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A new sedimentary sequence from Lago di Venere on Pantelleria Island, located in the Strait of Sicily between Tunisia and Sicily was recovered. The lake is located in the coastal infra-Mediterranean vegetation belt at 2 m a.s.l. Pollen, charcoal and sedimentological analyses are used to explore linkages among vegetation, fire and climate at a decadal scale over the past 1200 years. A dry period from ad 800 to 1000 that corresponds to the Medieval Warm Period' (WMP) is inferred from sedimentological analysis. The high content of carbonate recorded in this period suggests a dry phase, when the ratio of evaporation/precipitation was high. During this period the island was dominated by thermophilous and drought-tolerant taxa, such as Quercus ilex, Olea, Pistacia and Juniperus. A marked shift in the sediment properties is recorded at ad 1000, when carbonate content became very low suggesting wetter conditions until ad 1850-1900. Broadly, this period coincides with the Little Ice Age' (LIA), which was characterized by wetter and colder conditions in Europe. During this time rather mesic conifers (i.e. Pinus pinaster), shrubs and herbs (e.g. Erica arborea and Selaginella denticulata) expanded, whereas more drought-adapted species (e.g. Q. ilex) declined. Charcoal data suggest enhanced fire activity during the LIA probably as a consequence of anthropogenic burning and/or more flammable fuel (e.g. resinous Pinus biomass). The last century was characterized by a shift to high carbonate content, indicating a change towards drier conditions, and re-expansion of Q. ilex and Olea. The post-LIA warming is in agreement with historical documents and meteorological time series. Vegetation dynamics were co-determined by agricultural activities on the island. Anthropogenic indicators (e.g. Cerealia-type, Sporormiella) reveal the importance of crops and grazing on the island. Our pollen data suggest that extensive logging caused the local extinction of deciduous Quercus pubescens around ad1750.
Based on a numerical model of the Northeast German Basin (NEGB), we investigate the sensitivity of the calculated thermal field as resulting from heat conduction, forced and free convection in response to consecutive horizontal and vertical mesh refinements. Our results suggest that computational findings are more sensitive to consecutive horizontal mesh refinements than to changes in the vertical resolution. In addition, the degree of mesh sensitivity depends strongly on the type of the process being investigated, whether heat conduction, forced convection or free thermal convection represents the active heat driver. In this regard, heat conduction exhibits to be relative robust to imposed changes in the spatial discretization. A systematic mesh sensitivity is observed in areas where forced convection promotes an effective role in shorten the background conductive thermal field. In contrast, free thermal convection is to be regarded as the most sensitive heat transport process as demonstrated by non-systematic changes in the temperature field with respect to imposed changes in the model resolution.
Reliable hydrological monitoring is the basis for sound water management in drained wetlands. Since statistical methods cannot be employed for unobserved or sparsely monitored areas, the primary design (first set-up) may be arbitrary in most instances. The objective of this paper is therefore to provide a guideline for designing the initial hydrological monitoring network. A scheme is developed that handles different parts of monitoring and hydrometry in wetlands, focusing on the positioning of surface water and groundwater gauges. For placement of the former, control units are used which correspond to areas whose water levels can be regulated separately. The latter are arranged depending on hydrological response units, defined by combinations of soil type and land use, and the chosen surface water monitoring sites. A practical application of the approach is shown for an investigation area in the Spreewald region in north-east Germany. The presented scheme leaves a certain degree of freedom to its user, allowing the inclusion of expert knowledge or special concerns. Based on easily obtainable data, the developed hydrological network serves as a first step in the iterative procedure of monitoring network optimisation. Copyright (c) 2013 John Wiley & Sons, Ltd.
A total of 271 pollen records were selected from a large collection of both raw and digitized pollen spectra from eastern continental Asia (70 degrees-135 degrees E and 18 degrees-55 degrees N). Following pollen percentage recalculations, taxonomic homogenization, and age-depth model revision, the pollen spectra were interpolated at a 500-year resolution and a taxonomically harmonized and temporally standardized fossil pollen dataset established with 226 pollen taxa, covering the last 22 cal lea. Of the 271 pollen records, 85% were published since 1990, with reliable chronologies and high temporal resolutions; of these, 50% have raw data with complete pollen assemblages, ensuring the quality of this dataset The pollen records available for each 500-year time slice are well distributed over all main vegetation types and climatic zones of the study area, making their pollen spectra suitable for paleovegetation and paleoclimate research. Such a dataset can be used as an example for the development of similar datasets for other regions of the world.
The Pleistocene archeological record in East Africa has revealed unusual accumulations of Acheulean handaxes at prehistoric sites. In particular, there has been intensive debate concerning whether the artifact accumulation at the Middle Pleistocene Olorgesailie (Southern Kenya Rift) and Kariandusi (Central Kenya Rift) sites were a result of fluvial reworking or of in situ deposition by hominids. We used a two-step approach to test the hypothesis of fluvial reworking. Firstly, the behavior of handaxes in water currents was investigated in a current flume and the flow threshold required to reorientate the handaxes was determined. The results of these experiments suggested that, in relatively high energy and non-steady flow conditions, handaxes will reorientate themselves perpendicular to the current direction. Secondly, an automated image analysis routine was developed and applied to archeological plans from three Acheulean sites, two at Olorgesailie and one at Kariandusi, in order to determine the orientations of the handaxes. A Rayleigh test was then applied to the orientation data to test for a preferred orientation. The results revealed that the handaxes at the Upper Kariandusi Site and the Olorgesailie Main Site Mid Trench had a preferential orientation, suggesting reworking by a paleocurrent. The handaxes from the Olorgesailie Main Site H/6A, however, appeared to be randomly oriented and in situ deposition by the producers therefore remains a possibility.
This study aims to establish, evaluate, and apply a modern pollen-climate transfer function from the transition zone between arctic tundra and light-needled taiga in Arctic Siberia. Lacustrine samples (n = 96) from the northern Siberian lowlands of Yakutia were collected along four north-to-south transects crossing the arctic forest line. Samples span a broad temperature and precipitation gradient (mean July temperature, T-July: 7.5-18.7 degrees C; mean annual precipitation, P-ann: 114-315 mm/yr). Redundancy analyses are used to examine the relationship between the modern pollen signal and corresponding vegetation types and climate. Performance of transfer functions for T-July and P-ann were cross-validated and tested for spatial autocorrelation effects. The root mean square errors of prediction are 1.67 degrees C for T-July and 40 mm/yr for P-ann. A climate reconstruction based on fossil pollen spectra from a Siberian Arctic lake sediment core spanning the Holocene yielded cold conditions for the Late Glacial (1-2 degrees C below present T-July). Warm and moist conditions were reconstructed for the early to mid Holocene (2 degrees C higher T-July than present), and climate conditions similar to modern ones were reconstructed for the last 4000 years. In conclusion, our modern pollen data set fills the gap of existing regional calibration sets with regard to the underrepresented Siberian tundra-taiga transition zone. The Holocene climate reconstruction indicates that the temperature deviation from modern values was only moderate despite the assumed Arctic sensitivity to present climate change.
Pseudotachylyte veins frequently associated with mylonites and ultramylonites occur within migmatitic paragneisses, metamonzodiorites, as well as felsic and mafic granulites at the base of the section of the Hercynian lower crust exposed in Calabria (Southern Italy). The crustal section is tectonically superposed on lower grade units. Ultramylonites and pseudotachylytes are particularly well developed in migmatitic paragneisses, whereas sparse fault-related pseudotachylytes and thin mylonite/ultramylonite bands occur in granulite-facies rocks. The presence of sillimanite and clinopyroxene in ultramylonites and mylonites indicates that relatively high-temperature conditions preceded the formation of pseudotachylytes. We have analysed pseudotachylytes from different rock types to ascertain their deep crustal origin and to better understand the relationships between brittle and ductile processes during deformation of the deeper crust. Different protoliths were selected to test how lithology controls pseudotachylyte composition and textures. In migmatites and felsic granulites, euhedral or cauliflower-shaped garnets directly crystallized from pseudotachylyte melts of near andesitic composition. This indicates that pseudotachylytes originated at deep crustal conditions (> 0.75 GPa). In mafic protoliths, quenched needle-to-feather-shaped high-alumina orthopyroxene occurs in contact with newly crystallized plagioclase. The pyroxene crystallizes in garnet-free and garnet-bearing veins. The simultaneous growth of orthopyroxene and plagioclase as well as almandine, suggests lower crustal origin, with pressures in excess of 0.85 GPa. The existence of melts of different composition in the same vein indicates the stepwise, non-equilibrium conditions of frictional melting. Melt formed and intruded into pre-existing anisotropies. In mafic granulites, brittle faulting is localized in a previously formed thin high-temperature mylonite bands. migmatitic gneisses are deformed into ultramylonite domains characterized by s-c fabric. Small grain size and fluids lowered the effective stress on the c planes favouring a seismic event and the consequent melt generation. Microstructures and ductile deformation of pseudotachylytes suggest continuous ductile flow punctuated by episodes of high-strain rate, leading to seismic events and melting.
Environmental parameters such as rainfall, temperature and relative humidity can affect the composition of higher plant leaf wax. The abundance and distribution of leaf wax biomarkers, such as long chain n-alkanes, in sedimentary archives have therefore been proposed as proxies reflecting climate change. However, a robust palaeoclimatic interpretation requires a thorough understanding of how environmental changes affect leaf wax n-alkane distributions in living plants. We have analysed the concentration and chain length distribution of leaf wax n-alkanes in Acacia and Eucalyptus species along a 1500 km climatic gradient in northern Australia that ranges from subtropical to arid. We show that aridity affected the concentration and distribution of n-alkanes for plants in both genera. For both Acacia and Eucalyptus n-alkane concentration increased by a factor of ten to the dry centre of Australia, reflecting the purpose of the wax in preventing water loss from the leaf. Furthermore, Acacian-alkanes decreased in average chain length (ACL) towards the arid centre of Australia, whereas Eucalyptus ACL increased under arid conditions. Our observations demonstrate that n-alkane concentration and distribution in leaf wax are sensitive to hydroclimatic conditions. These parameters could therefore potentially be employed in palaeorecords to estimate past environmental change. However, our finding of a distinct response of n-alkane ACL values to hydrological changes in different taxa also implies that the often assumed increase in ACL under drier conditions is not a robust feature for all plant species and genera and as such additional information about the prevalent vegetation are required when ACL values are used as a palaeoclimate proxy.
Convexities in the longitudinal profiles of actively incising rivers are typically considered to represent the morphologic signal of a transient response to external perturbations in tectonic or climatic forcing. Distinguishing such knickzones from those that may be anchored to the channel network by spatial variations in rock uplift, however, can be challenging. Here, we combine stream profile analysis, Be-10 watershed-averaged erosion rates, and numerical modeling of stream profile evolution to evaluate whether knickzones in the Abukuma massif of northeast Japan represent a temporal or spatial change in rock uplift rate in relation to forearc shortening. Knickzones in channels that drain the eastern flank of the Abukuma massif are characterized by breaks in slope-area scaling and separate low-gradient, alluvial upper-channel segments from high-gradient, deeply-incised lower channel segments. Average erosion rates inferred from Be-10 concentrations in modern sediment below knickzones exceed erosion rates above knickzones by 20-50%. Although profile convexities could be interpreted as a transient response to an increase in rock uplift rate associated with slip on the range-bounding fault, geologic constraints on the initiation of fault slip and the magnitude of displacement cannot be reconciled with a recent, spatially uniform increase in slip rate. Rather, we find that knickzone position, stream profile gradients, and basin averaged erosion rates are best explained by a relatively abrupt spatial increase in uplift rate localized above a flat-ramp transition in the fault system. These analyses highlight the importance of considering spatially non-uniform uplift in the interpretation of stream profile evolution and demonstrate that the adjustment of river profiles to fault displacement can provide constraints on fault geometry in actively eroding landscapes. (C) 2013 Elsevier B.V. All rights reserved.
