 x 240 px) of the canopy surface were taken with an aperture of 45° and a geometric resolution of 8.54 x 6.41 mm. With the aid of the canopy temperature readings from the thermal images, cross-checked with manual temperature measurements of a dry and a wet reference leaf, the crop water stress index (CWSI) was calculated. Adjustments in CWSI for measurements in a semi-humid climate were developed, whereas the collection of reference temperatures was automatically collected from thermal images.
The bonitur data were transformed with the help of a variance stabilization process into a normal distribution. The statistical analyses as well as the automatic evaluation routine were performed with several scripts in MATLAB® (R2010b and R2016a) and a free program (spatialtoolbox). The hot spot analysis served to check whether an observed pattern is statistically significant. The method was evaluated with an established k-mean analysis. To test the hot-spot analysis by comparison, data from a grapefruit plantation (Adana, Turkey) was collected, including soil ECa, trunk circumference, and yield data. The plantation had 179 trees on a soil of type Xerofkuvent with clay and clay-loamy texture. The examination of the interaction between the critical values from the soil and plant water status information and the vegetative and generative plant growth variables was performed with the application from ANOVA.
The study indicates that the variability of the soil and plant information in fruit production is high, even considering small orchards. It was further indicated that the spatial patterns found in the soil ECa stayed constant through the years (r = 0.88 in 2011-2012 and r = 0.71 in 2012-2013). It was also demonstrated that CWSI determination may also be possible in semi-humid climate. A correlation (r = - 0.65, p < 0.0001) with the established method of leaf water potential analysis was found. The interaction between the ECa from various depths and the plant variables produced a highly significant connection with the topsoil in which the irrigation system was to be found. A correlation between yield and ECatopsoil of r = 0.52 was determined. By using the hot-spot analysis, extreme values in the spatial data could be determined. These extremes served to divide the zones (cold-spot, random, hot-spot). The random zone showed the highest correlation to the plant variables.
In summary it may be said that the cumulative water use efficiency (WUEc) was enhanced with high crop load. While the CWSI had no effect on fruit quality, the interaction of CWSI and WUEc even outweighed the impact of soil ECa on fruit quality in the production system with irrigation. In the plum orchard, irrigation was relevant for obtaining high quality produce even in the semi-humid climate.
Hummocky soil landscapes are characterized by 3D spatial patterns of soil types that result from erosion-affected pedogenesis. Due to tillage and water erosion, truncated profiles have been formed at steep and mid slopes and colluvial soils at hollows, while intact profiles remained at plateau positions. Pedogenetic variations in soil horizons lead to spatial differences in the soil water balance at hillslope positions. Here, possible interactions between erosion affected soil properties, the water balances, and the crop growth and feedback effects of erosion on the leaching rates were assumed. The hypothesis was tested by water balance simulations comparing uniform with hillslope position-specific crop and root growths for soils at plateau, flat mid slope, steep slope, and hollow using the Hydrus-1D program. The boundary condition data were monitored at the CarboZALF-D experimental field site, which was cropped with perennial lucerne (Medicago sativa L.) in 2013 and 2014. Crop and root growth at the four hillslope positions was assumed proportional to observed leaf area index (LAI). Fluxes of dissolved organic and inorganic carbon (DOC, DIC) were obtained from simulated water fluxes and measured DOC and DIC concentrations. For the colluvic soil at hollow, the crop growth was initially highest and later limited by an increasing water table; here the predominately upward flow led to a net input in DIC and DOC. For the truncated soils at steep slopes, simulations support the hypothesis that reduced crop growth caused an increase in percolation and DIC leaching from the subsoil horizons, which in turn led to accelerated soil development and more soil variations along eroding hillslopes in arable soil landscapes. (C) 2015 Elsevier B.V. All rights reserved.
The humid tropics are the region with the highest rate of land-cover change worldwide. Especially prevalent is the deforestation of old-growth tropical forests to create space for cattle pastures and soybean fields.
The regional water cycle is influenced by vegetation cover in various ways. Especially evapotranspiration considerably contributes to water vapor content in the lower atmosphere. Besides active transpiration by plants, evaporation from wetted plant surfaces further known as interception loss is an important supply of water vapor. Changes in interception loss due to change in land cover and the related consequences on the regional water cycle in the humid tropics of Latin America are the research focus of my thesis. (1) In an experimental setup I assess differences in interception loss between an old-growth tropical forest and a soybean plantation. (2) In a modeling study, I examine interception losses of these two vegetation types compared to a younger secondary forest with the use of the Gash interception model, including an uncertainty analysis for the estimation of the necessary model parameters. (3) Studying the water balance of a 192-km² catchment I disentangle the influences of changes in land cover and climatic factors on interception loss.
The three different research sites in my thesis represent a currently typical spectrum for land-cover changes in Latin America. In the first example I study the consequences of deforestation of transitional forest, which forms the transition from the Brazilian tree savanna (cerrado) to tropical rain forest, for the establishment of soybean fields in the southern Amazon basin. The second study site is a young secondary forest within the “Agua Salud” project area in Panama as an example of reforestation of former pastures. The third study site is the Cirí Grande river catchment which comprises a mixture of young and old forests as well as pastures, which is typical for the southern sub-catchments of the Panama Canal.
The experimental approach consists of the indirect estimation of interception loss by measuring throughfall and stem flow. For the first experimental study I measured throughfall as well as stem flow manually. Measurements of the leaf area index of the two land covers do not show distinct differences; hence it could not serve as an explanation for the differences in the measured interception loss. The considerably higher interception loss at the soybean field is attributed to a possible underestimation of stemflow but also to the stronger ventilation within the well-structured plant rows causing higher evaporation rates. This situation is valid only for two months of the rainy season, when soybean plants are fully developed. In the annual balance evapotranspiration at the soybean site is clearly less than at the forest site, accelerating the development of fast runoff components and consequently discharge. In the medium term, a reduction of water availability in the study area can be expected.
For the modeling study, throughfall in a young secondary forest is sampled automatically. The resulting temporally high-resolution dataset allows the distinction between different precipitation and interception events. The core of this study is the sensitivity and uncertainty analysis of the Gash interception model parameters and the consequences for its results. Canopy storage capacity plays a key role for the model and parameter uncertainty. With increasing storage capacity uncertainty in parameter delineation also increases. Evaporation rate as the driving component of the interception process incorporates in this context the largest parameter uncertainty. Depending on the selected method for parameter estimation, parameter values may vary tremendously.
In the third study, I analyze the influence of interception loss on the water balance of the Cirí Grande catchment, incorporating the interlinked effects of temperature, precipitation and changes of the land use mosaic using the SWAT (soil water assessment tool) model. Constructing several land-cover scenarios I assess their influence on the catchment’s discharge. The results show that land-cover change exerts only a small influence on annual discharge in the Cirí Grande catchment whereas an increase in temperature markedly influences evapotranspiration. The temperature-induced larger transpiration and interception loss balances the simultaneous increase in annual precipitation, such that the resulting changes in annual discharge are negligible.
The results of the three studies show the considerable effect of land cover on interception. However, the magnitude of this effect can be masked by changes in local conditions, especially by an increase in temperature. Hence, the results cannot be transferred easily between the different study sites. For modeling purposes, this means that measurements of vegetation characteristics as well as interception loss at the respective sites are indispensable.
Intermontane valley fills
(2016)
Sedimentary valley fills are a widespread characteristic of mountain belts around the world. They transiently store material over time spans ranging from thousands to millions of years and therefore play an important role in modulating the sediment flux from the orogen to the foreland and to oceanic depocenters. In most cases, their formation can be attributed to specific fluvial conditions, which are closely related to climatic and tectonic processes. Hence, valley-fill deposits constitute valuable archives that offer fundamental insight into landscape evolution, and their study may help to assess the impact of future climate change on sediment dynamics.
In this thesis I analyzed intermontane valley-fill deposits to constrain different aspects of the climatic and tectonic history of mountain belts over multiple timescales. First, I developed a method to estimate the thickness distribution of valley fills using artificial neural networks (ANNs). Based on the assumption of geometrical similarity between exposed and buried parts of the landscape, this novel and highly automated technique allows reconstructing fill thickness and bedrock topography on the scale of catchments to entire mountain belts.
Second, I used the new method for estimating the spatial distribution of post-glacial sediments that are stored in the entire European Alps. A comparison with data from exploratory drillings and from geophysical surveys revealed that the model reproduces the measurements with a root mean squared error (RMSE) of 70m and a coefficient of determination (R2) of 0.81. I used the derived sediment thickness estimates in combination with a model of the Last Glacial Maximum (LGM) icecap to infer the lithospheric response to deglaciation, erosion and deposition, and deduce their relative contribution to the present-day rock-uplift rate. For a range of different lithospheric and upper mantle-material properties, the results suggest that the long-wavelength uplift signal can be explained by glacial isostatic adjustment with a small erosional contribution and a substantial but localized tectonic component exceeding 50% in parts of the Eastern Alps and in the Swiss Rhône Valley. Furthermore, this study reveals the particular importance of deconvolving the potential components of rock uplift when interpreting recent movements along active orogens and how this can be used to constrain physical properties of the Earth’s interior.
In a third study, I used the ANN approach to estimate the sediment thickness of alluviated reaches of the Yarlung Tsangpo River, upstream of the rapidly uplifting Namche Barwa massif. This allowed my colleagues and me to reconstruct the ancient river profile of the Yarlung Tsangpo, and to show that in the past, the river had already been deeply incised into the eastern margin of the Tibetan Plateau. Dating of basal sediments from drill cores that reached the paleo-river bed to 2–2.5 Ma are consistent with mineral cooling ages from the Namche Barwa massif, which indicate initiation of rapid uplift at ~4 Ma. Hence, formation of the Tsangpo gorge and aggradation of the voluminous valley fill was most probably a consequence of rapid uplift of the Namche Barwa massif and thus tectonic activity.
The fourth and last study focuses on the interaction of fluvial and glacial processes at the southeastern edge of the Karakoram. Paleo-ice-extent indicators and remnants of a more than 400-m-thick fluvio-lacustrine valley fill point to blockage of the Shyok River, a main tributary of the upper Indus, by the Siachen Glacier, which is the largest glacier in the Karakoram Range. Field observations and 10Be exposure dating attest to a period of recurring lake formation and outburst flooding during the penultimate glaciation prior to ~110 ka. The interaction of Rivers and Glaciers all along the Karakorum is considered a key factor in landscape evolution and presumably promoted headward erosion of the Indus-Shyok drainage system into the western margin of the Tibetan Plateau.
The results of this thesis highlight the strong influence of glaciation and tectonics on valley-fill formation and how this has affected the evolution of different mountain belts. In the Alps valley-fill deposition influenced the magnitude and pattern of rock uplift since ice retreat approximately 17,000 years ago. Conversely, the analyzed valley fills in the Himalaya are much older and reflect environmental conditions that prevailed at ~110 ka and ~2.5 Ma, respectively. Thus, the newly developed method has proven useful for inferring the role of sedimentary valley-fill deposits in landscape evolution on timescales ranging from 1,000 to 10,000,000 years.
The main scope of the InterPACIFIC (Intercomparison of methods for site parameter and velocity profile characterization) project is to assess the reliability of in-hole and surface-wave methods, used for estimating shear wave velocity. Three test-sites with different subsurface conditions were chosen: a soft soil, a stiff soil and a rock outcrop. This paper reports the surface-wave methods results. Specifically 14 teams of expert users analysed the same experimental surface-wave datasets, consisting of both passive and active data. Each team adopted their own strategy to retrieve the dispersion curve and the shear-wave velocity profile at each site. Despite different approaches, the dispersion curves are quite in agreement with each other. Conversely, the shear-wave velocity profiles show a certain variability that increases in correspondence of major stratigraphic interfaces. This larger variability is mainly due to non-uniqueness of the solution and lateral variability. As expected, the observed variability in V-s,V-30 estimatesis small, as solution non-uniqueness plays a limited role. (C) 2015 Elsevier Ltd. All rights reserved.
Zircon (ZrSiO4), hafnon (HfSiO4) and five intermediate compositions were synthesized from a Pb silicate melt. The resulting crystals were 20-300 mu m in size and displayed sector and growth zoning. Raman spectra were acquired at locations in the sample for which preceding electron microprobe (EMP) analyses revealed sufficient compositional homogeneity. The dataset documents shifts of Raman bands with changing composition. In this study, bands that have previously not been reported were found for the intermediate compositions and for pure hafnon, in particular at wavenumbers less than 200 cm(-1). For these external modes, the dataset provides new insight into the compositional dependence of their frequencies. Density-functional theory calculations support the observations and are used for a detailed interpretation of the spectra. The pitfalls of the EMP analysis along the zircon-hafnon join are highlighted.
Coastal fens like the nature reserve "Hutelmoor und Heiligensee" (north-eastern Germany) are important landscape elements along the southern Baltic coast, which exchange fresh water and brackish water with the Baltic Sea. These exchange processes can be understood as experiments with a natural tracer, which may be used to investigate the hydrologic behaviour of these fen systems. With the establishment of coastal protection measures such as dunes and dikes, the installation of surface drainage and, more recently, also nature conservation measures, the hydrologic regime of these coastal wetlands has constantly altered over the last centuries.The rehabilitated wetland "Hutelnnoor und Heiligensee" is suitable for an analysis of hydrologic change as it has been monitored over the time period since nature conservation measures started in the 1990s. Collected data sets included observation of groundwater levels and electrical conductivities, weather data as well as discharge at the outlet of the drainage catchment. In this article, as a second part of the dual publication, processes and quantified process magnitudes have been identified that govern the salt balance of the study area including its variability in space and time. It was detected that - over the period of rehabilitation - salt water entered the catchment with an episodic storm surge by wave overtopping of dunes in 1995. The intruded brackish water was then diluted, which was a slow process extending over decades. It was governed by local groundwater recharge from precipitation and the inflow of relatively fresh groundwater from the hinterland. It is concluded that salt inputs from the Baltic Sea provide a natural tracer of hydrological processes, which can be readily monitored via electrical conductivity measurements.