We review the geodynamic evolution of the Aegean-Anatolia region and discuss strain localisation there over geological times. From Late Eocene to Present, crustal deformation in the Aegean backarc has localised progressively during slab retreat. Extension started with the formation of the Rhodope Metamorphic Core Complex (Eocene) and migrated to the Cyclades and the northern Menderes Massif (Oligocene and Miocene), accommodated by crustal-scale detachments and a first series of core complexes (MCCs). Extension then localised in Western Turkey, the Corinth Rift and the external Hellenic arc after Messinian times, while the North Anatolian Fault penetrated the Aegean Sea. Through time the direction and style of extension have not changed significantly except in terms of localisation. The contributions of progressive slab retreat and tearing, basal drag, extrusion tectonics and tectonic inheritance are discussed and we favour a model (I) where slab retreat is the main driving engine, (2) successive slab tearing episodes are the main causes of this stepwise strain localisation and (3) the inherited heterogeneity of the crust is a major factor for localising detachments. The continental crust has an inherited strong heterogeneity and crustal-scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation. The dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate. Successive slab ruptures from the Middle Miocene to the late Miocene have isolated a narrow strip of lithosphere, still attached to the African lithosphere below Crete. The formation of the North Anatolian Fault is partly a consequence of this evolution. The extrusion of Anatolia and the Aegean extension are partly driven from below (asthenospheric flow) and from above (extrusion of a lid of rigid crust).
The occurrence of neritic microbial carbonates is often related to ecological refuges, where grazers and other competitors are reduced by environmental conditions, or to post-extinction events (e.g. in the Late Devonian, Early Triassic). Here, we present evidence for Middle Jurassic (Bajocian) microbial mounds formed in the normal marine, shallow neritic setting of an inner, ramp system from the High Atlas of Morocco. The microbial mounds are embedded in cross-bedded oolitic facies. Individual mounds show low relief domal geometries (up to 3 m high and 4.5 m across), but occasionally a second generation of mounds exhibits tabular geometries (<1 m high). The domes are circular in plan view and have intact tops, lacking evidence of current influence on mound preferred growth direction or distribution patterns, or truncation. The mound fades consists almost entirely of non-laminated, micritic thrombolites with branching morphologies and fine-grained, clotted and peloidal fabrics. Normal marine biota are present but infrequent. Several lines of evidence document that microbial mound growth alternates with time intervals of active ooid shoal deposition. This notion is of general significance when compared with modern Bahamian microbialites that co-exist with active sub-aquatic dunes. Furthermore, the lack of detailed studies of Middle Jurassic, normal marine shallow neritic microbial mounds adds a strong motivation for the present study. Specifically, Bajocian mounds formed on a firmground substratum during transgressive phases under condensed sedimentation. Furthermore, a transient increase in nutrient supply in the prevailing mesotrophic setting, as suggested by the heterotrophic-dominated biota, may have controlled microbial mound stages.
Agricultural soils have a high potential for sequestration of atmospheric carbon due to their volume and several promising management options. However, there is a remarkable lack of information about the status quo of organic carbon in agricultural soils. In this study a comprehensive data set of 384 cropland soils and 333 grassland soils within the state of Bavaria in southeast Germany was analyzed in order to provide representative information on total amount, regional distribution and driving parameters of soil organic carbon (SOC) and nitrogen (N) in agricultural soils of central Europe. The results showed that grassland soils stored higher amounts of SOC (11.8 kg m(-2)) and N (0.92 kg m(-2)) than cropland soils (9.0 and 0.66 kg m(-2), respectively) due to moisture-induced accumulation of soil organic matter (SOM) in B horizons. Surprisingly, no distinct differences were found for the A horizons since tillage led to a relocation of SOM with depth in cropland soils. Statistical analyses of driving factors for SOM storage revealed soil moisture, represented by the topographic wetness index (TWI), as the most important parameter for both cropland and grassland soils. Climate effects (mean annual temperature and precipitation) were of minor importance in agricultural soils because management options counteracted them to a certain extent, particularly in cropland soils. The distribution of SOC and N stocks within Bavaria based on agricultural regions confirmed the importance of soil moisture since the highest cropland SOC and N stocks were found for tertiary hills and loess regions, which exhibited large areas with potentially high soil moisture content in extant floodplains. Grassland soils showed the highest accumulation of SOC and N in the Alps and Pre-Alps as a result of low temperatures, high amounts of precipitation and high soil moisture content in areas of glacial denudation. Soil class was identified as a further driving parameter for SOC and N storage in cropland soils. In total, cropland and grassland soils in Bavaria store 242 and 134 Mt SOC as well as 19 and 12 Mt N down to a soil depth of 1 m or the parent material, respectively.
In this paper a change-point detection method is proposed by extending the singular spectrum transformation (SST) developed as one of the capabilities of singular spectrum analysis (SSA). The method uncovers change points related with trends and periodicities. The potential of the proposed method is demonstrated by analysing simple model time series including linear functions and sine functions as well as real world data (precipitation data in Kenya). A statistical test of the results is proposed based on a Monte Carlo simulation with surrogate methods. As a result, the successful estimation of change points as inherent properties in the representative time series of both trend and harmonics is shown. With regards to the application, we find change points in the precipitation data of Kenyan towns (Nakuru, Naivasha, Narok, and Kisumu) which coincide with the variability of the Indian Ocean Dipole (IOD) suggesting its impact of extreme climate in East Africa.
In probabilistic seismic-hazard analysis, epistemic uncertainties are commonly treated within a logic-tree framework in which the branch weights express the degree of belief of an expert in a set of models. For the calculation of the distribution of hazard curves, these branch weights represent subjective probabilities. A major challenge for experts is to provide logically consistent weight estimates (in the sense of Kolmogorovs axioms), to be aware of the multitude of heuristics, and to minimize the biases which affect human judgment under uncertainty. We introduce a platform-independent, interactive program enabling us to quantify, elicit, and transfer expert knowledge into a set of subjective probabilities by applying experimental design theory, following the approach of Curtis and Wood (2004). Instead of determining the set of probabilities for all models in a single step, the computer-driven elicitation process is performed as a sequence of evaluations of relative weights for small subsets of models. From these, the probabilities for the whole model set are determined as a solution of an optimization problem. The result of this process is a set of logically consistent probabilities together with a measure of confidence determined from the amount of conflicting information which is provided by the expert during the relative weighting process. We experiment with different scenarios simulating likely expert behaviors in the context of knowledge elicitation and show the impact this has on the results. The overall aim is to provide a smart elicitation technique, and our findings serve as a guide for practical applications.
Scarcity of hydrological data, especially streamflow discharge and groundwater level series, restricts the understanding of channel transmission losses (TL) in drylands. Furthermore, the lack of information on spatial river dynamics encompasses high uncertainty on TL analysis in large rivers. The objective of this study was to combine the information from streamflow and groundwater level series with multi-temporal satellite data to derive a hydrological concept of TL for a reach of the Middle Jaguaribe River (MJR) in semi-arid north-eastern Brazil. Based on this analysis, we proposed strategies for its modelling and simulation. TL take place in an alluvium, where river and groundwater can be considered to be hydraulically connected. Most losses certainly infiltrated only through streambed and levees and not through the flood plains, as could be shown by satellite image analysis. TL events whose input river flows were smaller than a threshold did not reach the outlet of the MJR. TL events whose input flows were higher than this threshold reached the outlet losing on average 30% of their input. During the dry seasons (DS) and at the beginning of rainy seasons (DS/BRS), no river flow is expected for pre-events, and events have vertical infiltration into the alluvium. At the middle and the end of the rainy seasons (MRS/ERS), river flow sustained by base flow occurs before/after events, and lateral infiltration into the alluvium plays a major role. Thus, the MJR shifts from being a losing river at DS/BRS to become a losing/gaining (mostly losing) river at MRS/ERS. A model of this system has to include the coupling of river and groundwater flow processes linked by a leakage approach.
Seismicity induced by coal mining in the Ruhr region, Germany, has been monitored continuously over the last 25 yr. In 2006, a dense temporary network (HAMNET) was deployed to locally monitor seismicity induced by longwall mining close to the town of Hamm. Between 2006 July and 2007 July, more than 7000 events with magnitudes M-L from -1.7 to 2.0 were detected. The spatiotemporal distribution of seismicity shows high correlation with the mining activity. In order to monitor rupture processes, we set up an automated source inversion routine and successfully perform double couple and full moment tensor (MT) inversions for more than 1000 events with magnitudes above M-L -0.5. The source inversion is based on a full waveform approach, both in the frequency and in the time domain, providing information about the centroid location, focal mechanism, scalar moment and full MT. Inversion results indicate a strong dominance of normal faulting focal mechanisms, with a steeper plane and a subhorizontal one. Fault planes are oriented parallel to the mining stopes. We classify the focal mechanisms based on their orientation and observe different frequency-magnitude distributions for families of events with different focal mechanisms; the overall frequency-magnitude distribution is not fitting the Gutenberg-Richter relation. Full MTs indicate that non-negligible opening tensile components accompanied normal faulting source mechanisms. Finally, extended source models are investigated for largest events. Results suggest that the rupture processes mostly occurred along the subvertical planes.
Automated seismic event location by travel-time stacking an application to mining induced seismicity
(2013)
Die Ziele der Energiewende sind ehrgeizig. Der Vortrag zeigt, welche Nutzungsoptionen der Untergrund bietet - z.B. geothermische Energiegewinnung oder geologische Speicherung. Für eine gesellschaftsweite, sachliche Diskussion werden konkrete Zahlen nicht nur zu den Chancen, sondern auch zu den Risiken benötigt.
In undisturbed tropical montane rainforests massive organic layers accommodate the majority of roots and only a small fraction of roots penetrate the mineral soil. We investigated the contribution of vegetation to slope stability in such environments by modifying a standard model for slope stability to include an organic layer with distinct mechanical properties. The importance of individual model parameters was evaluated using detailed measurements of soil and vegetation properties to reproduce the observed depth of 11 shallow landslides in the Andes of southern Ecuador. By distinguishing mineral soil, organic layer and above-ground biomass, it is shown that in this environment vegetation provides a destabilizing effect mainly due to its contribution to the mass of the organic layer (up to 973 t ha-1 under wet conditions). Sensitivity analysis shows that the destabilizing effect of the mass of soil and vegetation can only be effective on slopes steeper than 37.9 degrees. This situation applies to 36% of the study area. Thus, on the steep slopes of this megadiverse ecosystem, the mass of the growing forest promotes landsliding, which in turn promotes a new cycle of succession. This feedback mechanism is worth consideration in further investigations of the impact of landslides on plant diversity in similar environments.
The Upper Cretaceous shallow-water carbonates of the Pyrenean Basin (NE Spain) host rich and diverse larger foraminiferal associations which witness the recovery of this group of protozoans after the dramatic extinction of the Cenomanian-Turonian boundary interval. In this paper a new, large discoidal porcelaneous foraminifer, Broeckina gassoensis sp. nov., is described from the middle Coniacian shallow-water deposits of the Collada Gasso Formation, in the Boixols Thrust Sheet. This is the first complex porcelaneous larger foraminifer of the Late Cretaceous global community maturation cycle recorded in the Pyrenean bioprovince. It differs from the late Santonian-early Campanian B. dufrenoyi for its smaller size in A and B generations and the less developed endoskeleton, which shows short septula. Broeckina gassoensis sp. nov. has been widely employed as a stratigraphic marker in the regional geological literature, under the name of "Broeckina", but its age was so far controversial. Its middle Coniacian age (lowermost part of the Peroniceras tridorsatum ammonite zone), established in this paper by strontium isotope stratigraphy, indicates that it took about 5 My after the Cenomanian-Turonian boundary crisis to re-evolve the complex test architecture of larger foraminifera, which is functional to their relation with photosymbiotic algae and K-strategy.
Surface lake sediments, 28 from Hoh Xil, 24 from northeastern China, 99 from Lake Bosten, 31 from Ulungur and 26 from Heihai were collected to determine C-13 and O-18 values. Considering the impact factors, conductivity, alkalinity, pH, TOC, C/N and carbonate-content in the sediments, Cl, P, S, and metal element ratios of Mg/Ca, Sr/Ca, Fe/Mn of bulk sediments as environmental variables enable evaluation of their influences on C-13 and O-18 using principal component analysis (PCA) method. The closure and residence time of lakes can influence the correlation between C-13 and O-18. Lake water will change from fresh to brackish with increasing reduction and eutrophication effects. Mg/Ca in the bulk sediment indicates the characteristic of residence time, Sr/Ca and Fe/Mn infer the salinity of lakes. Carbonate formation processes and types can influence the C-13-O-18 correlation. O-18 will be heavier from Mg-calcite and aragonite formed in a high-salinity water body than calcite formed in freshwater conditions. When carbonate content is less than 30%, there is no relationship with either C-13 or O-18, and also none between C-13 and O-18. More than 30%, carbonate content, however, co-varies highly to C-13 and O-18, and there is also a high correlation between C-13 and O-18. Vegetation conditions and primary productivity of lakes can influence the characteristics of C-13 and O-18, and their co-variance. Total organic matter content (TOC) in the sediments is higher with more terrestrial and submerged plants infilling. In northeastern and northwestern China, when organic matter in the lake sediments comes from endogenous floating organisms and algae, the C-13 value is high. C-13 is in the range of -4%o to 0 parts per thousand when organic matter comes mainly from floating organisms (C/N<6); in the range of -4 parts per thousand to 8 parts per thousand when organic matter comes from diatoms (C/N=6 to 8); and -8 parts per thousand to -4 parts per thousand when organic matter comes from aquatic and terrestrial plants (C/N>8).
Natural and human-induced erosion supplies high amounts of soil organic carbon (OC) to terrestrial drainage networks. Yet OC fluxes in rivers were considered in global budgets only recently. Modern estimates of annual carbon burial in inland river sediments of 0.6 Gt C, or 22% of C transferred from terrestrial ecosystems to river channels, consider only lakes and reservoirs and disregard any long-term carbon burial in hillslope or floodplain sediments. Here we present the first assessment of sediment-bound OC storage in Central Europe from a synthesis of similar to 1500 Holocene hillslope and floodplain sedimentary archives. We show that sediment storage increases with drainage-basin size due to more extensive floodplains in larger river basins. However, hillslopes retain hitherto unrecognized high amounts of eroded soils at the scale of large river basins such that average agricultural erosion rates during the Holocene would have been at least twice as high as reported previously. This anthropogenic hillslope sediment storage exceeds floodplain storage in drainage basins <10(5) km(2), challenging the notion that floodplains are the dominant sedimentary sinks. In terms of carbon burial, OC concentrations in floodplains exceed those on hillslopes, and net OC accumulation rates in floodplains (0.70.2 g C m(-2)a(-1)) surpass those on hillslopes (0.40.1 g C m(-2)a(-1)) over the last 7500 years. We conclude that carbon burial in floodplains and on hillslopes in Central Europe exceeds terrestrial carbon storage in lakes and reservoirs by at least 2 orders of magnitude and should thus be considered in continental carbon budgets.
Changes in rainfall interception along a secondary forest succession gradient in lowland Panama
(2013)
Secondary forests are rapidly expanding in tropical regions. Yet, despite the importance of understanding the hydrological consequences of land-cover dynamics, the relationship between forest succession and canopy interception is poorly understood. This lack of knowledge is unfortunate because rainfall interception plays an important role in regional water cycles and needs to be quantified for many modeling purposes. To help close this knowledge gap, we designed a throughfall monitoring study along a secondary succession gradient in a tropical forest region of Panama. The investigated gradient comprised 20 forest patches 3 to 130 yr old. We sampled each patch with a minimum of 20 funnel-type throughfall collectors over a continuous 2month period that had nearly 900 mm of rain. During the same period, we acquired forest inventory data and derived several forest structural attributes. We then applied simple and multiple regression models (Bayesian model averaging, BMA) and identified those vegetation parameters that had the strongest influence on the variation of canopy interception. Our analyses yielded three main findings. First, canopy interception changed rapidly during forest succession. After only a decade, throughfall volumes approached levels that are typical for mature forests. Second, a parsimonious (simple linear regression) model based on the ratio of the basal area of small stems to the total basal area outperformed more complex multivariate models (BMA approach). Third, based on complementary forest inventory data, we show that the influence of young secondary forests on interception in realworld fragmented landscapes might be detectable only in regions with a substantial fraction of young forests. Our re-sults suggest that where entire catchments undergo forest regrowth, initial stages of succession may be associated with a substantial decrease of streamflow generation. Our results further highlight the need to study hydrological processes in all forest succession stages, including early ones.
Nowadays, an increasing amount of seismic data is collected by daily observatory routines. The basic step for successfully analyzing those data is the correct detection of various event types. However, the visually scanning process is a time-consuming task. Applying standard techniques for detection like the STA/LTAtrigger still requires the manual control for classification. Here, we present a useful alternative. The incoming data stream is scanned automatically for events of interest. A stochastic classifier, called hidden Markov model, is learned for each class of interest enabling the recognition of highly variable waveforms. In contrast to other automatic techniques as neural networks or support vector machines the algorithm allows to start the classification from scratch as soon as interesting events are identified. Neither the tedious process of collecting training samples nor a time-consuming configuration of the classifier is required. An approach originally introduced for the volcanic task force action allows to learn classifier properties from a single waveform example and some hours of background recording. Besides a reduction of required workload this also enables to detect very rare events. Especially the latter feature provides a milestone point for the use of seismic devices in alpine warning systems. Furthermore, the system offers the opportunity to flag new signal classes that have not been defined before. We demonstrate the application of the classification system using a data set from the Swiss Seismological Survey achieving very high recognition rates. In detail we document all refinements of the classifier providing a step-by-step guide for the fast set up of a well-working classification system.
The terrestrial biosphere is a key component of the global carbon cycle and its carbon balance is strongly influenced by climate. Continuing environmental changes are thought to increase global terrestrial carbon uptake. But evidence is mounting that climate extremes such as droughts or storms can lead to a decrease in regional ecosystem carbon stocks and therefore have the potential to negate an expected increase in terrestrial carbon uptake. Here we explore the mechanisms and impacts of climate extremes on the terrestrial carbon cycle, and propose a pathway to improve our understanding of present and future impacts of climate extremes on the terrestrial carbon budget.
The geomorphic evolution of the Makran Range of SE-Iran and SW-Pakistan has been controlled by the prevailing SW-Asian monsoon and Mediterranean winter rainfall climate and the surface uplift processes resulting from the Arabia-Eurasia collision. The impact of climate on Quaternary fluvial and alluvial sequence formation and their regional correlation has been little investigated due to limited age control of these sequences. Using Be-10 cosmogenic nuclide exposure ages we established a Middle to Late Pleistocene terrace chronology. Our record tentatively indicates that terrace levels were abandoned towards the transition to or during warmer/pluvial periods (interglacials and/or interstadials) back to Marine Isotope Stage (MIS) 7, but abandoned ages show a large spread. It is hypothesized that pluvial phases correspond with times of enhanced SW-monsoons and a northward shift of the Intertropical Convergence Zone (ITCZ). Furthermore, orbital periodidties can be deduced on frequencies related to obliquity and precession cycles. Overall, caution has to be placed in sampling and interpreting alluvial deposits, which may have complex inheritance patterns and spatially and temporarily variable catchment erosion histories and terrace-channel dynamics.
Beside the dominant climate control on terrace formation, elevated channel steepness indices around major thrusts and numerous knickpoints indicate an additionally tectonic influence on terrace formation. Local incision rates (mean similar to 0.6-0.8 min.a(-1)) are variable in space and time but are similar to uplift rates obtained from coastal terraces and thus suggest a regional surface uplift. (C) 2013 Elsevier B.V. All rights reserved.
Retention and transformation of nutrients within a river catchment are important mechanisms influencing water quality measured at the watershed outlet. Nutrient storage and reduction can occur in soils as well as in the river and should be considered in water quality modelling. Consideration is possible using various methods at several points during modelling cascade. The study compares the effects of five different equation sets implemented into the Soil and Water Integrated Model (SWIM), one describing terrestrial and four in-stream retention with a rising complexity (including algal growth and death at the highest complexity level). The influences of the different methods alone and in combinations on water quality model outputs (NO3-N, NH4-N, PO4-P) were analyzed for the outlet of the large-scale Saale basin in Germany. Experiments revealed that nutrient forms coming primarily from diffuse sources are mostly influenced by retention processes in the soils of the catchment, and river processes are less important. Nutrients introduced to the river mainly by point sources are more subject to retention by in-stream processes, but both nutrient retention and transformation processes in soils and rivers have to be included. Although the best overall results could be achieved at the highest complexity level, the calibration efforts for this case are extremely high, and only minor improvements of overall model performance with the highest complexity were detected. Therefore, it could be reasoned that for some research questions also less complex model approaches would be sufficient, which could help to reduce unnecessary complexity and diminish high uncertainty in water quality modelling at the catchment scale. (C) 2013 Elsevier B.V. All rights reserved.
Finding evidence for ultrahigh-pressure (UHP) metamorphism in crustal rocks is far from straightforward. The index minerals coesite and diamond are incredibly inconspicuous and are therefore difficult to use as UHP prospecting tools. Consequently, petrographers rely on recognizing subtle breakdown microstructures that result from pressure release during the return to the surface of the once deeply buried rock. Similarly, many other UHP minerals are first suspected on the basis of typical reaction or exsolution microstructures. Thus, the painstaking use of microscopic techniques has been fundamental to the tremendous advances in characterizing, quantifying, and understanding macroscopic-scale, deep continental subduction, rapid exhumation, and mountain-building processes.