A unique assemblage including kumdykolite and kokchetavite, polymorphs of albite and K-feldspar, respectively, together with cristobalite, micas, and calcite has been identified in high-pressure granulites of the Orlica-Snieznik dome (Bohemian Massif) as the product of partial melt crystallization in preserved nanogranites. Previous reports of both kumdykolite and kokchetavite in natural rocks are mainly from samples that passed through the diamond stability field. However, because the maximum pressure recorded in these host rocks is <3 GPa, our observations indicate that high pressure is not required for the formation of kumdykolite and kokchetavite, and their presence is not therefore an indicator of ultrahigh-pressure conditions. Detailed microstructural and microchemical investigation of these inclusions indicates that such phases should instead be regarded as (1) a direct mineralogical criteria to identify former melt inclusions with preserved original compositions, including H2O and CO2 contents and (2) indicators of rapid cooling of the host rocks. Thus, the present study provides novel criteria for the interpretation of melt inclusions in natural rocks and allows a more rigorous characterization of partial melts during deep subduction to mantle depth as well as their behavior on exhumation.
Fluvial fill terraces preserve sedimentary archives of landscape responses to climate change, typically over millennial timescales. In the Humahuaca Basin of NW Argentina (Eastern Cordillera, southern Central Andes), our 29 new optically stimulated luminescence ages of late Pleistocene fill terrace sediments demonstrate that the timing of past river aggradation occurred over different intervals on the western and eastern sides of the valley, despite their similar bedrock lithology, mean slopes, and precipitation. In the west, aggradation coincided with periods of increasing precipitation, while in the east, aggradation coincided with decreasing precipitation or more variable conditions. Erosion rates and grain size dependencies in our cosmogenic Be-10 analyses of modern and fill terrace sediments reveal an increased importance of landsliding compared to today on the west side during aggradation, but of similar importance during aggradation on the east side. Differences in the timing of aggradation and the Be-10 data likely result from differences in valley geometry, which causes sediment to be temporarily stored in perched basins on the east side. It appears as if periods of increasing precipitation triggered landslides throughout the region, which induced aggradation in the west, but blockage of the narrow bedrock gorges downstream from the perched basins in the east. As such, basin geometry and fluvial connectivity appear to strongly influence the timing of sediment movement through the system. For larger basins that integrate subbasins with differing geometries or degrees of connectivity (like Humahuaca), sedimentary responses to climate forcing are likely attenuated.
Experience has shown that river floods can significantly hamper the reliability of railway networks and cause extensive structural damage and disruption. As a result, the national railway operator in Austria had to cope with financial losses of more than EUR 100 million due to flooding in recent years. Comprehensive information on potential flood risk hot spots as well as on expected flood damage in Austria is therefore needed for strategic flood risk management. In view of this, the flood damage model RAIL (RAilway Infrastructure Loss) was applied to estimate (1) the expected structural flood damage and (2) the resulting repair costs of railway infrastructure due to a 30-, 100- and 300-year flood in the Austrian Mur River catchment. The results were then used to calculate the expected annual damage of the railway subnetwork and subsequently analysed in terms of their sensitivity to key model assumptions. Additionally, the impact of risk aversion on the estimates was investigated, and the overall results were briefly discussed against the background of climate change and possibly resulting changes in flood risk. The findings indicate that the RAIL model is capable of supporting decision-making in risk management by providing comprehensive risk information on the catchment level. It is furthermore demonstrated that an increased risk aversion of the railway operator has a marked influence on flood damage estimates for the study area and, hence, should be considered with regard to the development of risk management strategies.
Numerous (meta-)gabbroic dikes or stocks occur within the latest Neoproterozoic-early Cambrian series of the Menderes Massif (Anatolide-Tauride Block, western Turkey). These well-preserved rocks were locally converted into eclogitic metagabbros and garnet amphibolites along the contacts or shear zones. Both bulk-rock composition and compositions of igneous clinopyroxenes suggest continental tholeiitic affinity. U-Pb dating of igneous zircons from gabbroic rocks yielded a mean age of 563 +/- 1 Ma (2 sigma), indicating emplacement during the latest Neoproterozoic (Ediacaran). On the other hand, rims of zircons from eclogitic metagabbro gave 535 +/- 3 Ma (2 sigma) (early Cambrian), in addition to 558 +/- 3 Ma (2 sigma) obtained from the igneous core of zircons. These ages are interpreted as the time of high-P metamorphism and crystallization age of gabbroic protolith, respectively. Given the estimated paleogeographic position of the Anatolide-Tauride Block during the late Neoproterozoic and early Cambrian, this orogenic event can be spatially and temporally related to the northward continuity of 600-500 Ma orogenic event (Malagasy/Kuunga orogeny) extending from western margin of India, Madagascar, via Arabia up to northern margin of Gondwana beneath thick Phanerozoic cover series in Arabian Peninsula. Therefore, the high-P evolution of the basement of the Menderes Massif and associated basic intrusions can be interpreted to mark the latest stages of consumption of the basin/oceanic branches and final amalgamation of the Gondwana during the late Neoproterozoic-early Cambrian around the Arabian region. (C) 2015 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
Late Quaternary paleoenvironmental records from the Chatanika River valley near Fairbanks (Alaska)
(2016)
Perennially-frozen deposits are considered as excellent paleoenvironmental archives similar to lacustrine, deep marine, and glacier records because of the long-term and good preservation of fossil records under stable permafrost conditions. A permafrost tunnel in the Vault Creek Valley (Chatanika River Valley, near Fairbanks) exposes a sequence of frozen deposits and ground ice that provides a comprehensive set of proxies to reconstruct the late Quaternary environmental history of Interior Alaska. The multi-proxy approach includes different dating techniques (radiocarbon-accelerator mass spectrometry [AMS C-14], optically stimulated luminescence [OSL], thorium/uranium radioisotope disequilibria [Th-230/U]), as well as methods of sedimentology, paleoecology, hydrochemistry, and stable isotope geochemistry of ground ice. The studied sequence consists of 36-m-thick late Quaternary deposits above schistose bedrock. Main portions of the sequence accumulated during the early and middle Wisconsin periods. The lowermost unit A consists of about 9-m-thick ice-bonded fluvial gravels with sand and peat lenses. A late Sangamon (MIS 5a) age of unit A is assumed. Spruce forest with birch, larch, and some shrubby alder dominated the vegetation. High presence of Sphagnum spores and Cyperaceae pollen points to mires in the Vault Creek Valley. The overlying unit B consists of 10-m-thick alternating fluvial gravels, loess-like silt, and sand layers, penetrated by small ice wedges. OSL dates support a stadial early Wisconsin (MIS 4) age of unit B. Pollen and plant macrofossil data point to spruce forests with some birch interspersed with wetlands around the site. The following unit C is composed of 15-m-thick ice-rich loess-like and organic-rich silt with fossil bones and large ice wedges. Unit C formed during the interstadial mid-Wisconsin (MIS 3) and stadial late Wisconsin (MIS 2) as indicated by radiocarbon ages. Post-depositional slope processes significantly deformed both, ground ice and sediments of unit C. Pollen data show that spruce forests and wetlands dominated the area. The macrofossil remains of Picea, Larix, and Alnus incana ssp. tenuifolia also prove the existence of boreal coniferous forests during the mid-Wisconsin interstadial, which were replaced by treeless tundra-steppe vegetation during the late Wisconsin stadial. Unit C is discordantly overlain by the 2-m-thick late Holocene deposits of unit D. The pollen record of unit D indicates boreal forest vegetation similar to the modern one. The permafrost record from the Vault Creek tunnel reflects more than 90 ka of periglacial landscape dynamics triggered by fluvial and eolian accumulation, and formation of ice-wedge polygons and post depositional deformation by slope processes. The record represents a typical Wisconsin valley-bottom facies in Central Alaska. (C) 2016 Elsevier Ltd. All rights reserved.
Although the climate development over the Holocene in the Northern Hemisphere is well known, palaeolimnological climate reconstructions reveal spatiotemporal variability in northern Eurasia. Here we present a multi-proxy study from north-eastern Siberia combining sediment geochemistry, and diatom and pollen data from lake-sediment cores covering the last 38,000 cal. years. Our results show major changes in pyrite content and fragilarioid diatom species distributions, indicating prolonged seasonal lake-ice cover between similar to 13,500 and similar to 8900 cal. years BP and possibly during the 8200 cal. years BP cold event. A pollen-based climate reconstruction generated a mean July temperature of 17.8 degrees C during the Holocene Thermal Maximum (HTM) between similar to 8900 and similar to 4500 cal. years BP. Naviculoid diatoms appear in the late Holocene indicating a shortening of the seasonal ice cover that continues today. Our results reveal a strong correlation between the applied terrestrial and aquatic indicators and natural seasonal climate dynamics in the Holocene. Planktonic diatoms show a strong response to changes in the lake ecosystem due to recent climate warming in the Anthropocene. We assess other palaeolimnological studies to infer the spatiotemporal pattern of the HTM and affirm that the timing of its onset, a difference of up to 3000 years from north to south, can be well explained by climatic teleconnections. The westerlies brought cold air to this part of Siberia until the Laurentide ice sheet vanished 7000 years ago. The apparent delayed ending of the HTM in the central Siberian record can be ascribed to the exceedance of ecological thresholds trailing behind increases in winter temperatures and decreases in contrast in insolation between seasons during the mid to late Holocene as well as lacking differentiation between summer and winter trends in paleolimnological reconstructions. (C) 2015 Elsevier Ltd. All rights reserved.
Knowledge about the magnitude of localised flooding of riverine areas is crucial for appropriate land management and administration at regional and local levels. However, detection and delineation of localised flooding with remote sensing techniques are often hampered on floodplains by the presence of herbaceous vegetation. To address this problem, this study presents the application of full waveform airborne laser scanning (ALS) data for detection of floodwater extent. In general, water surfaces are characterised by low values of backscattered energy due to water absorption of the infrared laser shots, but the exact strength of the recorded laser pulse depends on the area covered by the targets located within a laser pulse footprint area. To account for this we analysed the physical quantity of radio metrically calibrated ALS data, the backscattering coefficient, in relation to water and vegetation coverage within a single laser footprint. The results showed that the backscatter was negatively correlated to water coverage, and that of the three distinguished classes of water coverage (low, medium, and high) only the class with the largest extent of water cover (>70%) had relatively distinct characteristics that can be used for classification of water surfaces. Following the laser footprint analysis, three classifiers, namely AdaBoost with Decision Tree, Naive Bayes and Random Forest, were utilised to classify laser points into flooded and non-flooded classes and to derive the map of flooding extent. The performance of the classifiers is highly dependent on the set of laser points features used. Best performance was achieved by combining radiometric and geometric laser point features. The accuracy of flooding maps based solely on radiometric features resulted in overall accuracies of up to 70% and was limited due to the overlap of the backscattering coefficient values between water and other land cover classes. Our point-based classification methods assure a high mapping accuracy (similar to 89%) and demonstrate the potential of using full-waveform ALS data to detect water surfaces on floodplain areas with limited water surface exposition through the vegetation canopy. (C) 2016 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS). Published by Elsevier B.V. All rights reserved.
Observed recent and expected future increases in frequency and intensity of climatic extremes in central Europe may pose critical challenges for domestic tree species. Continuous dendrometer recordings provide a valuable source of information on tree stem radius variations, offering the possibility to study a tree's response to environmental influences at a high temporal resolution. In this study, we analyze stem radius variations (SRV) of three domestic tree species (beech, oak, and pine) from 2012 to 2014. We use the novel statistical approach of event coincidence analysis (ECA) to investigate the simultaneous occurrence of extreme daily weather conditions and extreme SRVs, where extremes are defined with respect to the common values at a given phase of the annual growth period. Besides defining extreme events based on individual meteorological variables, we additionally introduce conditional and joint ECA as new multivariate extensions of the original methodology and apply them for testing 105 different combinations of variables regarding their impact on SRV extremes. Our results reveal a strong susceptibility of all three species to the extremes of several meteorological variables. Yet, the inter-species differences regarding their response to the meteorological extremes are comparatively low. The obtained results provide a thorough extension of previous correlation-based studies by emphasizing on the timings of climatic extremes only. We suggest that the employed methodological approach should be further promoted in forest research regarding the investigation of tree responses to changing environmental conditions.
Observed recent and expected future increases in frequency and intensity of climatic extremes in central Europe may pose critical challenges for domestic tree species. Continuous dendrometer recordings provide a valuable source of information on tree stem radius variations, offering the possibility to study a tree's response to environmental influences at a high temporal resolution. In this study, we analyze stem radius variations (SRV) of three domestic tree species (beech, oak, and pine) from 2012 to 2014. We use the novel statistical approach of event coincidence analysis (ECA) to investigate the simultaneous occurrence of extreme daily weather conditions and extreme SRVs, where extremes are defined with respect to the common values at a given phase of the annual growth period. Besides defining extreme events based on individual meteorological variables, we additionally introduce conditional and joint ECA as new multivariate extensions of the original methodology and apply them for testing 105 different combinations of variables regarding their impact on SRV extremes. Our results reveal a strong susceptibility of all three species to the extremes of several meteorological variables. Yet, the inter-species differences regarding their response to the meteorological extremes are comparatively low. The obtained results provide a thorough extension of previous correlation-based studies by emphasizing on the timings of climatic extremes only. We suggest that the employed methodological approach should be further promoted in forest research regarding the investigation of tree responses to changing environmental conditions.
The increase in atmospheric methane concentration, which is determined by an imbalance between its sources and sinks, has led to investigations of the methane cycle in various environments. Aquatic environments are of an exceptional interest due to their active involvement in methane cycling worldwide and in particular in areas sensitive to climate change. Furthermore, being connected with each other aquatic environments form networks that can be spread on vast areas involving marine, freshwater and terrestrial ecosystems. Thus, aquatic systems have a high potential to translate local or regional environmental and subsequently ecosystem changes to a bigger scale. Many studies neglect this connectivity and focus on individual aquatic or terrestrial ecosystems.
The current study focuses on environmental controls of the distribution and aerobic oxidation of methane at the example of two aquatic ecosystems. These ecosystems are Arctic fresh water bodies and the Elbe estuary which represent interfaces between freshwater-terrestrial and freshwater-marine environments, respectively.
Arctic water bodies are significant atmospheric sources of methane. At the same time the methane cycle in Arctic water bodies is strongly affected by the surrounding permafrost environment, which is characterized by high amounts of organic carbon. The results of this thesis indicate that the methane concentrations in Arctic lakes and streams substantially vary between each other being regulated by local landscape features (e.g. floodplain area) and the morphology of the water bodies (lakes, streams and river). The highest methane concentrations were detected in the lake outlets and in a floodplain lake complex. In contrast, the methane concentrations measured at different sites of the Lena River did not vary substantially. The lake complexes in comparison to the Lena River, thus, appear as more individual and heterogeneous systems with a pronounced imprint of the surrounding soil environment. Furthermore, connected with each other Arctic aquatic environments have a large potential to transport methane from methane-rich water bodies such as streams and floodplain lakes to aquatic environments relatively poor in methane such as the Lena River.
Estuaries represent hot spots of oceanic methane emissions. Also, estuaries are intermediate zones between methane-rich river water and methane depleted marine water. Substantiated through this thesis at the example of the Elbe estuary, the methane distribution in estuaries, however, cannot entirely be described by the conservative mixing model i.e. gradual decrease from the freshwater end-member to the marine water end-member. In addition to the methane-rich water from the Elbe River mouth substantial methane input occurs from tidal flats, areas of significant interaction between aquatic and terrestrial environments. Thus, this study demonstrates the complex interactions and their consequences for the methane distribution within estuaries. Also it reveals how important it is to investigate estuaries at larger spatial scales.
Methane oxidation (MOX) rates are commonly correlated with methane concentrations. This was shown in previous research studies and was substantiated by the present thesis. In detail, the highest MOX rates in the Arctic water bodies were detected in methane-rich streams and in the floodplain area while in the Elbe estuary the highest MOX rates were observed at the coastal stations. However, in these bordering environments, MOX rates are affected not only via the regulation through methane concentrations. The MOX rates in the Arctic lakes were shown to be also dependent on the abundance and community composition of methane-oxidising bacteria (MOB), that in turn are controlled by local landscape features (regardless of the methane concentrations) and by the transport of MOB between neighbouring environments. In the Elbe estuary, the MOX rates in addition to the methane concentrations are largely affected by the salinity, which is in turn regulated by the mixing of fresh- and marine waters. The magnitude of the salinity impact on MOX rates thereby depends on the MOB community composition and on the rate of the salinity change.
This study extends our knowledge of environmental controls of methane distribution and aerobic methane oxidation in aquatic environments. It also illustrates how important it is to investigate complex ecosystems rather than individual ecosystems to better understand the functioning of whole biomes.
Die Elbe und ihr Einzugsgebiet sind vom Klimawandel betroffen. Um die Wirkkette von projizierten Klimaveränderungen auf den Wasserhaushalt und die daraus resultierenden Nährstoffeinträge und -frachten für große Einzugsgebiete wie das der Elbe zu analysieren, können integrierte Umweltmodellsysteme eingesetzt werden. Fallstudien, die mit diesen Modellsystemen ad hoc durchgeführt werden, repräsentieren den Istzustand von Modellentwicklungen und -unsicherheiten und sind damit statisch.
Diese Arbeit beschreibt den Einstieg in die Dynamisierung von Klimafolgenanalysen im Elbegebiet. Dies umfasst zum einen eine Plausibilitätsprüfung von Auswirkungsrechnungen, die mit Szenarien des statistischen Szenariengenerators STARS durchgeführt wurden, durch den Vergleich mit den Auswirkungen neuerer Klimaszenarien aus dem ISI-MIP Projekt, die dem letzten Stand der Klimamodellierung entsprechen. Hierfür wird ein integriertes Modellsystem mit "eingefrorenem Entwicklungsstand" verwendet. Die Klimawirkungsmodelle bleiben dabei unverändert. Zum anderen wird ein Bestandteil des integrierten Modellsystems – das ökohydrologische Modell SWIM – zu einer "live"-Version weiterentwickelt. Diese wird durch punktuelle Testung an langjährigen Versuchsreihen eines Lysimeterstandorts sowie an aktuellen Abflussreihen validiert und verbessert.
Folgende Forschungsfragen werden bearbeitet: (i) Welche Effekte haben unterschiedliche Klimaszenarien auf den Wasserhaushalt im Elbegebiet und ist eine Neubewertung der Auswirkung des Klimawandels auf den Wasserhaushalt notwendig?, (ii) Was sind die Auswirkungen des Klimawandels auf die Nährstoffeinträge und -frachten im Elbegebiet sowie die Wirksamkeit von Maßnahmen zur Reduktion der Nährstoffeinträge?, (iii) Ist unter der Nutzung (selbst einer sehr geringen Anzahl) verfügbarer tagesaktueller Witterungsdaten in einem stark heterogenen Einzugsgebiet eine valide Ansprache der aktuellen ökohydrologischen Situation des Elbeeinzugsgebiets möglich?
Die aktuellen Szenarien bestätigen die Richtung, jedoch nicht das Ausmaß der Klimafolgen: Die Rückgänge des mittleren jährlichen Gesamtabflusses und der monatlichen Abflüsse an den Pegeln bis Mitte des Jahrhunderts betragen für das STARS-Szenario ca. 30 %. Die Rückgänge bei den auf dem ISI-MIP-Szenario basierenden Modellstudien liegen hingegen nur bei ca. 10 %. Hauptursachen für diese Divergenz sind die Unterschiede in den Niederschlagsprojektionen sowie die Unterschiede in der jahreszeitlichen Verteilung der Erwärmung. Im STARS-Szenario gehen methodisch bedingt die Niederschläge zurück und der Winter erwärmt sich stärker als der Sommer. In dem ISI-MIP-Szenario bleiben die Niederschläge nahezu stabil und die Erwärmung im Sommer und Winter unterscheidet sich nur geringfügig.
Generell nehmen die Nährstoffeinträge und -frachten mit den Abflüssen in beiden Szenarien unterproportional ab, wobei die Frachten jeweils stärker als die Einträge zurückgehen. Die konkreten Effekte der Abflussänderungen sind gering und liegen im einstelligen Prozentbereich. Gleiches gilt für die Unterschiede zwischen den Szenarien. Der Effekt von zwei ausgewählten Maßnahmen zur Reduktion der Nährstoffeinträge und -frachten unterscheidet sich bei verschiedenen Abflussverhältnissen, repräsentiert durch unterschiedliche Klimaszenarien in unterschiedlich feuchter Ausprägung, ebenfalls nur geringfügig.
Die Beantwortung der ersten beiden Forschungsfragen zeigt, dass die Aktualisierung von Klimaszenarien in einem ansonsten "eingefrorenen" Verbund von ökohydrologischen Daten und Modellen eine wichtige Prüfoption für die Plausibilisierung von Klimafolgenanalysen darstellt. Sie bildet die methodische Grundlage für die Schlussfolgerung, dass bei der Wassermenge eine Neubewertung der Klimafolgen notwendig ist, während dies bei den Nährstoffeinträgen und -frachten nicht der Fall ist.
Die zur Beantwortung der dritten Forschungsfrage mit SWIM-live durchgeführten Validierungsstudien ergeben Diskrepanzen am Lysimeterstandort und bei den Abflüssen aus den Teilgebieten Saale und Spree. Sie lassen sich zum Teil mit der notwendigen Interpolationsweite der Witterungsdaten und dem Einfluss von Wasserbewirtschaftungsmaßnahmen erklären. Insgesamt zeigen die Validierungsergebnisse, dass schon die Pilotversion von SWIM-live für eine ökohydrologische Ansprache des Gebietswasserhaushaltes im Elbeeinzugsgebiet genutzt werden kann. SWIM-live ermöglicht eine unmittelbare Betrachtung und Beurteilung simulierter Daten. Dadurch werden Unsicherheiten bei der Modellierung direkt offengelegt und können infolge dessen reduziert werden. Zum einen führte die Verdichtung der meteorologischen Eingangsdaten durch die Verwendung von nun ca. 700 anstatt 19 Klima- bzw. Niederschlagstationen zu einer Verbesserung der Ergebnisse. Zum anderen wurde SWIM-live beispielhaft für einen Zyklus aus punktueller Modellverbesserung und flächiger Überprüfung der Simulationsergebnisse genutzt.
Die einzelnen Teilarbeiten tragen jeweils zur Dynamisierung von Klimafolgenanalysen im Elbegebiet bei. Der Anlass hierfür war durch die fehlerhaften methodischen Grundlagen von STARS gegeben. Die Sinnfälligkeit der Dynamisierung ist jedoch nicht an diesen konkreten Anlass gebunden, sondern beruht auf der grundlegenden Einsicht, dass Ad-hoc-Szenarienanalysen immer auch pragmatische Vereinfachungen zugrunde liegen, die fortlaufend überprüft werden müssen.
Fossil oyster shells are well-suited to provide palaeotemperature proxies from geologic to seasonal timescales due to their ubiquitous occurrence from Triassic to Quaternary sediments, the seasonal nature of their shell growth and their relative strong resistance to post-mortem alteration. However, the common use to translate calcitic oxygen isotopes into palaeotemperatures is challenged by uncertainties in accounting for past seawater delta O-18, especially in shallow coastal environment where oysters calcify. In principle, the Mg/Ca ratio in oyster shells can provide an alternative palaeothermometer. Several studies provided temperature calibrations for this potential proxy based on modem species, nevertheless their application to palaeo-studies remains hitherto unexplored. Here, we show that past temperature variability in seawater can be obtained from Mg/Ca analyses from selected fossil oyster species and specimens. High-resolution Mg/Ca profiles, combined with delta O-18, were obtained along 41 fossil oyster shells of seven different species from the Palaeogene Proto-Paratethys sea (Central Asia) found in similar as well as different depositional age and environments providing comparison. Suitable Mg/Ca profiles, defined by continuous cyclicity and reproducibility within one shell, are found to be consistent for specimens of the same species but differ systematically between species, implying a dominant species-specific effect on the Mg/Ca signal. Two species studied here (Ostrea (Turkostrea) strictiplicata and Sokolowia buhsii) provide an excellent proxy for palaeoclimate reconstruction from China to Europe in Palaeogene marine sediments. More generally, the protocol developed here can be applied to identify other fossil oyster species suitable for palaeoclimate reconstructions. (C) 2015 Elsevier B.V. All rights reserved.
Permafrost-related processes drive regional landscape dynamics in the Arctic terrestrial system. A better understanding of past periods indicative of permafrost degradation and aggradation is important for predicting the future response of Arctic landscapes to climate change. Here, we used a multi-proxy approach to analyse a4m long sediment core from a drained thermokarst lake basin on the northern Seward Peninsula in western Arctic Alaska (USA). Sedimentological, biogeochemical, geochronological, micropalaeontological (ostracoda, testate amoebae) and tephra analyses were used to determine the long-term environmental Early-Wisconsin to Holocene history preserved in our core for central Beringia. Yedoma accumulation dominated throughout the Early to Late-Wisconsin but was interrupted by wetland formation from 44.5 to 41.5ka BP. The latter was terminated by the deposition of 1m of volcanic tephra, most likely originating from the South Killeak Maar eruption at about 42ka BP. Yedoma deposition continued until 22.5ka BP and was followed by a depositional hiatus in the sediment core between 22.5 and 0.23ka BP. We interpret this hiatus as due to intense thermokarst activity in the areas surrounding the site, which served as a sediment source during the Late-Wisconsin to Holocene climate transition. The lake forming the modern basin on the upland initiated around 0.23ka BP and drained catastrophically in spring 2005. The present study emphasises that Arctic lake systems and periglacial landscapes are highly dynamic and that permafrost formation as well as degradation in central Beringia was controlled by regional to global climate patterns as well as by local disturbances. Copyright (c) 2015 John Wiley & Sons, Ltd.