The deep thermal field in sedimentary basins can be affected by convection, conduction or both resulting from the structural inventory, physical properties of geological layers and physical processes taking place therein. For geothermal energy extraction, the controlling factors of the deep thermal field need to be understood to delineate favorable drill sites and exploitation compartments. We use geologically based 3-D finite element simulations to figure out the geologic controls on the thermal field of the geothermal research site Gro Schonebeck located in the E part of the North German Basin. Its target reservoir consists of Permian Rotliegend clastics that compose the lower part of a succession of Late Carboniferous to Cenozoic sediments, subdivided into several aquifers and aquicludes. The sedimentary succession includes a layer of mobilized Upper Permian Zechstein salt which plays a special role for the thermal field due to its high thermal conductivity. Furthermore, the salt is impermeable and due to its rheology decouples the fault systems in the suprasalt units from subsalt layers. Conductive and coupled fluid and heat transport simulations are carried out to assess the relative impact of different heat transfer mechanisms on the temperature distribution. The measured temperatures in 7 wells are used for model validation and show a better fit with models considering fluid and heat transport than with a purely conductive model. Our results suggest that advective and convective heat transport are important heat transfer processes in the suprasalt sediments. In contrast, thermal conduction mainly controls the subsalt layers. With a third simulation, we investigate the influence of a major permeable and of three impermeable faults dissecting the subsalt target reservoir and compare the results to the coupled model where no faults are integrated. The permeable fault may have a local, strong impact on the thermal, pressure and velocity fields whereas the impermeable faults only cause deviations of the pressure field.
The last known eruption at Cerro Machin Volcano (CMV) in the Central Cordillera of Colombia occurred 900 years BP and ended with the formation of a dacitic lava dome. The dome rocks contain both normally and reversely zoned plagioclase (An(24-54)), unzoned and reversely zoned amphiboles of dominantly tschermakite and pargasite/magnesio-hastingsite composition and olivine xenocrysts (Fo = 85-88) with amphibole/clinopyroxene overgrowth, all suggesting interaction with mafic magma at depth. Plagioclase additionally exhibits complex oscillatory zoning patterns reflecting repeated replenishment, fractionation and changes in intrinsic conditions in the magma reservoir. Unzoned amphiboles and cores of the reversely zoned amphiboles give identical crystallization conditions of 910 +/- 30 degrees C and 360 +/- 70 MPa, corresponding to a depth of about 13 +/- 2 km, at moderately oxidized conditions (f(O2) = +0.5 +/- 0.2 Delta NNO). The water content in the melt, calculated based on amphibole chemistry, is 7.1 +/- 0.4 wt.%. Rims of the reversely zoned amphiboles are relatively enriched in MgO and yield higher crystallization temperatures (T = 970 +/- 25 degrees C), slightly lower melt H2O contents (6.1 +/- 0.7 wt.%) and overlapping pressures (410 +/- 100 MPa). We suggest that these rims crystallized following an influx of mafic melt into a resident magma reservoir at mid-crustal depths, further supported by the occurrence of xenocrystic olivine. Crystallization of biotite, albite-rich plagioclase and quartz occurred at comparatively low temperatures (probably <800 degrees C) during early stages of ascent or storage at shallower levels. Based on amphibole mineral chemistry, the felsic resident melt had a rhyolitic composition (71 +/- 2 wt.% SiO2), whereas the hybrid magma, from which the amphibole rims crystallized, was dacitic (64 +/- 3 wt.% SiO2). The bulk rock chemistry of the CMV lava dome dacites is homogenous. They have elevated (La/Nb)(N) ratios of 3.8-4.5, typical for convergent margin magmas, and display several geochemical characteristics, of adakites. Both Sr and Nd isotope compositions (Sr-87/Sr-86 similar to 0.70497, Nd-143/Nd-144 similar to 0.51267) are among the most radiogenic observed for the Northern Volcanic Zone of the Andes. They are distinct from oceanic crust that has been subducted in the region, pointing to a continental crustal control on the isotope composition and hence the adakitic signature, possibly in a crustal "hot zone".
Sophisticated methods have been developed and become standard in analysing floods as well as for assessing flood risk. However, increasingly critique of the current standards and scientific practice can be found both in the flood hydrology community as well as in the risk community who argue that the considerable amount of information already available on natural disasters has not been adequately deployed and brought to effective use. We describe this phenomenon as a failure to synthesize knowledge that results from barriers and ignorance in awareness, use and management of the entire spectrum of relevant content, that is, data, information and knowledge. In this paper we argue that the scientific community in flood risk research ignores event-specific analysis and documentations as another source of data. We present results from a systematic search that includes an intensive study on sources and ways of information dissemination of flood-relevant publications. We obtain 186 documents that contain information on the sources, pathways, receptors and/or consequences for any of the 40 strongest trans-basin floods in Germany in the period 1952-2002. This study therefore provides the most comprehensive metadata collection of flood documentations for the considered geographical space and period. A total of 87.5% of all events have been documented, and especially the most severe floods have received extensive coverage. Only 30% of the material has been produced in the scientific/academic environment, and the majority of all documents (about 80%) can be considered grey literature (i.e. literature not controlled by commercial publishers). Therefore, ignoring grey sources in flood research also means ignoring the largest part of knowledge available on single flood events (in Germany). Further, the results of this study underpin the rapid changes in information dissemination of flood event literature over the last decade. We discuss the options and obstacles of incorporating this data into the knowledge-building process in light of the current technological developments and international, interdisciplinary debates for data curation.
The northeastern margin of the Tibetan Plateau is a tectonically active region consisting of a series of faults with bounded intermountain basins and is located in the transition zone between the Tibetan Plateau and the Loess Plateau. Active deformation that may affect the topography in this region can be quantified using geomorphic indices. Therefore, we applied geomorphic indices such as the hypsometric integral and the stream length gradient index to infer neo-tectonics in the northeastern margin of the Tibetan Plateau. Different time-scaled geodetic leveling data and river incision rates were also integrated into the investigation. The results show that the hypsometric integrals are not significantly affected by lithology but spatially correspond to the hanging walls of thrust faults. The hypsometric integrals are also positively correlated with the leveling data. Although the stream length gradient index is influenced by lithology, its most pronounced anomalies of the stream length gradient are associated with the thrust faults. Consequently, the uplift in the northeast margin of the Tibetan Plateau appeared to be concentrated along the hanging walls of the thrust faults.
Facies bodies in geostatistical models of deep-water depositional environments generally represent channel-levee-overbank-lobe morphologies. Such models adequately capture one set of the erosional and depositional processes resulting from turbidity currents traveling downslope to the ocean basin floor. However, depositional morphologies diverge from the straight forward channel-levee-overbank-lobe paradigm when the topography of the slope or the shape of the basin impacts the timing and magnitude of turbidity current deposition. Subaqueous mass-transport-deposits (MTDs) present the need for an exception to the channel-levee-overbank-lobe archetype. Irregular surface topography of subaqueous MTDs can play a primary role in controlling sand deposition from turbidity currents. MTD topography creates mini-basins in which sand accumulates in irregularly-shaped deposits. These accumulations are difficult to laterally correlate using well-log data due to their variable and unpredictable shape and size. Prediction is further complicated because sandstone bodies typical of this setting are difficult to resolve in seismic-reflection data. An event-based model is presented, called DFTopoSim, which simulates debris flows and turbidity currents. The accommodation space on top of and between debris flow lobes is filled in by sand from turbidity currents. When applied to a subsurface case in the Molasse Basin of Upper Austria, DFTopoSim predicts sand packages consistent with observations from core, well, and seismic data and the interpretation of the sedimentologic processes. DFTopoSim expands the set of available geostatistical deep-water depositional models beyond the standard channel-levee-overbank-lobe model.
Emerged marine terraces and paleoshorelines along plate margins are prominent geomorphic markers that can be used to quantify the rates and patterns of crustal deformation. The northern margin of the Central Anatolian Plateau has been interpreted as an actively deforming orogenic wedge between the North Anatolian Fault and the Black Sea. Here we use uplifted marine terraces across principal faults on the Sinop Peninsula at the central northern side of the Pontide orogenic wedge to unravel patterns of Quaternary faulting and orogenic wedge behavior. We leveled the present-day elevations of paleoshorelines and dated marine terrace deposits using optically stimulated luminescence (OSL) to determine coastal uplift. The elevations of the paleoshorelines vary between 4 +/- 0.2 and 67 +/- 1.4 m above sea level and OSL ages suggest terrace formation episodes during interglacial periods at ca 125, 190, 400 and 570 ka, corresponding to marine isotopic stages (MIS) 5e, 7a, 11 and 15. Mean apparent vertical displacement rates (without eustatic correction) deduced from these terraces range between 0.02 and 0.18 mm/a, with intermittent faster rates of up to 0.26 mm/a. We obtained higher rates at the eastern and southern parts of the peninsula, toward the hinterland, indicating non-uniform uplift across the different morphotectonic segments of the peninsula. Our data are consistent with active on- and offshore faulting across the Sinop Peninsula. When integrated with regional tectonic observations, the faulting pattern reflects shortening distributed over a broad region of the northern margin of the Central Anatolian Plateau during the Quaternary.
The tectonically driven growth of mountains reflects the characteristics of the underlying fault systems and the applied tectonic forces. Over time, fault networks might be relatively static, but stress conditions could change and result in variations in fault slip orientation. Such a tectonic landscape would transition from a simple to a composite state: the topography of simple landscapes is correlated with a single set of tectonic boundary conditions, while composite landscapes contain inherited topography due to earlier deformation under different boundary conditions. We use fault interaction modeling to compare vertical displacement fields with topographic metrics to differentiate the two types of landscapes. By successively rotating the axis of maximum horizontal stress, we produce a suite of vertical displacement fields for comparison with real landscapes. We apply this model to a transpressional duplex in the south central Alborz Mountains of Iran, where NW oriented compression was superseded by neotectonic NE compression. The consistency between the modeled displacement field and real landforms indicates that the duplex topography is mostly compatible with the modern boundary conditions, but might include a small remnant from the earlier deformation phase. Our approach is applicable for various tectonic settings and represents an approach to identify the changing boundary conditions that produce composite landscapes. It may be particularly useful for identifying changes that occurred in regions where river profiles may no longer record a signal of the change or where the spatial pattern of uplift is complex.
Increases in animal products consumption and the associated environmental consequences have been a matter of scientific debate for decades. Consequences of such increases include rises in greenhouse gas emissions, growth of consumptive water use, and perturbation of global nutrients cycles. These consequences vary spatially depending on livestock types, their densities and their production system. In this letter, we investigate the spatial distribution of embodied crop calories in animal products. On a global scale, about 40% of the global crop calories are used as livestock feed (we refer to this ratio as crop balance for livestock) and about 4 kcal of crop products are used to generate 1 kcal of animal products (embodied crop calories of around 4). However, these values vary greatly around the world. In some regions, more than 100% of the crops produced is required to feed livestock requiring national or international trade to meet the deficit in livestock feed. Embodied crop calories vary between less than 1 for 20% of the livestock raising areas worldwide and greater than 10 for another 20% of the regions. Low values of embodied crop calories are related to production systems for ruminants based on fodder and forage, while large values are usually associated with production systems for non-ruminants fed on crop products. Additionally, we project the future feed demand considering three scenarios: (a) population growth, (b) population growth and changes in human dietary patterns and (c) changes in population, dietary patterns and feed conversion efficiency. When considering dietary changes, we project the global feed demand to be almost doubled (1.8-2.3 times) by 2050 compared to 2000, which would force us to produce almost equal or even more crops to raise our livestock than to directly nourish ourselves in the future. Feed demand is expected to increase over proportionally in Africa, South-Eastern Asia and Southern Asia, putting additional stress on these regions.