Rainfall in the central Andes associated with the South American Monsoon and the South American Low-Level Jet results from orographic effects on atmospheric circulation exerted by the Andean Plateau and the Eastern Cordillera. However, despite its importance for South American climate, no reliable records exist that allow decoding the evolution of thresholds and interactions between Andean topography and atmospheric circulation, especially regarding the onset of humid conditions in the inherently dry southern central Andes. Here, we employ multi-proxy isotope data of lipid biomarkers, pedogenic carbonates and volcanic glass from the Eastern Cordillera of NW Argentina and present the first long-term evapotranspiration record. We find that regional eco-hydrology and vegetation changes are associated with initiation of moisture transport via the South American Low-Level Jet at 7.6 Ma, and subsequent lateral growth of the orogen at 6.5 Ma. Our results highlight that topographically induced changes in atmospheric circulation patterns, not global climate change, were responsible for late Miocene environmental change in this part of the southern hemisphere. This suggests that mountain building over time fundamentally controlled habitat evolution along the central Andes.
BACKROUND: Few studies have been carried out to connect nutrients recovery from wastewater and heavy metals immobilization in contaminated soil. To achieve the goal, ammonia nitrogen (AN) and phosphorus (P) were recovered from rare-earth wastewater by using the formation of struvite, which was used as the amendment with plant ash for copper, lead and chromium immobilization. RESULTS: AN removal efficiency and residual P reached 95.32 +/- 0.73% and 6.14 +/- 1.72mgL(-1) under optimal conditions: pH= 9.0, n(Mg): n(N): n(P)= 1.2: 1: 1.1, which were obtained using response surface methodology (RSM). The minimum available concentrations of Cu, Pb and Cr (CPC) separately reduced to 320.82 mg kg(-1), 190.77 mg kg(-1) and 121.46 mg kg(-1) with increasing immobilization time at the mass ratio of phosphate precipitate (PP)/plant ash (PA) of 1: 3. Humic acid (HA) and fulvic acid (FA) were beneficial to immobilize Cu, both of which showed no effect or even a negative effect on Pb and Cr immobilization.
Decreasing groundwater levels in many parts of Germany and decreasing low flows in Central Europe have created a need for adaptation measures to stabilize the water balance and to increase low flows. The objective of our study was to estimate the impact of ditch water level management on stream-aquifer interactions in small lowland catchments of the mid-latitudes. The water balance of a ditch-irrigated area and fluxes between the subsurface and the adjacent stream were modeled for three runoff recession periods using the Hydrus-2D software package. The results showed that the subsurface flow to the stream was closely related to the difference between the water level in the ditch system and the stream. Evapotranspiration during the growing season additionally reduced base flow. It was crucial to stop irrigation during a recession period to decrease water withdrawal from the stream and enhance the base flow by draining the irrigated area. Mean fluxes to the stream were between 0.04 and 0.64 ls(-1) for the first 20 days of the low-flow periods. This only slightly increased the flow in the stream, whose mean was 57 ls(-1) during the period with the lowest flows. Larger areas would be necessary to effectively increase flows in mesoscale catchments.
Decreasing groundwater levels in many parts of Germany and decreasing low flows in Central Europe have created a need for adaptation measures to stabilize the water balance and to increase low flows. The objective of our study was to estimate the impact of ditch water level management on stream-aquifer interactions in small lowland catchments of the mid-latitudes. The water balance of a ditch-irrigated area and fluxes between the subsurface and the adjacent stream were modeled for three runoff recession periods using the Hydrus-2D software package. The results showed that the subsurface flow to the stream was closely related to the difference between the water level in the ditch system and the stream. Evapotranspiration during the growing season additionally reduced base flow. It was crucial to stop irrigation during a recession period to decrease water withdrawal from the stream and enhance the base flow by draining the irrigated area. Mean fluxes to the stream were between 0.04 and 0.64 ls(-1) for the first 20 days of the low-flow periods. This only slightly increased the flow in the stream, whose mean was 57 ls(-1) during the period with the lowest flows. Larger areas would be necessary to effectively increase flows in mesoscale catchments.
During expedition 202 aboard the RV Sonne in 2009, 39 seafloor surface sediment sites were sampled over a wide sector of the North Pacific and adjoining Bering Sea. The data served to infer land-ocean linkages of terrigenous sediment supply in terms of major sources and modes of sediment transport within an over-regional context. This is based on an integrated approach dealing with grain-size analysis, bulk mineralogy and clay mineralogy in combination with statistical data evaluation (end-member modelling of grain-size data, fuzzy cluster analysis of mineralogical data). The findings on clay mineralogy served to update those of earlier work extracted from the literature. Today, two processes of terrigenous sediment supply prevail in the study area: far-distance aeolian sediment supply to the pelagic North Pacific, and hemipelagic sediment dispersal from nearby land sources via ocean currents along the continental margins and island arcs. Aeolian particles show the finest grain sizes (clay and fine silt), whereas hemipelagic sediments have high abundances of coarse silt. Exposed sites on seamounts and the continental slope are partly swept by strong currents, leading to residual enrichment of fine sand. Four sediment sources can be distinguished on the basis of distinct index minerals revealed by statistical data analysis: dust plumes from central Asia (quartz, illite), altered materials from the volcanic regions of Kamchatka and the Aleutian Arc (smectite), detritus from the Alaskan Cordillera (chlorite, hornblende), and fluvial detritus from far-eastern Siberia and the Alaska mainland (quartz, feldspar, illite). These findings confirm those of former studies but considerably expand the geographic range of this suite of proxies as far south as 39A degrees N in the open North Pacific. The present integrated methodological approach proved useful in identifying the major modern processes of terrigenous sediment supply to the study region. This aspect deserves attention in the selection of sediment core sites for future palaeoenvironmental reconstructions related to aeolian and glacial dynamics, as well as the recognition of palaeo-ocean circulation patterns in general.
Molecular Paleoclimate Reconstructions over the Last 9 ka from a Peat Sequence in South China
(2016)
To achieve a better understanding of Holocene climate change in the monsoon regions of China, we investigated the molecular distributions and carbon and hydrogen isotope compositions delta C-13 and delta D values) of long-chain n-alkanes in a peat core from the Shiwangutian SWGT) peatland, south China over the last 9 ka. By comparisons with other climate records, we found that the delta C-13 values of the long-chain n-alkanes can be a proxy for humidity, while the dD values of the long-chain n-alkanes primarily recorded the moisture source dD signal during 9-1.8 ka BP and responded to the dry climate during 1.8-0.3 ka BP. Together with the average chain length ACL) and the carbon preference index CPI) data, the climate evolution over last 9 ka in the SWGT peatland can be divided into three stages. During the first stage 9-5 ka BP), the delta C-13 values were depleted and CPI and Paq values were low, while ACL values were high. They reveal a period of warm and wet climate, which is regarded as the Holocene optimum. The second stage 5-1.8 ka BP) witnessed a shift to relatively cool and dry climate, as indicated by the more positive delta C-13 values and lower ACL values. During the third stage 1.8-0.3 ka BP), the delta C-13, delta D, CPI and Paq values showed marked increase and ACL values varied greatly, implying an abrupt change to cold and dry conditions. This climate pattern corresponds to the broad decline in Asian monsoon intensity through the latter part of the Holocene. Our results do not support a later Holocene optimum in south China as suggested by previous studies.
Monitoring the phase space of ecosystems: Concept and examples from the Quillow catchment, Uckermark
(2016)
Ecosystem research benefits enormously from the fact that comprehensive data sets of high quality, and covering long time periods are now increasingly more available. However, facing apparently complex interdependencies between numerous ecosystem components, there is urgent need rethinking our approaches in ecosystem research and applying new tools of data analysis. The concept presented in this paper is based on two pillars. Firstly, it postulates that ecosystems are multiple feedback systems and thus are highly constrained. Consequently, the effective dimensionality of multivariate ecosystem data sets is expected to be rather low compared to the number of observables. Secondly, it assumes that ecosystems are characterized by continuity in time and space as well as between entities which are often treated as distinct units. Implementing this concept in ecosystem research requires new tools for analysing large multivariate data sets. This study presents some of them, which were applied to a comprehensive water quality data set from a long-term monitoring program in Northeast Germany in the Uckermark region, one of the LTER-D (Long Term Ecological Research network, Germany) sites. Short-term variability of the kettle hole water samples differed substantially from that of the stream water samples, suggesting different processes generating the dynamics in these two types of water bodies. However, again, this seemed to be due to differing intensities of single processes rather than to completely different processes. We feel that research aiming at elucidating apparently complex interactions in ecosystems could make much more efficient use from now available large monitoring data sets by implementing the suggested concept and using corresponding innovative tools of system analysis. (C) 2015 Elsevier Ltd. All rights reserved.
New tools and algorithms for geological femote Sensing are developed and verified at test sites throughout the world in preparation of the German hyperspectral satellite Mission (EnMAP), which is an Environmental Mapping and Analysis Program. The aggeneys Cu-Pb-Zn deposit, situated in the arid north western part of South Africa, represents a unique field laboratory for testing these new tools. Here spaceborne hyperspectral data covering the Swartberg, and hyperspectral spaceborne data can be demonkrated, such as the Iron Feature Depth index (IFD), which has recently been proposed for mine waste mapping in the North West Province of South Africa and for gossan detection at Haib River in South Namibia. The work presented here explores the potential of the IFD for gossan mapping and characterization at Gamsberg and Big Syncline, from EO-1 ALI and Landsat-8 OLI data together with mineral maps from expert systems such as the United States Geological Survey (USGS) Material Identification and Characterization Algorithm (MICA), and first results from EnMAPs EnGeoMAP algorithm. Field spectroscopic measurements and field sampling were carried out to validate and calibrate the results from the expert systems and the IFD. This ground truthing is a necessary complementary step to link the results from the expert systems and the IFD to in-situ field spectroscopy. Future mineral exploration initiatives may benefit from the techniques described here, because they can significantly narrow the expensive, exploration activities such as hyperspectral airborne data, field activities and drilling, by identifying the most promising mineral anomalies in an area from the spaceborne data.
Many German lakes experienced significant water level declines in recent decades that are not fully understood due to the short observation period. At a typical northeastern German groundwater-fed lake with a complex basin morphology, an acoustic sub-bottom profile was analysed together with a transect of five sediment cores, which were correlated using multiple proxies (sediment facies, -XRF, macrofossils, subfossil Cladocera). Shifts in the boundary between sand and mud deposition were controlled by lake level changes, and hence, allowed the quantification of an absolute lake level amplitude of similar to 8m for the Holocene. This clearly exceeded observed modern fluctuations of 1.3m (AD 1973-2010). Past lake level changes were traced continuously using the calcium-record. During high lake levels, massive organic muds were deposited in the deepest lake basin, whereas lower lake levels isolated the sub-basins and allowed carbonate deposition. During the beginning of the Holocene (>9700cal. a BP), lake levels were high, probably due to final melting of permafrost and dead-ice remains. The establishment of water-use intensive Pinus forests caused generally low (3-4m below modern) but fluctuating lake levels (9700-6400cal. a BP). Afterwards, the lake showed an increasing trend and reached a short-term highstand at c.5000cal. a BP (4m above modern). At the transition towards a cooler and wetter late Holocene, forests dominated by Quercus and Fagus and initial human impact probably contributed more positively to groundwater recharge. Lake levels remained high between 3800 and 800cal. a BP, but the lake system was not sensitive enough to record short-term fluctuations during this period. Lake level changes were recorded again when humans profoundly affected the drainage system, land cover and lake trophy. Hence, local Holocene water level changes reflect feedbacks between catchment and vegetation characteristics and human impact superimposed by climate change at multiple temporal scales.
The 11 July 1889 Chilik earthquake (M-w 8.0-8.3) forms part of a remarkable sequence of large earthquakes in the late nineteenth and early twentieth centuries in the northern Tien Shan. Despite its importance, the source of the 1889 earthquake remains unknown, though the macroseismic epicenter is sited in the Chilik valley, similar to 100 km southeast of Almaty, Kazakhstan (similar to 2 million population). Several short fault segments that have been inferred to have ruptured in 1889 are too short on their own to account for the estimated magnitude. In this paper we perform detailed surveying and trenching of the similar to 30 km long Saty fault, one of the previously inferred sources, and find that it was formed in a single earthquake within the last 700 years, involving surface slip of up to 10 m. The scarp-forming event, likely to be the 1889 earthquake, was the only surface-rupturing event for at least 5000 years and potentially for much longer. From satellite imagery we extend the mapped length of fresh scarps within the 1889 epicentral zone to a total of similar to 175 km, which we also suggest as candidate ruptures from the 1889 earthquake. The 175 km of rupture involves conjugate oblique left-lateral and right-lateral slip on three separate faults, with step overs of several kilometers between them. All three faults were essentially invisible in the Holocene geomorphology prior to the last slip. The recurrence interval between large earthquakes on any of these faults, and presumably on other faults of the Tien Shan, may be longer than the timescale over which the landscape is reset, providing a challenge for delineating sources of future hazard.