Changing food consumption patterns and associated greenhouse gas (GHG) emissions have been a matter of scientific debate for decades. The agricultural sector is one of the major GHG emitters and thus holds a large potential for climate change mitigation through optimal management and dietary changes. We assess this potential, project emissions, and investigate dietary patterns and their changes globally on a per country basis between 1961 and 2007. Sixteen representative and spatially differentiated patterns with a per capita calorie intake ranging from 1,870 to >3,400 kcal/day were derived. Detailed analyses show that low calorie diets are decreasing worldwide, while in parallel diet composition is changing as well: a discernable shift towards more balanced diets in developing countries can be observed and steps towards more meat rich diets as a typical characteristics in developed countries. Low calorie diets which are mainly observable in developing countries show a similar emission burden than moderate and high calorie diets. This can be explained by a less efficient calorie production per unit of GHG emissions in developing countries. Very high calorie diets are common in the developed world and exhibit high total per capita emissions of 3.7-6.1 kg CO2eq./day due to high carbon intensity and high intake of animal products. In case of an unbridled demographic growth and changing dietary patterns the projected emissions from agriculture will approach 20 Gt CO2eq./yr by 2050.
A high resolution multi proxy (pollen, grain size, total organic carbon) record from a small mountain lake (Lake Khuisiin; 46.6 degrees N, 101.8 degrees E; 2270 m a.s.l.) in the south eastern Khangai Mountains of central Mongolia has been used to explore changes in vegetation and climate over the last 1200 years. The pollen data indicates that the vegetation changed from dry steppe dominated by Poaceae and Artemisia (ca AD 760-950), to Larix forest steppe (ca AD 950-1170), Larix Betula forest steppe (ca AD 1170-1380), meadow dominated by Cyperaceae and Poaceae (ca AD 1380-1830), and Larix Betula forest steppe (after similar to AD 1830). The cold-wet period between AD 1380 and 1830 may relate to the Little Ice Age. Environmental changes were generally subtle and climate change seems to have been the major driver of variations in vegetation until at least the early part of the 20th century, suggesting that either the level of human activity was generally low, or the relationship between human activity and vegetation did not alter substantially between AD 760 and 1830. A review of centennial scale moisture records from China and Mongolia revealed that most areas experienced major changes at ca AD 1500 and AD 1900. However, the moisture availability since AD 1500 varied between sites, with no clear regional pattern or relationship to present day conditions. Both the reconstructions and the moisture levels simulation on a millennium scale performed in the MPI Earth System Model indicate that the monsoon-westerlies transition area shows a greater climate variability than those areas influenced by the westerlies, or by the summer monsoon only.
Purpose: Dry land vegetation is expected to respond sensitively to climate change and the projected variability of rainfall events. Rainfall as a water source is an obvious factor for the water supply of vegetation. However, the interaction of water and surface on rocky desert slopes with a patchy soil cover is also vital for vegetation in drylands. In particular, runoff on rocky surfaces and infiltration capacity of soil patches determine plant available water. Process-based studies into rock-soil interaction benefit from rainfall simulation, but require an approach accounting for the micro-scale heterogeneity of the slope surfaces. This study therefore aims at developing a suitable procedure for examining rock-soil interaction and the relevance of soil volume for storing plant available water in the northern Negev, Israel.
Materials and methods: To determine the amount of rainfall required to fill the available soil water storage capacity rainfall simulation experiments were conducted. The design of the rainfall-simulator and the selection of the plots aimed specifically at observing infiltration into small soil patches on a micro-scale relevant for the prevalent vegetation cover.
Results and discussion: The preliminary results of the study in the Negev Desert indicate that the ratio between soil volume and frequency of rainfall events determine the effect of climate change on plant available water and thus ultimately vegetation cover.
Conclusions: Based on the experiments examining runoff and soil moisture the qualitative understanding of hillslope ecohydrology in a rocky desert environment can be expanded into a quantitative assessment of the potential impact of varying rainfall conditions. The study also illustrates the contribution of rainfall simulation experiments for studies on the impact of climate change.
Explaning change in flood hazard in the Mekong river : the hypothesis of nonstationary variance
(2013)
Digital flow networks derived from digital elevation models (DEMs) sensitively react to errors due to measurement, data processing and data representation. Since high-resolution DEMs are increasingly used in geomorphological and hydrological research, automated and semi-automated procedures to reduce the impact of such errors on flow networks are required. One such technique is stream-carving, a hydrological conditioning technique to ensure drainage connectivity in DEMs towards the DEM edges. Here we test and modify a state-of-the-art carving algorithm for flow network derivation in a low-relief, agricultural landscape characterized by a large number of spurious, topographic depressions. Our results show that the investigated algorithm reconstructs a benchmark network insufficiently in terms of carving energy, distance and a topological network measure. The modification to the algorithm that performed best, combines the least-cost auxiliary topography (LCAT) carving with a constrained breaching algorithm that explicitly takes automatically identified channel locations into account. We applied our methods to a low relief landscape, but the results can be transferred to flow network derivation of DEMs in moderate to mountainous relief in situations where the valley bottom is broad and flat and precise derivations of the flow networks are needed.
Through their relevance for sediment budgets and the sensitivity of geomorphic systems, geomorphic coupling and (sediment) connectivity represent important topics in geomorphology. Since the introduction of the systems perspective to physical geography by Chorley and Kennedy (1971), a catchment has been perceived as consisting of landscape elements (e.g. landforms, subcatchments) that are coupled by geomorphic processes through sediment transport. In this study, we present a novel application of mathematical graph theory to explore the network structure of coarse sediment pathways in a central alpine catchment. Numerical simulation models for rockfall, debris flows, and (hillslope and channel) fluvial processes are used to establish a spatially explicit graph model of sediment sources, pathways and sinks. The raster cells of a digital elevation model form the nodes of this graph, and simulated sediment trajectories represent the corresponding edges. Model results are validated by visual comparison with the field situation and aerial photos. The interaction of sediment pathways, i.e. where the deposits of a geomorphic process form the sources of another process, forms sediment cascades, represented by paths (a succession of edges) in the graph model. We show how this graph can be used to explore upslope (contributing area) and downslope (source to sink) functional connectivity by analysing its nodes, edges and paths. The analysis of the spatial distribution, composition and frequency of sediment cascades yields information on the relative importance of geomorphic processes and their interaction (however regardless of their transport capacity). In the study area, the analysis stresses the importance of mass movements and their interaction, e.g. the linkage of large rockfall source areas to debris flows that potentially enter the channel network. Moreover, it is shown that only a small percentage of the study area is coupled to the channel network which itself is longitudinally disconnected by natural and anthropogenic barriers. Besides the case study, we discuss the methodological framework and alternatives for node and edge representations of graph models in geomorphology. We conclude that graph theory provides an excellent methodological framework for the analysis of geomorphic systems, especially for the exploration of quantitative approaches towards sediment connectivity.
Soilscapes of the post-glacial morainic regions of the youngest glaciation are characterized by small hydrological kettle hole catchments forming hummocky soil landscapes. The spatial heterogeneity of subsurface structures as well as erosion-controlled pedogenesis under arable land use may complicate hydrological modeling. Our aim was to generate a soil landscape model for a small representative kettle hole catchment based on geoelectrical exploration and soil profile information. For a 1-ha catchment located in the northeastern German lowlands near the town of Prenzlau, electrical resistivity transects were determined by a multi electrode system (IMPETUS 12 Fs) and electrical conductivity (ECa) was mapped by using the electromagnetic induction (EMI) device EM38DD in both the vertical and horizontal modes. The 1-m digital elevation model (DEM) was obtained by kriging from high resolution manual elevation data determined with a leveling device (ZEISS Ni 40). Soil profile data from 26 boreholes distributed radially around the central pond were used to identify boundaries between soil horizons. The soil is characterized by varying topography and morphology of diagnostic horizons such as M- (colluvium), Bt- (clay illuviation), and C- (parent glacial till). By EMI mapping we identified (i) the boundary between erosive and colluvial areas around the kettle hole, and modeled (ii) the subsurface morphology of loamy horizons. Electrical resistivity tomography results coincide with these findings and allow for distinguishing between sandy and loamy dominated areas both in vertical and horizontal direction, respectively. This soil model of soil textural properties could be used for hydrological modeling.
The knowledge of the local soil structure is important for the assessment of seismic hazards. A widespread, but time-consuming technique to retrieve the parameters of the local underground is the drilling of boreholes. Another way to obtain the shear wave velocity profile at a given location is the inversion of surface wave dispersion curves. To ensure a good resolution for both superficial and deeper layers, the used dispersion curves need to cover a wide frequency range. This wide frequency range can be obtained using several arrays of seismic sensors or a single array comprising a large number of sensors. Consequently, these measurements are time-consuming. A simpler alternative is provided by the use of the ellipticity of Rayleigh waves. The frequency dependence of the ellipticity is tightly linked to the shear wave velocity profile. Furthermore, it can be measured using a single seismic sensor. As soil structures obtained by scaling of a given model exhibit the same ellipticity curve, any inversion of the ellipticity curve alone will be ambiguous. Therefore, additional measurements which fix the absolute value of the shear wave velocity profile at some points have to be included in the inversion process. Small-scale spatial autocorrelation measurements or MASW measurements can provide the needed data. Using a theoretical soil structure, we show which parts of the ellipticity curve have to be included in the inversion process to get a reliable result and which parts can be omitted. Furthermore, the use of autocorrelation or high-frequency dispersion curves will be highlighted. The resulting guidelines for inversions including ellipticity data are then applied to real data measurements collected at 14 different sites during the European NERIES project. It is found that the results are in good agreement with dispersion curve measurements. Furthermore, the method can help in identifying the mode of Rayleigh waves in dispersion curve measurements.
In this study, we evaluated the potential of the hydrogen isotopic composition of algal lipid biomarkers as a proxy for past hydroclimatic variability in hypersaline Isabel Lake, Mexico (Eastern Pacific). We compared rainfall variability recorded in the region over the last 65 years with changes in delta D values of the most abundant compounds preserved in the uppermost 16 cm of lake sediment. Changes in delta D values of the 1,15-C-32 diol (delta D-diol), a specific biomarker of algal populations, were related to rainfall variability; specifically, n-alkyl diols were more deuterium-enriched (depleted) during wetter (drier) periods. Strikingly, neither the magnitude of lipid biomarker isotopic changes over interannual timescales (of up to 70-80 parts per thousand) nor the direction of that variability can be explained by changes in delta D values of the water source or salinity fluctuations (approximately 30 on the practical salinity scale) controlled by seasonal rainfall. However, changes in sedimentary biomarker composition, higher total organic carbon content and less negative delta C-13 values of the 1,15-C-32 diol indicate enhanced algal growth during wetter periods. We find that these conditions result in less negative delta D values of n-alkyl diols. We hypothesize that due to higher lipid demand during enhanced algal growth, an increasing proportion of hydrogen for lipid synthesis is derived from the cytosol via oxidation of polysaccharides, which may cause a deuterium enrichment of the acetogenic compounds. This study has significant implications for paleohydrological reconstructions using algal lipid delta D values, particularly in highly seasonal environments such as Isabel Lake. In such environments, delta D values of specific algal lipid biomarkers may not record the full seasonal cycle in source water delta D but appear to be mainly controlled by the physiological state of algal populations. Our data provide the first evidence that changes in D/H fractionation due to algal growth conditions can be recorded in sediments. For paleoclimate reconstructions in such environments, algal growth conditions should be constrained with additional proxy data (delta C-13 values of the same biomarkers), as the net D/H fractionation between water and lipids may not have been constant over time.