The collision of bathymetric anomalies, such as oceanic spreading centers, at convergent plate margins can profoundly affect subduction dynamics, magmatism, and the structural and geomorphic evolution of the overriding plate. The Southern Patagonian Andes of South America are a prime example for sustained oceanic ridge collision and the successive formation and widening of an extensive asthenospheric slab window since the Middle Miocene. Several of the predicted upper-plate geologic manifestations of such deep-seated geodynamic processes have been studied in this region, but many topics remain highly debated. One of the main controversial topics is the interpretation of the regional low-temperature thermochronology exhumational record and its relationship with tectonic and/or climate-driven processes, ultimately manifested and recorded in the landscape evolution of the Patagonian Andes. The prominent along-strike variance in the topographic characteristics of the Andes, combined with coupled trends in low-temperature thermochronometer cooling ages have been interpreted in very contrasting ways, considering either purely climatic (i.e. glacial erosion) or geodynamic (slab-window related) controlling factors.
This thesis focuses on two main aspects of these controversial topics. First, based on field observations and bedrock low-temperature thermochronology data, the thesis addresses an existing research gap with respect to the neotectonic activity of the upper plate in response to ridge collision - a mechanism that has been shown to affect the upper plate topography and exhumational patterns in similar tectonic settings. Secondly, the qualitative interpretation of my new and existing thermochronological data from this region is extended by inverse thermal modelling to define thermal histories recorded in the data and evaluate the relative importance of surface vs. geodynamic factors and their possible relationship with the regional cooling record.
My research is centered on the Northern Patagonian Icefield (NPI) region of the Southern Patagonian Andes. This site is located inboard of the present-day location of the Chile Triple Junction - the juncture between the colliding Chile Rise spreading center and the Nazca and Antarctic Plates along the South American convergent margin. As such this study area represents the region of most recent oceanic-ridge collision and associated slab window formation. Importantly, this location also coincides with the abrupt rise in summit elevations and relief characteristics in the Southern Patagonian Andes. Field observations, based on geological, structural and geomorphic mapping, are combined with bedrock apatite (U-Th)/He and apatite fission track (AHe and AFT) cooling ages sampled along elevation transects across the orogen. This new data reveals the existence of hitherto unrecognized neotectonic deformation along the flanks of the range capped by the NPI.
This deformation is associated with the closely spaced oblique collision of successive oceanic-ridge segments in this region over the past 6 Ma. I interpret that this has caused a crustal-scale partitioning of deformation and the decoupling, margin-parallel migration, and localized uplift of a large crustal sliver (the NPI block) along the subduction margin. The location of this uplift coincides with a major increase of summit elevations and relief at the northern edge of the NPI massif. This mechanism is compatible with possible extensional processes along the topographically subdued trailing edge of the NPI block as documented by very recent and possibly still active normal faulting. Taken together, these findings suggest a major structural control on short-wavelength variations in topography in the Southern Patagonian Andes - the region affected by ridge collision and slab window formation.
The second research topic addressed here focuses on using my new and existing bedrock low-temperature cooling ages in forward and inverse thermal modeling. The data was implemented in the HeFTy and QTQt modeling platforms to constrain the late Cenozoic thermal history of the Southern Patagonian Andes in the region of the most recent upper-plate sectors of ridge collision. The data set combines AHe and AFT data from three elevation transects in the region of the Northern Patagonian Icefield. Previous similar studies claimed far-reaching thermal effects of the approaching ridge collision and slab window to affect patterns of Late Miocene reheating in the modelled thermal histories. In contrast, my results show that the currently available data can be explained with a simpler thermal history than previously proposed. Accordingly, a reheating event is not needed to reproduce the observations. Instead, the analyzed ensemble of modelled thermal histories defines a Late Miocene protracted cooling and Pliocene-to-recent stepwise exhumation. These findings agree with the geological record of this region. Specifically, this record indicates an Early Miocene phase of active mountain building associated with surface uplift and an active fold-and-thrust belt, followed by a period of stagnating deformation, peneplanation, and lack of synorogenic deposition in the Patagonian foreland. The subsequent period of stepwise exhumation likely resulted from a combination of pulsed glacial erosion and coeval neotectonic activity. The differences between the present and previously published interpretation of the cooling record can be reconciled with important inconsistencies of previously used model setup. These include mainly the insufficient convergence of the models and improper assumptions regarding the geothermal conditions in the region. This analysis puts a methodological emphasis on the prime importance of the model setup and the need for its thorough examination to evaluate the robustness of the final outcome.
This paper addresses the lithosphere-scale subduction-collision history of the eastern termination of the Aegean retreating subduction system, i.e. western Anatolia. Although there is some general consensus on the protracted subduction evolution of the Aegean since the early Cenozoic at least, correlation with western Anatolia has been widely debated for more than several decades. In western Anatolia, three main tectonic configurations have been envisaged in the past years to reconstruct slab dynamics during the closure of the Neotethyan oceanic realm since the Late Cretaceous. Some authors have suggested an Aegean-type scenario, with the continuous subduction of a single lithospheric slab, punctuated by episodic slab roll-back and trench retreat, whereas others assumed a discontinuous subduction history marked by intermittent slab break-off during either the Campanian (ca. 75 Ma) or the Early Eocene (ca. 55-50 Ma). The third view implies three partly contemporaneous subduction zones. Our review of these models points to key debated aspects that can be re-evaluated in the light of multidisciplinary constraints from the literature. Our discussion leads us to address the timing of subduction initiation, the existence of hypothetical ocean basins, the number of intervening subduction zones between the Taurides and the Pontides, the palaeogeographic origin of tectonic units and the possibility for slab break-off during either the Campanian or the Early Eocene. Thence, we put forward a favoured tectonic scenario featuring two successive phases of subduction of a single lithospheric slab and episodic accretion of two continental domains separated by a continental trough, representing the eastern end of the Cycladic Ocean of the Aegean. The lack of univocal evidence for slab break-off in western Anatolia and southward-younging HP/LT metamorphism in continental tectonic units (from similar to 85, 70 to 50 Ma) in the Late Cretaceous-Palaeogene period suggests continuous subduction since similar to 110 Ma, marked by roll-back episodes in the Palaeocene and the Oligo-Miocene, and slab tearing below western Anatolia during the Miocene.
The Dead Sea region has faced substantial environmental challenges in recent decades, including water resource scarcity, similar to 1 m annual decreases in the water level, sinkhole development, ascending-brine freshwater pollution, and seismic disturbance risks. Natural processes are significantly affected by human interference as well as by climate change and tectonic developments over the long term. To get a deep understanding of processes and their interactions, innovative scientific approaches that integrate disciplinary research and education are required. The research project DESERVE (Helmholtz Virtual Institute Dead Sea Research Venue) addresses these challenges in an interdisciplinary approach that includes geophysics, hydrology, and meteorology. The project is implemented by a consortium of scientific institutions in neighboring countries of the Dead Sea (Israel, Jordan, Palestine Territories) and participating German Helmholtz Centres (KIT, GFZ, UFZ). A new monitoring network of meteorological, hydrological, and seismic/geodynamic stations has been established, and extensive field research and numerical simulations have been undertaken. For the first time, innovative measurement and modeling techniques have been applied to the extreme conditions of the Dead Sea and its surroundings. The preliminary results show the potential of these methods. First time ever performed eddy covariance measurements give insight into the governing factors of Dead Sea evaporation. High-resolution bathymetric investigations reveal a strong correlation between submarine springs and neo-tectonic patterns. Based on detailed studies of stratigraphy and borehole information, the extension of the subsurface drainage basin of the Dead Sea is now reliably estimated. Originality has been achieved in monitoring flash floods in an arid basin at its outlet and simultaneously in tributaries, supplemented by spatio-temporal rainfall data. Low-altitude, high resolution photogrammetry, allied to satellite image analysis and to geophysical surveys (e.g. shear-wave reflections) has enabled a more detailed characterization of sinkhole morphology and temporal development and the possible subsurface controls thereon. All the above listed efforts and scientific results take place with the interdisciplinary education of young scientists. They are invited to attend joint thematic workshops and winter schools as well as to participate in field experiments. (C) 2015 The Authors. Published by Elsevier B.V.
Non-linear time series analysis of precipitation events using regional climate networks for Germany
(2016)
Synchronous occurrences of heavy rainfall events and the study of their relation in time and space are of large socio-economical relevance, for instance for the agricultural and insurance sectors, but also for the general well-being of the population. In this study, the spatial synchronization structure is analyzed as a regional climate network constructed from precipitation event series. The similarity between event series is determined by the number of synchronous occurrences. We propose a novel standardization of this number that results in synchronization scores which are not biased by the number of events in the respective time series. Additionally, we introduce a new version of the network measure directionality that measures the spatial directionality of weighted links by also taking account of the effects of the spatial embedding of the network. This measure provides an estimate of heavy precipitation isochrones by pointing out directions along which rainfall events synchronize. We propose a climatological interpretation of this measure in terms of propagating fronts or event traces and confirm it for Germany by comparing our results to known atmospheric circulation patterns.
A Paleoarchean impact spherule-bearing interval of the 763 m long International Continental Scientific Drilling Program (ICDP) drill core BARB5 from the lower Mapepe Formation of the Fig Tree Group, Barberton Mountain Land (South Africa) was investigated using nondestructive analytical techniques. The results of visual observation, infrared (IR) spectroscopic imaging, and micro-X-ray fluorescence (lXRF) of drill cores are presented. Petrographic and sedimentary features, as well as major and trace element compositions of lithologies from the micrometer to kilometer-scale, assisted in the localization and characterization of eight spherule-bearing intervals between 512.6 and 510.5 m depth. The spherule layers occur in a strongly deformed section between 517 and 503 m, and the rocks in the core above and below are clearly less disturbed. The lXRF element maps show that spherule layers have similar petrographic and geochemical characteristics but differences in (1) sorting of two types of spherules and (2) occurrence of primary minerals (Ni-Cr spinel and zircon). We favor a single impact scenario followed by postimpact reworking, and subsequent alteration. The spherule layers are Al2O3-rich and can be distinguished from the Al2O3-poor marine sediments by distinct Al-OH absorption features in the short wave infrared (SWIR) region of the electromagnetic spectrum. Infrared images can cover tens to hundreds of square meters of lithologies and, thus, may be used to search for Al-OH-rich spherule layers in Al2O3-poor sediments, such as Eoarchean metasediments, where the textural characteristics of the spherule layers are obscured by metamorphism.
Oceanic lithospheric S-wave velocities from the analysis of P-wave polarization at the ocean floor
(2016)
Our knowledge of the absolute S-wave velocities of the oceanic lithosphere is mainly based on global surface wave tomography, local active seismic or compliance measurements using oceanic infragravity waves. The results of tomography give a rather smooth picture of the actual S-wave velocity structure and local measurements have limitations regarding the range of elastic parameters or the geometry of the measurement. Here, we use the P-wave polarization (apparent P-wave incidence angle) of teleseismic events to investigate the S-wave velocity structure of the oceanic crust and the upper tens of kilometres of the mantle beneath single stations. In this study, we present an up to our knowledge new relation of the apparent P-wave incidence angle at the ocean bottom dependent on the half-space S-wave velocity. We analyse the angle in different period ranges at ocean bottom stations (OBSs) to derive apparent S-wave velocity profiles. These profiles are dependent on the S-wave velocity as well as on the thickness of the layers in the subsurface. Consequently, their interpretation results in a set of equally valid models. We analyse the apparent P-wave incidence angles of an OBS data set which was collected in the Eastern Mid Atlantic. We are able to determine reasonable S-wave-velocity-depth models by a three-step quantitative modelling after a manual data quality control, although layer resonance sometimes influences the estimated apparent S-wave velocities. The apparent S-wave velocity profiles are well explained by an oceanic PREM model in which the upper part is replaced by four layers consisting of a water column, a sediment, a crust and a layer representing the uppermost mantle. The obtained sediment has a thickness between 0.3 and 0.9 km with S-wave velocities between 0.7 and 1.4 km s(-1). The estimated total crustal thickness varies between 4 and 10 km with S-wave velocities between 3.5 and 4.3 km s(-1). We find a slight increase of the total crustal thickness from similar to 5 to similar to 8 km towards the South in the direction of a major plate boundary, the Gloria Fault. The observed crustal thickening can be related with the known dominant compression in the vicinity of the fault. Furthermore, the resulting mantle S-wave velocities decrease from values around 5.5 to 4.5 km s(-1) towards the fault. This decrease is probably caused by serpentinization and indicates that the oceanic transform fault affects a broad region in the uppermost mantle. Conclusively, the presented method is useful for the estimation of the local S-wave velocity structure beneath ocean bottom seismic stations. It is easy to implement and consists of two main steps: (1) measurement of apparent P-wave incidence angles in different period ranges for real and synthetic data, and (2) comparison of the determined apparent S-wave velocities for real and synthetic data to estimate S-wave velocity-depth models.
The functional form of empirical response spectral ground-motion prediction equations (GMPEs) is often derived using concepts borrowed from Fourier spectral modeling of ground motion. As these GMPEs are subsequently calibrated with empirical observations, this may not appear to pose any major problems in the prediction of ground motion for a particular earthquake scenario. However, the assumption that Fourier spectral concepts persist for response spectra can lead to undesirable consequences when it comes to the adjustment of response spectral GMPEs to represent conditions not covered in the original empirical data set. In this context, a couple of important questions arise, for example, what are the distinctions and/or similarities between Fourier and response spectra of ground motions? And, if they are different, then what is the mechanism responsible for such differences and how do adjustments that are made to Fourier amplitude spectrum (FAS) manifest in response spectra? The present article explores the relationship between the Fourier and response spectrum of ground motion by using random vibration theory (RVT). With a simple Brune (1970, 1971) source model, RVT-generated acceleration spectra for a fixed magnitude and distance scenario are used. The RVT analyses reveal that the scaling of low oscillator-frequency response spectral ordinates can be treated as being equivalent to the scaling of the corresponding Fourier spectral ordinates. However, the high oscillator-frequency response spectral ordinates are controlled by a rather wide band of Fourier spectral ordinates. In fact, the peak ground acceleration, counter to the popular perception that it is a reflection of the high-frequency characteristics of ground motion, is controlled by the entire Fourier spectrum of ground motion. Additionally, this article demonstrates how an adjustment made to FAS is similar or different to the same adjustment made to response spectral ordinates. For this purpose, two cases: adjustments to the stress parameter (Delta sigma) (source term), and adjustments to the attributes reflecting site response (V-S - kappa(0)) are considered.
Isostasy is one of the oldest and most widely applied concepts in the geosciences, but the geoscientific community lacks a coherent, easy-to-use tool to simulate flexure of a realistic (i.e., laterally heterogeneous) lithosphere under an arbitrary set of surface loads. Such a model is needed for studies of mountain building, sedimentary basin formation, glaciation, sea-level change, and other tectonic, geodynamic, and surface processes. Here I present gFlex (for GNU flexure), an open-source model that can produce analytical and finite difference solutions for lithospheric flexure in one (profile) and two (map view) dimensions. To simulate the flexural isostatic response to an imposed load, it can be used by itself or within GRASS GIS for better integration with field data. gFlex is also a component with the Community Surface Dynamics Modeling System (CSDMS) and Landlab modeling frameworks for coupling with a wide range of Earth-surface-related models, and can be coupled to additional models within Python scripts. As an example of this in-script coupling, I simulate the effects of spatially variable lithospheric thickness on a modeled Iceland ice cap. Finite difference solutions in gFlex can use any of five types of boundary conditions: 0-displacement, 0-slope (i.e., clamped); 0-slope, 0-shear; 0-moment, 0-shear (i.e., broken plate); mirror symmetry; and periodic. Typical calculations with gFlex require << 1 s to similar to 1 min on a personal laptop computer. These characteristics - multiple ways to run the model, multiple solution methods, multiple boundary conditions, and short compute time - make gFlex an effective tool for flexural isostatic modeling across the geosciences.
The Paleocene was a time of transition for the Arctic, with magmatic activity of the High Arctic Large Igneous Province (HALIP) giving way to magmatism of the North Atlantic Large Igneous Province in connection to plate tectonic changes in the Arctic and North Atlantic. In this study we investigate the Paleocene magmatic record and sediment pathways of the Basilika Formation exposed in the Central Tertiary Basin of Svalbard. By means of geochemistry, SmNd isotopic signatures, and zircon UPb geochronology we investigate the characteristics of several bentonite layers contained in the Basilika Formation, as well as the provenance of the intercalated clastic sediments. Our data show that the volcanic ash layers of the Basilika Formation, which were diagenetically altered to bentonites, originate from alkaline continental-rift magmatism such as the last, explosive stages of the HALIP in North Greenland and the Canadian Arctic. The volcanic ash layers were deposited on Svalbard in a flat shelf environment with dominant sediment supply from the east. Dating of detrital zircons suggests that the detritus was derived from Siberian sources, primarily from the Verkhoyansk Fold-and-Thrust Belt, which would require transport over similar to 3000 km across the Arctic.
Bedrock landslides, by excavating deep below saprolite-rock interfaces, create conditions for weathering in which all mineral phases in a lithology are initially unweathered within landslide deposits. As a result, the most labile phases dominate the weathering immediately after mobilisation and during a transient period of depletion. This mode of dissolution can strongly alter the overall output of solutes from catchments and their contribution to global chemical cycles if landslide-derived material is retained in catchments for extended periods after mass wasting.
The Alanya Massif, which is located to the south of central Taurides in Turkey, presents a typical nappe pile consisting of thrust sheets with contrasting metamorphic histories. In two thrust sheets, Sugozu and GundogmuAY nappes, HP metamorphism under eclogite (550-567 A degrees C/14-18 kbar) and blueschist facies (435-480 A degrees C/11-13 kbar) conditions have been recognized, respectively. Whereas the rest of the Massif underwent MP metamorphism under greenschist to amphibolite facies (525-555 A degrees C/6.5-7.5 kbar) conditions. Eclogite facies metamorphism in Sugozu nappe, which consists of homogeneous garnet-glaucophane-phengite schists with eclogite lenses is dated at 84.8 +/- A 0.8, 84.7 +/- A 1.5 and 82 +/- A 3 Ma (Santonian-Campanian) by Ar-40/Ar-39 phengite, U/Pb zircon and rutile dating methods, respectively. Similarly, phengites in GundogmuAY nappe representing an accretionary complex yield 82-80 Ma (Campanian) ages for blueschist facies metamorphism. During the exhumation, the retrograde overprint of the HP units under greenschist-amphibolite facies conditions and tectonic juxtaposition with the Barrovian units occurred during Campanian (75-78 Ma). Petrological and geochronological data clearly indicate a similar Late Cretaceous tectonometamorphic evolution for both Alanya (84-75 Ma) and Bitlis (84-72 Ma) Massifs. They form part of a single continental sliver (Alanya-Bitlis microcontinent), which was rifted from the southern part of the Anatolide-Tauride platform. The P-T-t coherence between two Massifs suggests that both Massifs have been derived from the closure of the same ocean (Alanya-Bitlis Ocean) located to the south of the Anatolide-Tauride block by a northward subduction. The boundary separating the autochthonous Tauride platform to the north from both the Alanya and Bitlis Massifs to the south represents a suture zone, the Pamphylian-Alanya-Bitlis suture.
The global carbon cycle is closely linked to Earth’s climate. In the context of continuously unchecked anthropogenic CO₂ emissions, the importance of natural CO₂ bond and carbon storage is increasing. An important biogenic mechanism of natural atmospheric CO₂ drawdown is the photosynthetic carbon fixation in plants and the subsequent longterm deposition of plant detritus in sediments.
The main objective of this thesis is to identify factors that control mobilization and transport of plant organic matter (pOM) through rivers towards sedimentation basins. I investigated this aspect in the eastern Nepalese Arun Valley. The trans-Himalayan Arun River is characterized by a strong elevation gradient (205 − 8848 m asl) that is accompanied by strong changes in ecology and climate ranging from wet tropical conditions in the Himalayan forelad to high alpine tundra on the Tibetan Plateau. Therefore, the Arun is an excellent natural laboratory, allowing the investigation of the effect of vegetation cover, climate, and topography on plant organic matter mobilization and export in tributaries along the gradient.
Based on hydrogen isotope measurements of plant waxes sampled along the Arun River and its tributaries, I first developed a model that allows for an indirect quantification of pOM contributed to the mainsetm by the Arun’s tributaries. In order to determine the role of climatic and topographic parameters of sampled tributary catchments, I looked for significant statistical relations between the amount of tributary pOM export and tributary characteristics (e.g. catchment size, plant cover, annual precipitation or runoff, topographic measures). On one hand, I demonstrated that pOMsourced from the Arun is not uniformly derived from its entire catchment area. On the other, I showed that dense vegetation is a necessary, but not sufficient, criterion for high tributary pOM export. Instead, I identified erosion and rainfall and runoff as key factors controlling pOM sourcing in the Arun Valley. This finding is supported by terrestrial cosmogenic nuclide concentrations measured on river sands along the Arun and its tributaries in order to quantify catchment wide denudation rates. Highest denudation rates corresponded well with maximum pOM mobilization and export also suggesting the link between erosion and pOM sourcing.
The second part of this thesis focusses on the applicability of stable isotope records such as plant wax n-alkanes in sediment archives as qualitative and quantitative proxy for the variability of past Indian Summer Monsoon (ISM) strength. First, I determined how ISM strength affects the hydrogen and oxygen stable isotopic composition (reported as δD and δ18O values vs. Vienna Standard Mean Ocean Water) of precipitation in the Arun Valley and if this amount effect (Dansgaard, 1964) is strong enough to be recorded in potential paleo-ISM isotope proxies. Second, I investigated if potential isotope records across the Arun catchment reflect ISM strength dependent precipitation δD values only, or if the ISM isotope signal is superimposed by winter precipitation or glacial melt. Furthermore, I tested if δD values of plant waxes in fluvial deposits reflect δD values of environmental waters in the respective catchments.
I showed that surface water δD values in the Arun Valley and precipitation δD from south of the Himalaya both changed similarly during two consecutive years (2011 & 2012) with distinct ISM rainfall amounts (~20% less in 2012). In order to evaluate the effect of other water sources (Winter-Westerly precipitation, glacial melt) and evapotranspiration in the Arun Valley, I analysed satellite remote sensing data of rainfall distribution (TRMM 3B42V7), snow cover (MODIS MOD10C1), glacial coverage (GLIMSdatabase, Global Land Ice Measurements from Space), and evapotranspiration (MODIS MOD16A2). In addition to the predominant ISM in the entire catchment I found through stable isotope analysis of surface waters indications for a considerable amount of glacial melt derived from high altitude tributaries and the Tibetan Plateau. Remotely sensed snow cover data revealed that the upper portion of the Arun also receives considerable winter precipitation, but the effect of snow melt on the Arun Valley hydrology could not be evaluated as it takes place in early summer, several months prior to our sampling campaigns. However, I infer that plant wax records and other potential stable isotope proxy archives below the snowline are well-suited for qualitative, and potentially quantitative, reconstructions of past changes of ISM strength.
Understanding how compression affects the distribution of liquid water and gaseous oxygen in the polymer electrolyte membrane fuel cell gas diffusion layer (GDL) is vital for informing the design of improved porous materials for effective water management strategies. Pore networks extracted from synchrotron-based micro-computed tomography images of compressed GDLs were employed to simulate liquid water transport in GDL materials over a range of compression pressures. The oxygen transport resistance was predicted for each sample under dry and partially saturated conditions. A favorable GDL compression value for a preferred liquid water distribution and oxygen diffusion was found for Toray TGP-H-090 (10%), yet an optimum compression value was not recognized for SGL Sigracet 25BC. SGL Sigracet 25BC exhibited lower transport resistance values compared to Toray TGP-H-090, and this is attributed to the additional diffusion pathways provided by the microporous layer (MPL), an effect that is particularly significant under partially saturated conditions. (C) 2016 Elsevier B.V. All rights reserved.
Earthworms play a key role in regulating soil ecosystem functions and services. The small scale variability in earthworm abundance is often found to be very high, which is a problem for representative sampling of earthworm abundance at larger scales. In agricultural fields, soil tillage may influence both the average earthworm abundance as well as the spatial distribution of earthworms. Therefore we studied the abundance and spatial pattern of the different ecological earthworm types, i.e. endogeic, epigeic and anecic earthworms, in four agricultural fields differing in soil tillage (two fields with regular tillage and two fields with conservation tillage) and surrounding land use (other cropped fields or apple orchard and forest). To this aim we sampled earthworms on a total number of 430 plots (50 x 50 cm(2)) using a combination of extraction with mustard solution and hand sorting. The results exhibit large differences in average earthworm abundance between the four fields. Only one of the two fields with conservation tillage had a comparatively very high overall abundance of earthworms. Furthermore, we found a high spatial variability of earthworms within the field scale often exhibiting a patchy distribution. We detected a trend of decreasing earthworm abundances from the field border into the field for different earthworm groups on each of the fields. In three fields with low total earthworm abundance (and only very few epigeic earthworms) there was a short scale autocorrelation with ranges varying strongly for the endogeic earthworms (37.9 m, 62.6 m, and 85.2 m) compared to anecic earthworms (19.8 m, 22.8 m, and 27.4 m). In the field with high abundance, after trend removal, the variogram models for anecic and endogeic earthworms were rejected based on their negative explained variances. On this field, we found only a short scale autocorrelation for the epigeic earthworms with a range of 143 m. Based on these results it seems that ploughing alone cannot explain the differences in abundance and range of autocorrelation found on the four fields. The trend of strongly decreasing earthworm abundance from the field border into the field in the one field with high abundance does indicate that the field border or surrounding land use may also influence the recolonization of fields, but more research is required to provide further evidence for this hypothesis. Due to the very different patterns of earthworm distributions in the fields it remains difficult to recommend an optimal number and distance of samples to obtain a representative earthworm abundance for the field scale. (C) 2016 Elsevier B.V. All rights reserved.
The current view regarding the timing of regionally developed penetrative tectonic fabrics in sedimentary rocks is that their development postdates lithification of those rocks. In this case, fabric development is achieved by a number of deformation mechanisms, including grain rigid body rotation, crystal-plastic deformation, and pressure solution. The latter is believed to be the primary mechanism responsible for the domainal structure of cleavage in low-grade metamorphic rocks. In this study we combine field observations with strain studies to characterize considerable (>50%) Acadian crustal shortening in a Devonian clastic sedimentary sequence from southwest Ireland. Despite these high levels of shortening there is a marked absence of the domainal cleavage structure and intraclast deformation that are expected with this level of deformation. Fabrics in these rocks are predominantly a product of rigid body rotation and repacking of extraformational clasts during deformation of a clastic sedimentary sequence before lithification was complete.