North of Naran in the Kaghan Valley (NE Pakistan), the metabasites of the melange units lying below the Kohistan Arc, contain glaucophane. Typically they reflect blueschist-metamorphic conditions (0.7 GPa, 400 degrees C). Associated graphite-rich metapelites with quartz veins underwent upper greenschist to amphibolite conditions. Near Naran we observed in quartz grains of type 3 veins first minute relics of Fe-Mg carpholite indicating earlier blueschist metamorphic conditions. P-T estimates indicate 1.2-1.6 GPa at 380-410 degrees C, pressure and temperature values typical for blueschist metamorphic conditions. Changes in mineral assemblages and abundant sudoite component in associated chlorite point to a pressure drop after peak I conditions. We assign the observed changes to peak I conditions occurring during a Cretaceous subduction event. Temperatures estimated with Raman graphite-thermometry clearly indicate a significant subsequent rise of post-peak I temperatures up to 500 degrees C. This is compatible with the amphibolite peak II assigned to the Tertiary continental collision that leads to subduction of the Indian Plate and ultra-high-pressure metamorphism. During subduction the blueschist metamorphic metapelites underwent dehydration, which caused alteration in the overlying lithospheric mantle. In a hydrated lithospheric mantle density is significantly reduced which enhanced subduction of continental crust in the Higher Himalaya. This P-T evolution is typical for a collision orogen with a high plateau but remarkably contrasting findings from Eastern Anatolia, where plateau building is in "statu nascendi" (e.g., Oberhänsli et al., 2010).
Extremely rare veinlets and reaction textures composed of symplectites of olivine (similar to Fo(43-55)) + plagioclase +/- spinel +/- ilmenite, associated with more common pyroxene + plagioclase and amphibole + plagioclase varieties, are preserved within eclogites and garnet pyroxenites in the Moldanubian Zone of the Bohemian Massif. Thermodynamic modelling integrated with conventional geothermometry conducted on an eclogite reveals that the symplectite-forming stage occurred at high T (similar to 850 degrees C) and low P (< 6 and > 2 center dot 5 kbar). The development of the different symplectite types reflects reactions that took place in micro-scale domains. The breakdown of high-P garnet controlled the formation of olivine-bearing and amphibole + plagioclase symplectites, whereas breakdown of high-P omphacite led to formation of pyroxene + plagioclase symplectites. In addition, post-eclogite facies but pre-symplectite stage porphyroblastic amphibole and phlogopite were also replaced by olivine-bearing symplectites. Material transfer calculations and thermodynamic modelling indicate that the formation of different symplectite types was linked despite their different bulk compositions. For example, the olivine-bearing symplectites gained Fe +/- Mg, whereas adjacent amphibole + plagioclase and pyroxene + plagioclase symplectites show losses in Fe and Mg; Al, Si and Ca were also variably exchanged. The olivine-bearing symplectites were particularly sensitive to Na despite the small concentration of this element. In eclogites where Na was readily available, the plagioclase composition in the olivine-bearing symplectites shifted from pure anorthite to bytownite, with the less calcic feldspar partitioning Si and inhibiting the formation of orthopyroxene. This regional high-T, low-P granulite-facies symplectite overprint may have been caused by advective heat loss from rapidly exhumed high-T, high-P granulitic bodies (Gfohl Unit) that were emplaced into and over the middle crust (Monotonous and Varied Series) during Carboniferous continent-continent collision.
In the recent past, the Alpine Lech valley (Austria) experienced three damaging flood events within 6 years despite the various structural flood protection measures in place. For an improved flood risk management, the analysis of flood damage potentials is a crucial component. Since the expansion of built-up areas and their associated values is seen as one of the main drivers of rising flood losses, the goal of this study is to analyze the spatial development of the assets at risk, particularly of residential areas, due to land use changes over a historic period (since 1971) and up to possible shifts in future (until 2030). The analysis revealed that the alpine study area was faced to remarkable land use changes like urbanization and the decline of agriculturally used grassland areas. Although the major agglomeration of residential areas inside the flood plains took place before 1971, a steady growth of values at risk can still be observed until now. Even for the future, the trend is ongoing, but depends very much on the assumed land use scenario and the underlying land use policy. Between 1971 and 2006, the annual growth rate of the damage potential of residential areas amounted to 1.1 % ('constant values,' i.e., asset values at constant prices of reference year 2006) or 3.0 % ('adjusted values,' i.e., asset values adjusted by GDP increase at constant prices of reference year 2006) for three flood scenarios. For the projected time span between 2006 and 2030, a further annual increase by 1.0 % ('constant values') or even 4.2 % ('adjusted values') may be possible when the most extreme urbanization scenario 'Overall Growth' is considered. Although socio-economic development is regarded as the main driver for increasing flood losses, our analysis shows that settlement development does not preferably take place within flood prone areas.
Sediments of a thermokarst system on the north-eastern Tibetan Plateau were studied to infer changes in the lacustrine depositional environment related to climatic changes since the early Holocene. The thermokarst pond with a length of 360 m is situated in a 14.5 x 6 km tectonically unaffected intermontane basin, which is underlain by discontinuous permafrost.
A lake sediment core and bankside lacustrine onshore deposits were analysed. Additionally, fossil lake sediments were investigated, which document a former lake-level high stand. The sediments are mainly composed of marls with variable amounts of silt carbonate micrite, and organic matter.
On the basis of sedimentological (grain size data), geochemical (XRF), mineralogical (XRD) and micropaleontological data (ostracods and chironomide assemblages) a reconstruction of a paleolake environment was achieved.
Lacustrine sediments with endogenic carbonate precipitation suggest a lacustrine environment since at least 19.0 cal ka BP. However, because of relocation and reworking processes in the lake, the sediments did not provide distinct information about the ultimate formation of the lake. The high amount of endogenic carbonate suggests prolonged still-water conditions at about 9.3 cal ka BP. Ostracod shells and chironomid head capsules in fossil lake sediments indicate at least one former lake-level high stand, which were developed between the early and middle Holocene. From the late Holocene the area was possibly characterized by a lake-level decline, documented by a hiatus between lacustrine sediments and a reworked loess or loess-like horizon. After the lake-level decline and the following warming period, the area was affected by thermally-induced subsidence and a re-flooding of the basin because of thawing permafrost.
Improving our understanding of biodiversity and ecosystem functioning and our capacity to inform ecosystem management requires an integrated framework for functional biodiversity research (FBR). However, adequate integration among empirical approaches (monitoring and experimental) and modelling has rarely been achieved in FBR. We offer an appraisal of the issues involved and chart a course towards enhanced integration. A major element of this path is the joint orientation towards the continuous refinement of a theoretical framework for FBR that links theory testing and generalization with applied research oriented towards the conservation of biodiversity and ecosystem functioning. We further emphasize existing decision-making frameworks as suitable instruments to practically merge these different aims of FBR and bring them into application. This integrated framework requires joint research planning, and should improve communication and stimulate collaboration between modellers and empiricists, thereby overcoming existing reservations and prejudices. The implementation of this integrative research agenda for FBR requires an adaptation in most national and international funding schemes in order to accommodate such joint teams and their more complex structures and data needs.
While sea level rise is one of the most likely consequences of climate change, the provoked costs remain highly uncertain. Based on a block-maxima approach, we provide a stochastic framework to estimate the increase of expected damages with sea level rise as well as with meteorological changes and demonstrate the application to two case studies. In addition, the uncertainty of the damage estimations due to the stochastic nature of extreme events is studied. Starting with the probability distribution of extreme flood levels, we calculate the distribution of implied damages in a specific region employing stage-damage functions. Universal relations of the expected damages and their standard deviation, which demonstrate the importance of the shape of the damage function, are provided. We also calculate how flood protection reduces the damages leading to a more complex picture, where the extreme value behavior plays a fundamental role. Citation: Boettle, M., D. Rybski, and J. P. Kropp (2013), How changing sea level extremes and protection measures alter coastal flood damages, Water Resour. Res., 49, 1199-1210, doi: 10.1002/wrcr.20108.
During the African Humid Period (AHP, 15-5 ka BP) an almost 300 m deep paleo-lake covering 2200 km(2) developed in the Suguta Valley, in the Northern Kenya Rift Data from lacustrine sediments and paleo-shorelines indicate that a large paleo-lake already existed by 13.9 ka BP, and record rapid water level fluctuations of up to 100 m within periods of 100 years or less, and a final lowstand at the end of the AHP (5 ka BP). We used a hydro-balance model to assess the abruptness of these water level fluctuations and identify their causes. We observed that fluctuations within the AHP were caused by abrupt changes in precipitation of 26-40%. Despite the absence of continuous lacustrine data documenting the onset of the AHP in the Suguta Valley, we conclude from the hydro-balance model that only an abrupt onset to the AHP, prior to 14.8 ka BP, could have led to high water levels recorded. The modeling results suggest that the sudden increase in rainfall was the direct consequence of an eastward migration of the Congo Air Boundary (CAB), caused by an enhanced atmospheric pressure gradient between East Africa and southern Asia during a northern hemisphere (NH) summer insolation maximum. In contrast the end of the AHP must have been gradual despite an abrupt change in the source of precipitation when a decreasing pressure gradient between Asia and Africa prevented the CAB from reaching the study area. This abruptness was probably buffered by a contemporaneous change in precession producing an insolation maximum at the equator during September-October. This change would have meant that the only rain source was the Intertropical Convergence Zone (IT CZ), which would have carried a greater amount of moisture during the short rainy season thus slowing the fall in water level over a period of about 1000 years in association with the reduction in insolation. The results of this study provide an indication of the amount of time available for humans in north-eastern Africa to adapt in response to a changing climate, from hunting and gathering to farming and herding.
Reliable estimations of magnitude of completeness (M-c) are essential for a correct interpretation of seismic catalogues. The spatial distribution of M-c may be strongly variable and difficult to assess in mining environments, owing to the presence of galleries, cavities, fractured regions, porous media and different mineralogical bodies, as well as in consequence of inhomogeneous spatial distribution of the seismicity. We apply a 3-D modification of the probabilistic magnitude of completeness (PMC) method, which relies on the analysis of network detection capabilities. In our approach, the probability to detect an event depends on its magnitude, source receiver Euclidian distance and source receiver direction. The suggested method is proposed for study of the spatial distribution of the magnitude of completeness in a mining environment and here is applied to a 2-months acoustic emission (AE) data set recorded at the Morsleben salt mine, Germany. The dense seismic network and the large data set, which includes more than one million events, enable a detailed testing of the method. This method is proposed specifically for strongly heterogeneous media. Besides, it can also be used for specific network installations, with sensors with a sensitivity, dependent on the direction of the incoming wave (e.g. some piezoelectric sensors). In absence of strong heterogeneities, the standards PMC approach should be used. We show that the PMC estimations in mines strongly depend on the source receiver direction, and cannot be correctly accounted using a standard PMC approach. However, results can be improved, when adopting the proposed 3-D modification of the PMC method. Our analysis of one central horizontal and vertical section yields a magnitude of completeness of about M-c approximate to 1 (AE magnitude) at the centre of the network, which increases up to M-c approximate to 4 at further distances outside the network; the best detection performance is estimated for a NNE-SSE elongated region, which corresponds to the strike direction of the low-attenuating salt body. Our approach provides us with small-scale details about the capability of sensors to detect an earthquake, which can be linked to the presence of heterogeneities in specific directions. Reduced detection performance in presence of strong structural heterogeneities (cavities) is confirmed by synthetic waveform modelling in heterogeneous media.