Flood loss modeling is an important component for risk analyses and decision support in flood risk management. Commonly, flood loss models describe complex damaging processes by simple, deterministic approaches like depth-damage functions and are associated with large uncertainty. To improve flood loss estimation and to provide quantitative information about the uncertainty associated with loss modeling, a probabilistic, multivariable Bagging decision Tree Flood Loss Estimation MOdel (BT-FLEMO) for residential buildings was developed. The application of BT-FLEMO provides a probability distribution of estimated losses to residential buildings per municipality. BT-FLEMO was applied and validated at the mesoscale in 19 municipalities that were affected during the 2002 flood by the River Mulde in Saxony, Germany. Validation was undertaken on the one hand via a comparison with six deterministic loss models, including both depth-damage functions and multivariable models. On the other hand, the results were compared with official loss data. BT-FLEMO outperforms deterministic, univariable, and multivariable models with regard to model accuracy, although the prediction uncertainty remains high. An important advantage of BT-FLEMO is the quantification of prediction uncertainty. The probability distribution of loss estimates by BT-FLEMO well represents the variation range of loss estimates of the other models in the case study.
Rapidly uplifting coastlines are frequently associated with convergent tectonic boundaries, like subduction zones, which are repeatedly breached by giant megathrust earthquakes. The coastal relief along tectonically active realms is shaped by the effect of sea-level variations and heterogeneous patterns of permanent tectonic deformation, which are accumulated through several cycles of megathrust earthquakes. However, the correlation between earthquake deformation patterns and the sustained long-term segmentation of forearcs, particularly in Chile, remains poorly understood. Furthermore, the methods used to estimate permanent deformation from geomorphic markers, like marine terraces, have remained qualitative and are based on unrepeatable methods. This contrasts with the increasing resolution of digital elevation models, such as Light Detection and Ranging (LiDAR) and high-resolution bathymetric surveys.
Throughout this thesis I study permanent deformation in a holistic manner: from the methods to assess deformation rates, to the processes involved in its accumulation. My research focuses particularly on two aspects: Developing methodologies to assess permanent deformation using marine terraces, and comparing permanent deformation with seismic cycle deformation patterns under different spatial scales along the M8.8 Maule earthquake (2010) rupture zone. Two methods are developed to determine deformation rates from wave-built and wave-cut terraces respectively. I selected an archetypal example of a wave-built terrace at Santa Maria Island studying its stratigraphy and recognizing sequences of reoccupation events tied with eleven radiocarbon sample ages (14C ages). I developed a method to link patterns of reoccupation with sea-level proxies by iterating relative sea level curves for a range of uplift rates. I find the best fit between relative sea-level and the stratigraphic patterns for an uplift rate of 1.5 +- 0.3 m/ka.
A Graphical User Interface named TerraceM® was developed in Matlab®. This novel software tool determines shoreline angles in wave-cut terraces under different geomorphic scenarios. To validate the methods, I select test sites in areas of available high-resolution LiDAR topography along the Maule earthquake rupture zone and in California, USA. The software allows determining the 3D location of the shoreline angle, which is a proxy for the estimation of permanent deformation rates. The method is based on linear interpolations to define the paleo platform and cliff on swath profiles. The shoreline angle is then located by intersecting these interpolations. The
accuracy and precision of TerraceM® was tested by comparing its results with previous assessments, and through an experiment with students in a computer lab setting at the University
of Potsdam.
I combined the methods developed to analyze wave-built and wave-cut terraces to assess regional patterns of permanent deformation along the (2010) Maule earthquake rupture. Wave-built terraces are tied using 12 Infra Red Stimulated luminescence ages (IRSL ages) and shoreline angles in wave-cut terraces are estimated from 170 aligned swath profiles. The comparison of coseismic slip, interseismic coupling, and permanent deformation, leads to three areas of high permanent uplift, terrace warping, and sharp fault offsets. These three areas correlate with regions of high slip and low coupling, as well as with the spatial limit of at least eight historical megathrust ruptures (M8-9.5). I propose that the zones of upwarping at Arauco and Topocalma reflect changes in frictional properties of the megathrust, which result in discrete boundaries for the propagation of mega earthquakes.
To explore the application of geomorphic markers and quantitative morphology in offshore areas I performed a local study of patterns of permanent deformation inferred from hitherto unrecognized drowned shorelines at the Arauco Bay, at the southern part of the (2010) Maule earthquake rupture zone. A multidisciplinary approach, including morphometry, sedimentology, paleontology, 3D morphoscopy, and a landscape Evolution Model is used to recognize, map, and assess local rates and patterns of permanent deformation in submarine environments. Permanent deformation patterns are then reproduced using elastic models to assess deformation rates of an active submarine splay fault defined as Santa Maria Fault System. The best fit suggests a reverse structure with a slip rate of 3.7 m/ka for the last 30 ka. The register of land level changes during the earthquake cycle at Santa Maria Island suggest that most of the deformation may be accrued through splay fault reactivation during mega earthquakes, like the (2010) Maule event. Considering a recurrence time of 150 to 200 years, as determined from historical and geological observations, slip between 0.3 and 0.7 m per event would be required to account for the 3.7 m/ka millennial slip rate. However, if the SMFS slips only every ~1000 years, representing a few megathrust earthquakes, then a slip of ~3.5 m per event would be required to account for the long- term rate. Such event would be equivalent to a magnitude ~6.7 earthquake capable to generate a local tsunami.
The results of this thesis provide novel and fundamental information regarding the amount of permanent deformation accrued in the crust, and the mechanisms responsible for this accumulation at millennial time-scales along the M8.8 Maule earthquake (2010) rupture zone. Furthermore, the results of this thesis highlight the application of quantitative geomorphology and the use of repeatable methods to determine permanent deformation, improve the accuracy of marine terrace assessments, and estimates of vertical deformation rates in tectonically active coastal areas. This is vital information for adequate coastal-hazard assessments and to anticipate realistic earthquake and tsunami scenarios.
As field data on in-stream nitrate retention is scarce at catchment scales, this study aimed at quantifying net retention of nitrate within the entire river network of a fourth-order stream. For this purpose, a practical mass balance approach combined with a Lagrangian sampling scheme was applied and seasonally repeated to estimate daily in-stream net retention of nitrate for a 17.4 km long, agriculturally influenced, segment of the Steinlach River in southwestern Germany. This river segment represents approximately 70 % of the length of the main stem and about 32 % of the streambed area of the entire river network. Sampling days in spring and summer were biogeochemically more active than in autumn and winter. Results obtained for the main stem of Steinlach River were subsequently extrapolated to the stream network in the catchment. It was demonstrated that, for baseflow conditions in spring and summer, in-stream nitrate retention could sum up to a relevant term of the catchment’s nitrogen balance if the entire stream network was considered.
In contrast to recent advances in projecting sea levels, estimations about the economic impact of sea level rise are vague. Nonetheless, they are of great importance for policy making with regard to adaptation and greenhouse-gas mitigation. Since the damage is mainly caused by extreme events, we propose a stochastic framework to estimate the monetary losses from coastal floods in a confined region. For this purpose, we follow a Peak-over-Threshold approach employing a Poisson point process and the Generalised Pareto Distribution. By considering the effect of sea level rise as well as potential adaptation scenarios on the involved parameters, we are able to study the development of the annual damage. An application to the city of Copenhagen shows that a doubling of losses can be expected from a mean sea level increase of only 11 cm. In general, we find that for varying parameters the expected losses can be well approximated by one of three analytical expressions depending on the extreme value parameters. These findings reveal the complex interplay of the involved parameters and allow conclusions of fundamental relevance. For instance, we show that the damage typically increases faster than the sea level rise itself. This in turn can be of great importance for the assessment of sea level rise impacts on the global scale. Our results are accompanied by an assessment of uncertainty, which reflects the stochastic nature of extreme events. While the absolute value of uncertainty about the flood damage increases with rising mean sea levels, we find that it decreases in relation to the expected damage.
We report the first high-resolution (20-50 years) mid- to late Holocene pollen records from Lake Teletskoye, the largest lake in the Altai Mountains, in south-eastern West Siberia. Generally, the mid- to late Holocene (the last 4250 years) vegetation of the north-eastern Altai, as recorded in two studied sediment cores, is characterised by Siberian pine-spruce-fir forests that are similar to those of the present day. A relatively cool and dry interval with July temperatures lower than those of today occurred between 3.9 and 3.6 ka BP. The widespread distribution of open, steppe-like communities with Artemisia, Chenopodiaceae and Cyperaceae reflects maximum deforestation during this interval. After ca. 3.5 ka BP, the coniferous mountain taiga spread significantly, with maximum woody coverage and taiga biome scores between ca. 2.7 and 1.6 ka BP. This coincides well with the highest July temperature (approximately 1 degrees C higher than today) intervals. A short period of cooling about 13-1.4 ka BP could have been triggered by the increased volcanic activity recorded across the Northern Hemisphere. A new period of cooling started around 1100-1150 CE, with the minimum July temperatures occurring between 1450 and 1800 CE. (C) 2016 Elsevier B.V. All rights reserved.
We present a calibration-set based on modern pollen and satellite-based Advanced Very High Resolution Radiometer (AVHRR) observations of woody cover (including needleleaved, broadleaved and total tree cover) in eastern continental Asia, which shows good performance under cross-validation with the modern analogue technique (all the coefficients of determination between observed and predicted values are greater than 0.65). The calibration-set is used to reconstruct woody cover from a taxonomically harmonized and temporally standardized fossil pollen dataset (including 274 cores) with 500-year resolution over the last 22 kyr. The spatial range of forest has not noticeably changed in eastern continental Asia during the last 22 kyr, although woody cover has, especially at the margin of the eastern Tibetan Plateau and in the forest-steppe transition area of north-central China. Vegetation was sparse during the LGM in the present forested regions, but woody cover increased markedly at the beginning of the Bolling/Allerod period (B/A; ca. 14.5 ka BP) and again at the beginning of the Holocene (ca. 11.5 ka BP), and is related to the enhanced strength of the East Asian Summer Monsoon. Forest flourished in the mid Holocene (ca. 8 ka BP) possibly due to favourable climatic conditions. In contrast, cover was stable in southern China (high cover) and arid central Asia (very low cover) throughout the investigated period. Forest cover increased in the north-eastern part of China during the Holocene. Comparisons of these regional pollen-based results with simulated forest cover from runs of a global climate model (for 9, 6 and 0 ka BP (ECHAM5/JSBACH similar to 1.125 degrees spatial resolution)) reveal many similarities in temporal change. The Holocene woody cover history of eastern continental Asia is different from that of other regions, likely controlled by different climatic variables, i.e. moisture in eastern continental Asia; temperature in northern Eurasia and North America. (C) 2016 Elsevier Ltd. All rights reserved.
Abrupt climate changes and fluctuations over short time scales are superimposed on long-term climate changes. Understanding rapid climate fluctuations at the decadal time scale over the past millennium will enhance our understanding of patterns of climate variability and aid in forecasting climate changes in the future. In this study, climate changes on the southeastern Tibetan Plateau over the past millennium were determined from a 4.82-m-long sediment core from Basomtso Lake. At the centennial time scale, the Medieval Climate Anomaly (MCA), Little Ice Age (LIA) and Current Warm Period (CWP) are distinct in the Basomtso region. Rapid climate fluctuations inferred from five episodes with higher sediment input and likely warmer conditions, as well as seven episodes with lower sediment input and likely colder conditions, were well preserved in our record. These episodes with higher and lower sediment input are characterized by abrupt climate changes and short time durations. Spectral analysis indicates that the climate variations at the centennial scale on the southeastern Tibetan Plateau are influenced by solar activity during the past millennium.
Waterbodies such as lakes and ponds are abundant in vast Arctic landscapes and strongly affect the thermal state of the surrounding permafrost. In order to gain a better understanding of the impact of small-and medium-sized waterbodies on permafrost and the formation of thermokarst, a land surface model was developed that can represent the vertical and lateral thermal interactions between waterbodies and permafrost. The model was validated using temperature measurements from two typical waterbodies located within the Lena River delta in northern Siberia. Impact simulations were performed under current climate conditions as well as under a moderate and a strong climate-warming scenario. The performed simulations demonstrate that small waterbodies can rise the sediment surface temperature by more than 10 degrees C and accelerate permafrost thaw by a factor of between 4 and 5. Up to 70% of this additional heat flux into the ground was found to be dissipated into the surrounding permafrost by lateral ground heat flux in the case of small, shallow, and isolated waterbodies. Under moderate climate warming, the lateral heat flux was found to reduce permafrost degradation underneath waterbodies by a factor of 2. Under stronger climatic warming, however, the lateral heat flux was too small to prevent rapid permafrost degradation. The lateral heat flux was also found to strongly impede the formation of thermokarst. Despite this stabilizing effect, our simulations have demonstrated that underneath shallow waterbodies (<1 m), thermokarst initiation happens 30 to 40 years earlier than in simulations without preexisting waterbody.
Despite a large number of dated glacial landforms in the Himalaya, the ice extent during the global Last Glacial Maximum (LGM) from 19 to 23 ka is only known to first order. New cosmogenic Be-10 exposure ages from well-preserved glacially polished surfaces, combined with published data, and an improved production rate scaling model allow reconstruction of the LGM ice extent and subsequent deglaciation in the Chandra Valley of NW India. We show that a >1000 m thick valley glacier retreated >150 km within a few thousand years after the onset of LGM deglaciation. By comparing the recession of the Chandra Valley Glacier and other Himalayan glaciers with those of Northern and Southern Hemisphere glaciers, we demonstrate that post-LGM deglaciation was similar and nearly finished prior to the Bolling/Allerod interstadial. Our study supports the view that many Himalayan glaciers advanced during the LGM, likely in response to global variations in temperature.