The coastal stretch of north-eastern Mediterranean Morocco holds vitally important ecological, social, and economic functions. The implementation of large-scale luxury tourism resorts shall push socio-economic development and facilitate the shift from a mainly agrarian to a service economy. Sufficient water availability and intact beaches are among the key requirements for the successful realization of regional development plans. The water situation is already critical, additional water-intense sectors could overstrain the capacity of water resources. Further, coastal erosion caused by sea-level rise is projected. Regional climate change is observable, and must be included in regional water management. Long-term climate trends are assessed for the larger region (Moulouya basin) and for the near-coastal zone at Saidia. The amount of additional water demand is assessed for the large-dimensioned Saidia resort; including the monthly, seasonal and annual tourist per capita water need under inclusion of irrigated golf courses and garden areas. A shift of climate patterns is observed, a lengthening of the dry summer season, and as well a significant decline of annual precipitation. Thus, current water scarcity is mainly human-induced; however, climate change will aggravate the situation. As a consequence, severe environmental damage due to water scarcity is likely and could impinge on the quality of local tourism. The re-adjustment of current management routines is therefore essential. Possible adjustments are discussed and the analysis concludes with management recommendations for innovative regional water management of tourism facilities.
We integrate the information of multiple tomographic models acquired from the earth's surface by modifying a statistical approach recently developed for the integration of cross-borehole tomographic models. In doing so, we introduce spectral cluster analysis as the new core of the model integration procedure to capture the spatial heterogeneity present in all considered tomographic models and describe this heterogeneity in a fuzzy sense. Because spectral cluster algorithms analyze model structure locally, they are considered relatively robust with regard to systematically and spatially varying imaging capabilities typical for geophysical tomographic surveys conducted on the earth's surface. Using a synthetic aquifer example, a fuzzy spectral cluster algorithm can be used to integrate the information provided by 2D tomographic refraction seismic and DC resistivity surveys. The integrated information in the fuzzy membership domain is then used to derive an integrated zonal geophysical model outlining the major structural units present in both input models. We also explain how the fuzzy membership information can be used to identify optimal locations for sparse logging of additional target parameters, i.e., porosity information in our synthetic example. We demonstrate how this sparse porosity information can be extrapolated based on all tomographic input models. The resultant 2D porosity model matches the original porosity distribution reasonably well within the spatial resolution limits of the underlying tomographic models. Consecutively, we apply this approach to a field data base acquired over a former river channel. Sparse information about natural gamma radiation is available and extrapolated on the basis of the fuzzy membership information obtained by spectral cluster analysis of 2D P-wave velocity and electrical resistivity models. This field data shows that the presented parameter extrapolation procedure is robust, even if the locations of target parameter acquisition have not been optimized with regard to the fuzzy membership information.
We have undertaken a high resolution palaeoclimate reconstruction on radiocarbon dated palaeolake sediments from the Spiti valley, NW Himalaya. This site lies in the climatically sensitive winter westerlies and Indian Summer Monsoon (ISM) transitional regime and provides an opportunity to reconstruct the precipitation seasonality, and extreme precipitation events that are characterised by intensified erosion. The lake sediments reveal distinct lithofacies that provide evidence of changes in depositional environment and climate during early to mid Holocene (8.7-6.1 cal ka BP). We have identified three stages during the period of lake's existence: the Stage I (8.7-7.6 cal ka BP) is marked by lake establishment; Stage II (similar to 7.6-6.8 cal ka BP) by sustained cooler periods and weakened summer monsoon, and Stage III (similar to 6.8-6.1 cal ka BP) by a shift from colder to warmer climate with stronger ISM. We have identified several short term cooler periods at ca. 8.7, 8.5, 8.3 and 7.2-6.9 cal ka BP. Based on an overview of regional climate records we show that there is an abrupt switch in precipitation seasonality ca. 6.8 cal ka BP that is followed by the onset of the intensified monsoon in the NW Himalaya. (C) 2013 Elsevier Ltd and INQUA. All rights reserved.
The spatial distribution of soil types is controlled by a set of environmental factors such as climate, organisms, parent material and topography as well as time and space. A change of these factors will lead to a change in the spatial distribution of soil types. In this study, we use a digital soil mapping approach to improve our knowledge about major soil type distributing factors in the steppe regions of Inner Mongolia (China) which currently undergo tremendous environmental change, e.g. climate and land use change. We use Random Forests in an effort to map Reference Soil Groups according to the World Reference Base for Soil Resources (WRB) in the Xilin River catchment. We benefit from the superior prediction capabilities of RF and additional interpretive results in order to identify the major environmental factors that control spatial patterns of soil types. The nine WRB soil groups that were identified and spatially predicted for the study area are Arenosol, Calcisol, Cambisol, Chernozem, Cryosol, Gleysol, Kastanozem, Phaeozem and Regosol.
Model and prediction performances of the RF model are high with an Out-of-Bag error of 51.6% for the model and a misclassification error for the predicted map of 28.9%. The main controlling factors of soil type distribution are land use, a set of topographic variables, geology and climate. However, land use and climate are of major importance and topography and geology are of minor importance. The visualizations of the predictions, the variable importance measures as result of RF and the comparisons of these with the spatial distribution of the environmental factors delivered additional, quantitative information of these controlling factors and revealed that intensively grazed areas are subjected to soil degradation. However, most of the area is still governed by natural soil forming processes which are driven by climate, topography and geology. Most importantly though, our study revealed that a shift towards warmer temperatures and lower precipitation regimes will lead to a change of the spatial distribution of RSGs towards steppe soils that store less carbon, i.e. a decrease of spatial extent of Phaeozems and an increase of spatial extent of Chernozems and Kastanozems.
In the last decade growing interest has emerged in quantifying the spatial and temporal variations in mountain building. Until recently, insufficient data have been available to attempt such a task at the scale of large orogens such as the Himalaya. The Himalaya accommodates ongoing convergence between India and Eurasia and is a focal point for studying orogen evolution and hypothesized interactions between tectonics and climate. Here we integrate 1126 published bedrock mineral cooling ages with a transient 1D Monte-Carlo thermal-kinematic erosion model to quantify the denudation histories along similar to 2700 km of the Himalaya. The model free parameter is a temporally variable denudation rate from 50 Ma to present. Thermophysical material properties and boundary conditions were tuned to individual study areas. Monte-Carlo simulations were conducted to identify the range of denudation histories that can reproduce the observed cooling ages. Results indicate large temporal and spatial variations in denudation and these are resolvable across different tectonic units of the Himalaya. More specifically, across > 1000 km of the southern Greater Himalaya denudation rates were highest (similar to 1.5-3 mm/yr) between similar to 10 and 2 Ma and lower (0.5-2.6 mm/yr) over the last 2 My. These differences are best determined in the NW-Himalaya. In contrast to this, across the similar to 2500 km length of the northern Greater Himalaya denudation rates vary over length scales of similar to 300-1700 km. Slower denudation (<1 mm/yr) occurred between 10 and 4 Ma followed by a large increase (1.2-2.6 mm/yr) in the last similar to 4 Ma. We find that only the southern Greater Himalayan Sequence clearly supports a continuous co-evolution of tectonics, climate and denudation. Results from the higher elevation northern Greater Himalaya suggest either tectonic driven variations in denudation due to a ramp-flat geometry in the main decollement and/or recent glacially enhanced denudation.
The northward motion of the Pamir indenter with respect to Eurasia has resulted in coeval thrusting, strike-slip faulting, and normal faulting. The eastern Pamir is currently deformed by east-west oriented extension, accompanied by uplift and exhumation of the Kongur Shan (7719m) and Muztagh Ata (7546m) gneiss domes. Both domes are an integral part of the footwall of the Kongur Shan extensional fault system (KES), a 250 km long, north-south oriented graben. Why active normal faulting within the Pamir is primarily localized along the KES and not distributed more widely throughout the orogen has remained unclear. In addition, relatively little is known about how deformation has evolved throughout the Cenozoic, despite refined estimates on present-day crustal deformation rates and microseismicity, which indicate where crustal deformation is presently being accommodated. To better constrain the spatiotemporal evolution of faulting along the KES, we present 39 new apatite fission track, zircon U-Th-Sm/He, and Ar-40/Ar-39 cooling ages from a series of footwall transects along the KES graben shoulder. Combining these data with present-day topographic relief, 1-D thermokinematic and exhumational modeling documents successive stages, rather than synchronous deformation and gneiss dome exhumation. While the exhumation of the Kongur Shan commenced during the late Miocene, extensional processes in the Muztagh Ata massif began earlier and have slowed down since the late Miocene. We present a new model of synorogenic extension suggesting that thermal and density effects associated with a lithospheric tear fault along the eastern margin of the subducting Alai slab localize extensional upper plate deformation along the KES and decouple crustal motion between the central/western Pamir and eastern Pamir/Tarim basin.
Architectural analysis of the Late Cretaceous alveolinaceans of the Caribbean palaeobioprovince has made it possible to separate four genera: Praechubbina, Chubbinella gen. nov., Chubbina and Caribalveolina. The first three genera belong to the family Rhapydioninidae, while the fourth is placed in the family Alveolinidae. Two species, Praechubbina breviclaustra and P. oxchucensis sp. nov., represent the primitive genus Praechubbina, while the species cardenasensis and obesa, previously ascribed to this genus, must be reassigned respectively to Chubbinella gen. nov. and Caribalveolina. The species Chubbina jamaicensis, C. macgillavryi and C. fourcadei sp. nov. complete the inventory of Chubbina. The alveolinid genus Caribalveolina comprises two species, C. obesa and C. michaudi. Caribbean alveolinaceans include two successive assemblages. The lower assemblage is characterized by Praechubbina oxchucensis, P. brevisclaustra, Chubbinella cardenasensis and Caribalveolina obesa. The upper assemblage is represented by the genus Chubbina, with C. fourcadei, C. jamaicensis and C. macgillavryi, and Caribalveolina michaudi. The age of the lower assemblage is uncertain (probably Late CampanianEarly Maastrichtian), while the upper assemblage has been dated by strontium isotope stratigraphy as Late Maastrichtian.
A new occurrence of eclogites was found in the Kesandere valley in the eastern most part of the Bitlis complex, SE Anatolia. These high-pressure (HP) relics were preserved in calc-arenitic metasediments within the high-grade metamorphic basement of the Bitlis complex. The eclogitic parageneses were strongly overprinted during decompression and heating. These new eclogites locality complements the evidence of blueschist-facies metamorphism documented recently in the meta-sedimentary cover sequence of this part of the Bitlis complex. Thermodynamic calculations suggest peak conditions of ca. 480-540 degrees C/1.9-2.4GPa. New U/Pb dates of 84.4 +/-.9 and 82.4 +/-.9Ma were obtained on zircons from two Kesandere eclogite samples. On the basis of geochemical criteria, these dates are interpreted to represent zircon crystallization during the eclogitic peak stage. Kesandere eclogites differ from those previously described in the western Bitlis complex (Mt. Gablor locality) in terms of lithologic association, protolithic origin, and peak P-T conditions (600-650 degrees C/1.0-2.0GPa, respectively). On the other hand, eclogitic metamorphism of Kesandere metasediments occurred shortly before blueschist-facies metamorphism of the sedimentary cover (79-74Ma Ar-40/Ar-39 white mica). Therefore, the exhumation of Kesandere eclogites started between ca. 82 and 79Ma, while the meta-sedimentary cover was being buried. During this short time span, Kesandere eclogite were likely uplifted from similar to 65 to 35km depth, indicating a syn-subduction exhumation rate of similar to 4.3mm/a. Subsequently, eclogite- and blueschist-facies rocks were likely retrogressed contemporarily during collision-type metamorphism (around 72-69Ma). The Bitlis HP rocks thus sample a subduction zone that separated the Bitlis-Puturge (Bistun?) block from the South-Armenian block, further north. To the south, Eocene metasediments of the Urse formation are imbricated below the Bitlis complex. They contain (post Eocene) blueschists, testifying separation from the Arabian plate and southward migration of the subduction zone. The HT overprint of Kesandere eclogites can be related to the asthenospheric flow provoked by subducting slab retreat or break off.