Classification of clouds, cirrus, snow, shadows and clear sky areas is a crucial step in the pre-processing of optical remote sensing images and is a valuable input for their atmospheric correction. The Multi-Spectral Imager on board the Sentinel-2's of the Copernicus program offers optimized bands for this task and delivers unprecedented amounts of data regarding spatial sampling, global coverage, spectral coverage, and repetition rate. Efficient algorithms are needed to process, or possibly reprocess, those big amounts of data. Techniques based on top-of-atmosphere reflectance spectra for single-pixels without exploitation of external data or spatial context offer the largest potential for parallel data processing and highly optimized processing throughput. Such algorithms can be seen as a baseline for possible trade-offs in processing performance when the application of more sophisticated methods is discussed. We present several ready-to-use classification algorithms which are all based on a publicly available database of manually classified Sentinel-2A images. These algorithms are based on commonly used and newly developed machine learning techniques which drastically reduce the amount of time needed to update the algorithms when new images are added to the database. Several ready-to-use decision trees are presented which allow to correctly label about 91% of the spectra within a validation dataset. While decision trees are simple to implement and easy to understand, they offer only limited classification skill. It improves to 98% when the presented algorithm based on the classical Bayesian method is applied. This method has only recently been used for this task and shows excellent performance concerning classification skill and processing performance. A comparison of the presented algorithms with other commonly used techniques such as random forests, stochastic gradient descent, or support vector machines is also given. Especially random forests and support vector machines show similar classification skill as the classical Bayesian method.
The high rate GPS velocity determination technology which is based on the broadcast ephemeris and epoch differenced model can retrieve displacement of ground motion with the precision of a few centimetres to decimetres in real time. Moreover, the precision of the recovered displacement can be improved if the un-modelled errors such as broadcast ephemeris residuals, atmospheric residuals, multipath effects and high frequency noise are tackled more accurately. In this paper, we propose a method to improve the precision of the recovered displacement by appropriately making use of reference station corrections. For the reference stations, the coordinates are highly constrained to extract the error corrections that are to be broadcast via a communication link to the rover. After correcting the rover’s observations, some errors such as ephemeris residuals and atmospheric residuals are effectively eliminated or at least reduced. This improves the accuracy of the observations and thus enhances the reliability of the velocity estimation. The displacement can be recovered by integrating the estimated velocity after de-trending using a linear trend that is caused by the un-corrected residuals. The series of validation results in the experiment have shown that the displacement of the simulated motion can be real time recovered with a precision of 1–2 cm, and is thus applicable for real time monitoring of the ground motion.
Over the past decades, rapid and constant advances have motivated GNSS technology to approach the ability to monitor transient ground motions with mm to cm accuracy in real-time. As a result, the potential of using real-time GNSS for natural hazards prediction and early warning has been exploited intensively in recent years, e.g., landslides and volcanic eruptions monitoring. Of particular note, compared with traditional seismic instruments, GNSS does not saturate or tilt in terms of co-seismic displacement retrieving, which makes it especially valuable for earthquake and earthquake induced tsunami early warning. In this thesis, we focus on the application of real-time GNSS to fast seismic source inversion and tsunami early warning.
Firstly, we present a new approach to get precise co-seismic displacements using cost effective single-frequency receivers. As is well known, with regard to high precision positioning, the main obstacle for single-frequency GPS receiver is ionospheric delay. Considering that over a few minutes, the change of ionospheric delay is almost linear, we constructed a linear model for each satellite to predict ionospheric delay. The effectiveness of this method has been validated by an out-door experiment and 2011 Tohoku event, which confirms feasibility of using dense GPS networks for geo-hazard early warning at an affordable cost.
Secondly, we extended temporal point positioning from GPS-only to GPS/GLONASS and assessed the potential benefits of multi-GNSS for co-seismic displacement determination. Out-door experiments reveal that when observations are conducted in an adversary environment, adding a couple of GLONASS satellites could provide more reliable results. The case study of 2015 Illapel Mw 8.3 earthquake shows that the biases between co-seismic displacements derived from GPS-only and GPS/GLONASS vary from station to station, and could be up to 2 cm in horizontal direction and almost 3 cm in vertical direction. Furthermore, slips inverted from GPS/GLONASS co-seismic displacements using a layered crust structure on a curved plane are shallower and larger for the Illapel event.
Thirdly, we tested different inversion tools and discussed the uncertainties of using real-time GNSS for tsunami early warning. To be exact, centroid moment tensor inversion, uniform slip inversion using a single Okada fault and distributed slip inversion in layered crust on a curved plane were conducted using co-seismic displacements recorded during 2014 Pisagua earthquake. While the inversion results give similar magnitude and the rupture center, there are significant differences in depth, strike, dip and rake angles, which lead to different tsunami propagation scenarios. Even though, resulting tsunami forecasting along the Chilean coast is close to each other for all three models.
Finally, based on the fact that the positioning performance of BDS is now equivalent to GPS in Asia-Pacific area and Manila subduction zone has been identified as a zone of potential tsunami hazard, we suggested a conceptual BDS/GPS network for tsunami early warning in South China Sea. Numerical simulations with two earthquakes (Mw 8.0 and Mw 7.5) and induced tsunamis demonstrate the viability of this network. In addition, the advantage of BDS/GPS over a single GNSS system by source inversion grows with decreasing earthquake magnitudes.
The VIRTIS (Visible, Infrared and Thermal Imaging Spectrometer) instrument aboard the Rosetta spacecraft has performed extensive spectral mapping of the surface of comet 67P/Churyumov-Gerasimenko in the range 0.3-5 mu m. The reflectance spectra collected across the surface display a low reflectance factor over the whole spectral range, two spectral slopes in the visible and near-infrared ranges and a broad absorption band centered at 3.2 mu m. The first two of these characteristics are typical of dark small bodies of the Solar System and are difficult to interpret in terms of composition. Moreover, solar wind irradiation may modify the structure and composition of surface materials and there is no unequivocal interpretation of these spectra devoid of vibrational bands. To circumvent these problems, we consider the composition of cometary grains analyzed in the laboratory to constrain the nature of the cometary materials and consider results on surface rejuvenation and solar wind processing provided by the OSIRIS and ROSINA instruments, respectively. Our results lead to five main conclusions: (i) The low albedo of comet 67P/CG is accounted for by a dark refractory polyaromatic carbonaceous component mixed with opaque minerals. VIRTIS data do not provide direct insights into the nature of these opaque minerals. However, according to the composition of cometary grains analyzed in the laboratory, we infer that they consist of Fe-Ni alloys and FeS sulfides. (ii) A semi-volatile component, consisting of a complex mix of low weight molecular species not volatilized at T similar to 220 K, is likely a major carrier of the 3.2 p.m band. Water ice contributes significantly to this feature in the neck region but not in other regions of the comet. COOH in carboxylic acids is the only chemical group that encompasses the broad width of this feature. It appears as a highly plausible candidate along with the NH4+ ion. (iii) Photolytic/thermal residues, produced in the laboratory from interstellar ice analogs, are potentially good spectral analogs. (iv) No hydrated minerals were identified and our data support the lack of genetic links with the CI, CR and CM primitive chondrites. This concerns in particular the Orgueil chondrite, previously suspected to have been of cometary origin. (v) The comparison between fresh and aged terrains revealed no effect of solar wind irradiation on the 3.2 mu m band. This is consistent with the presence of efficient resurfacing processes such as dust transport from the interior to the surface, as revealed by the OSIRIS camera. (C) 2016 Elsevier Inc. All rights reserved.
Ice-rich permafrost coasts often undergo rapid erosion, which results in land loss and release of considerable amounts of sediment, organic carbon and nutrients, impacting the near-shore ecosystems. Because of the lack of volumetric erosion data, Arctic coastal erosion studies typically report on planimetric erosion. Our aim is to explore the relationship between planimetric and volumetric coastal erosion measurements and to update the coastal erosion rates on Herschel Island in the Canadian Arctic. We used high-resolution digital elevation models to compute sediment release and compare volumetric data to planimetric estimations of coastline movements digitized from satellite imagery. Our results show that volumetric erosion is locally less variable and likely corresponds better with environmental forcing than planimetric erosion. Average sediment release volumes are in the same range as sediment release volumes calculated from coastline movements combined with cliff height. However, the differences between these estimates are significant for small coastal sections. We attribute the differences between planimetric and volumetric coastal erosion measurements to mass wasting, which is abundant along the coasts of Herschel Island. The average recorded coastline retreat on Herschel Island was 0.68m a(-1) for the period 2000-2011. Erosion rates increased by more than 50% in comparison with the period 1970-2000, which is in accordance with a recently observed increase along the Alaskan Beaufort Sea. The estimated annual sediment release was 28.2 m(3) m(-1) with resulting fluxes of 590 kg C m(-1) and 104 kg N m(-1).
Geomorphic footprints of past large Himalayan earthquakes are elusive, although they are urgently needed for gauging and predicting recovery times of seismically perturbed mountain landscapes. We present evidence of catastrophic valley infill following at least three medieval earthquakes in the Nepal Himalaya. Radiocarbon dates from peat beds, plant macrofossils, and humic silts in fine-grained tributary sediments near Pokhara, Nepal’s second-largest city, match the timing of nearby M > 8 earthquakes in ~1100, 1255, and 1344 C.E. The upstream dip of tributary valley fills and x-ray fluorescence spectrometry of their provenance rule out local sources. Instead, geomorphic and sedimentary evidence is consistent with catastrophic fluvial aggradation and debris flows that had plugged several tributaries with tens of meters of calcareous sediment from a Higher Himalayan source >60 kilometers away.
The northern Tien Shan of Kyrgyzstan and Kazakhstan has been affected by a series of major earthquakes in the late 19th and early 20th centuries. To assess the significance of such a pulse of strain release in a continental interior, it is important to analyze and quantify strain release over multiple time scales. We have undertaken paleoseismological investigations at two geomorphically distinct sites (Panfilovkoe and Rot Front) near the Kyrgyz capital Bishkek. Although located near the historic epicenters, both sites were not affected by these earthquakes. Trenching was accompanied by dating stratigraphy and offset surfaces using luminescence, radiocarbon, and Be-10 terrestrial cosmogenic nuclide methods. At Rot Front, trenching of a small scarp did not reveal evidence for surface rupture during the last 5000 years. The scarp rather resembles an extensive debris-flow lobe. At Panfilovkoe, we estimate a Late Pleistocene minimum slip rate of 0.2 +/- 0.1 mm/a, averaged over at least two, probably three earthquake cycles. Dip-slip reverse motion along segmented, moderately steep faults resulted in hanging wall collapse scarps during different events. The most recent earthquake occurred around 3.6 +/- 1.3 kyr ago (1 sigma), with dip-slip offsets between 1.2 and 1.4 m. We calculate a probabilistic paleomagnitude to be between 6.7 and 7.2, which is in agreement with regional data from the Kyrgyz range. The morphotectonic signals in the northern Tien Shan are a prime example of deformation in a tectonically active intracontinental mountain belt and as such can help understand the longer-term coevolution of topography and seismogenic processes in similar structural settings worldwide.
The onset of modern central Asian atmospheric circulation is traditionally linked to the interplay of surface uplift of the Mongolian and Tibetan-Himalayan orogens, retreat of the Paratethys sea from central Asia and Cenozoic global cooling. Although the role of these players has not yet been unravelled, the vast dust deposits of central China support the presence of arid conditions and modern atmospheric pathways for the last 25 million years (Myr). Here, we present provenance data from older (42-33 Myr) dust deposits, at a time when the Tibetan Plateau was less developed, the Paratethys sea still present in central Asia and atmospheric pCO(2) much higher. Our results show that dust sources and near-surface atmospheric circulation have changed little since at least 42 Myr. Our findings indicate that the locus of central Asian high pressures and concurrent aridity is a resilient feature only modulated by mountain building, global cooling and sea retreat.
Widespread flooding in June 2013 caused damage costs of €6 to 8 billion in Germany, and awoke many memories of the floods in August 2002, which resulted in total damage of €11.6 billion and hence was the most expensive natural hazard event in Germany up to now. The event of 2002 does, however, also mark a reorientation toward an integrated flood risk management system in Germany. Therefore, the flood of 2013 offered the opportunity to review how the measures that politics, administration, and civil society have implemented since 2002 helped to cope with the flood and what still needs to be done to achieve effective and more integrated flood risk management. The review highlights considerable improvements on many levels, in particular (1) an increased consideration of flood hazards in spatial planning and urban development, (2) comprehensive property-level mitigation and preparedness measures, (3) more effective flood warnings and improved coordination of disaster response, and (4) a more targeted maintenance of flood defense systems. In 2013, this led to more effective flood management and to a reduction of damage. Nevertheless, important aspects remain unclear and need to be clarified. This particularly holds for balanced and coordinated strategies for reducing and overcoming the impacts of flooding in large catchments, cross-border and interdisciplinary cooperation, the role of the general public in the different phases of flood risk management, as well as a transparent risk transfer system. Recurring flood events reveal that flood risk management is a continuous task. Hence, risk drivers, such as climate change, land-use changes, economic developments, or demographic change and the resultant risks must be investigated at regular intervals, and risk reduction strategies and processes must be reassessed as well as adapted and implemented in a dialogue with all stakeholders.