This study presents a reconstruction of the Late Holocene climate in Kamchatka based on chironomid remains from a 332 cm long composite sediment core recovered from Dvuyurtochnoe Lake (Two-Yurts Lake, TYL) in central Kamchatka. The oldest recovered sediments date to about 4500 cal years BP. Chironomid head capsules from TYL reflect a rich and diverse fauna. An unknown morphotype of Tanytarsini, Tanytarsus type klein, was found in the lake sediments. Our analysis reveals four chironomid assemblage zones reflecting four different climatic periods in the Late Holocene. Between 4500 and 4000 cal years BP, the chironomid composition indicates a high lake level, well-oxygenated lake water conditions and close to modern temperatures (similar to 13 degrees C). From 4000 to 1000 cal years BP, two consecutive warm intervals were recorded, with the highest reconstructed temperature reaching 16.8 degrees C between 3700 and 2800 cal years BP. Cooling trend, started around 1100 cal years BP led to low temperatures during the last stage of the Holocene. Comparison with other regional studies has shown that termination of cooling at the beginning of late Holocene is relatively synchronous in central Kamchatka, South Kurile, Bering and Japanese Islands and take place around 3700 cal years BP. From ca 3700 cal years BP to the last millennium, a newly strengthened climate continentality accompanied by general warming trend with minor cool excursions led to apparent spatial heterogeneity of climatic patterns in the region. Some timing differences in climatic changes reconstructed from chironomid record of TYL sediments and late Holocene events reconstructed from other sites and other proxies might be linked to differences in local forcing mechanisms or caused by the different degree of dating precision, the different temporal resolution, and the different sensitive responses of climate proxies to the climate variations. Further high-resolution stratigraphic studies in this region are needed to understand the spatially complex pattern of climate change in Holocene in Kamchatka and the surrounding region.
Leaf wax n-alkanes of terrestrial plants are long-chain hydrocarbons that can persist in sedimentary records over geologic timescales. Since meteoric water is the primary source of hydrogen used in leaf wax synthesis, the hydrogen isotope composition (delta D value) of these biomarkers contains information on hydrological processes. Consequently, leaf wax n-alkane delta D values have been advocated as powerful tools for paleohydrological research. The exact kind of hydrological information that is recorded in leaf wax n-alkanes remains, however, unclear because critical processes that determine their delta D values have not yet been resolved. In particular the effects of evaporative deuterium (D)-enrichment of leaf water on the delta D values of leaf wax n-alkanes have not yet been directly assessed and quantified. Here we present the results of a study where we experimentally tested if and by what magnitude evaporative D-enrichment of leaf water affects the delta D of leaf wax n-alkanes in angiosperm C3 and C4 plants. Our study revealed that n-alkane delta D values of all plants that we investigated were affected by evaporative D-enrichment of leaf water. For dicotyledonous plants we found that the full extent of leaf water evaporative D-enrichment is recorded in leaf wax n-alkane delta D values. For monocotyledonous plants we found that between 18% and 68% of the D-enrichment in leaf water was recorded in the delta D values of their n-alkanes. We hypothesize that the different magnitudes by which evaporative D-enrichment of leaf water affects the delta D values of leaf wax n-alkanes in monocotyledonous and dicotyledonous plants is the result of differences in leaf growth and development between these plant groups. Our finding that the evaporative D-enrichment of leaf water affects the delta D values of leaf wax n-alkanes in monocotyledonous and dicotyledonous plants albeit at different magnitudes - has important implications for the interpretation of leaf wax n-alkane delta D values from paleohydrological records. In addition, our finding opens the door to employ delta D values of leaf wax n-alkanes as new ecohydrological proxies for evapotranspiration that can be applied in contemporary plant and ecosystem research.
During the last glacial period, the North Atlantic region experienced pronounced, millennial-scale alternations between cold, stadial conditions and milder interstadial conditions-commonly referred to as Dansgaard-Oeschger oscillations-as well as periods of massive iceberg discharge known as Heinrich events(1). Changes in Northern Hemisphere temperature, as recorded in Greenland(2-4), are thought to have affected the location of the Atlantic intertropical convergence zone(5,6) and the strength of the Indian summer monsoon(7,8). Here we use high-resolution records of sediment colour-a measure of terrigenous versus biogenic content-from the Cariaco Basin off the coast of Venezuela and the Arabian Sea to assess teleconnections with the North Atlantic climate system during the last glacial period. The Cariaco record indicates that the intertropical convergence zone migrated seasonally over the site during mild stadial conditions, but was permanently displaced south of the basin during peak stadials and Heinrich events. In the Arabian Sea, we find evidence of a weak Indian summer monsoon during the stadial events. The tropical records show a more variable response to North Atlantic cooling than the Greenland temperature records. We therefore suggest that Greenland climate is especially sensitive to variations in the North Atlantic system-in particular sea-ice extent-whereas the intertropical convergence zone and Indian monsoon system respond primarily to variations in mean Northern Hemisphere temperature.
This study examines patterns of climate variability by mapping shoreline changes between 1973 and 2008 for two shallow lakes in Malawi, East Africa. Multi-temporal LANDSAT data covering eight different years within the period of investigation were utilised for lake-area mapping, using image classification techniques. The approach was verified using simple comparisons with local rainfall data and satellite altimetry data. Results indicated that the lake areas varied between the different years investigated and that, although the lakes were affected by the same climate-forcing mechanisms, the individual basin characteristics had a critical effect on their responses. The most likely drivers for the climate-related shoreline variations are the El Nino/Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), causing synchronous changes to the water levels in both lakes, albeit showing differences in climate signal amplification.
The Shanderman eclogites and related metamorphosed oceanic rocks mark the site of closure of the Palaeotethys ocean in northern Iran. The protolith of the eclogites was an oceanic tholeiitic basalt with MORB composition. Eclogite occurs within a serpentinite matrix, accompanied by mafic rocks resembling a dismembered ophiolite. The eclogitic mafic rocks record different stages of metamorphism during subduction and exhumation. Minerals formed during the prograde stages are preserved as inclusions in peak metamorphic garnet and omphacite. The rocks experienced blueschist facies metamorphism on their prograde path and were metamorphosed in eclogite facies at the peak of metamorphism. The peak metamorphic mineral paragenesis of the rocks is omphacite, garnet (pyrope-rich), glaucophane, paragonite, zoisite and rutile. Based on textural relations, post-peak stages can be divided into amphibolite and greenschist facies. Pressure and temperature estimates for eclogite facies minerals (peak of metamorphism) indicate 15-20kbar at similar to 600 degrees C. The pre-peak blueschist facies assemblage yields <11kbar and 400-460 degrees C. The average pressure and temperature of the post-peak amphibolite stage was 5-6kbar, similar to 470 degrees C. The Shanderman eclogites were formed by subduction of Palaeotethys oceanic crust to a depth of no more than 75km. Subduction was followed by collision between the Central Iran and Turan blocks, and then exhumation of the high pressure rocks in northern Iran.
Annually laminated (varved) lake sediments with intercalated detrital layers resulting from sedimentary input by runoff events are ideal archives to establish precisely dated records of past extreme runoff events. In this study, the mid- to late Holocene varved sediments of Lake Mondsee (Upper Austria) were analysed by combining sedimentological, geophysical and geochemical methods. This approach allows to distinguish two types of detrital layers related to different types of extreme runoff events (floods and debris flows) and to detect changes in flood activity during the last 7100 years. In total, 271 flood and 47 debris flow layers, deposited during spring and summer, were identified, which cluster in 18 main flood episodes (FE 1-18) with durations of 30-50 years each. These main flood periods occurred during the Neolithic (7100-7050 vyr BP and 6470-4450 vyr BP), the late Bronze Age and the early Iron Age (3300-3250 and 2800-2750 vyr BP), the late Iron Age (2050-2000 vyr BP), throughout the Dark Ages Cold Period (1500-1200 vyr BP), and at the end of the Medieval Warm Period and the Little Ice Age (810-430 vyr BP).
Summer flood episodes in Lake Mondsee are generally more abundant during the last 1500 years, often coinciding with major advances of Alpine glaciers. Prior to 1500 vyr BP, spring/summer floods and debris flows are generally less frequent, indicating a lower number of intense rainfall events that triggered erosion. In comparison with the increase of late Holocene flood activity in western and northwestern (NW) Europe, commencing already as early as 2800 yr BP, the hydro-meteorological shift in the Lake Mondsee region occurred much later. These time lags in the onset of increased hydrological activity might be either due to regional differences in atmospheric circulation pattern or to the sensitivity of the individual flood archives. The Lake Mondsee sediments represent the first precisely dated and several millennia long summer flood record for the northeastern (NE) Alps, a key region at the climatic boundary of Atlantic, Mediterranean and East European air masses, aiding a better understanding of regional and seasonal peculiarities of flood occurrence under changing climate conditions. (C) 2013 Elsevier Ltd. All rights reserved.
Any understanding of sediment routing from mountain belts to their forelands and offshore sinks remains incomplete without estimates of intermediate storage that decisively buffers sediment yields from erosion rates, attenuates water and sediment fluxes, and protects underlying bedrock from incision. We quantify for the first time the sediment stored in > 38000 mainly postglacial Himalayan valley fills, based on an empirical volume-area scaling of valley-fill outlines automatically extracted from digital topographic data. The estimated total volume of 690(+452/-242) km(3) is mostly contained in few large valley fills > 1 km(3), while catastrophic mass wasting adds another 177(31) km(3). Sediment storage volumes are highly disparate along the strike of the orogen. Much of the Himalaya's stock of sediment is sequestered in glacially scoured valleys that provide accommodation space for similar to 44% of the total volume upstream of the rapidly exhuming and incising syntaxes. Conversely, the step-like long-wave topography of the central Himalayas limits glacier extent, and thus any significant glacier-derived storage of sediment away from tectonic basins. We show that exclusive removal of Himalayan valley fills could nourish contemporary sediment flux from the Indus and Brahmaputra basins for > 1 kyr, though individual fills may attain residence times of > 100 kyr. These millennial lag times in the Himalayan sediment routing system may sufficiently buffer signals of short-term seismic as well as climatic disturbances, thus complicating simple correlation and interpretation of sedimentary archives from the Himalayan orogen, its foreland, and its submarine fan systems. (C) 2013 Elsevier B.V. All rights reserved.
Species distribution models are useful for identifying driving environmental factors that determine earthworm distributions as well as for predicting earthworm distribution patterns and abundances at different scales. However, due to large efforts in data acquisition, studies on larger scales are rare and often focus on single species or earthworms in general. In this study, we use boosted regression tree models (BRTs) for predicting the distribution of the three functional earthworm types, i.e. anecics, endogeics and epigeics, in an agricultural area in Baden-Wurttemberg (Southwest Germany).
First, we predicted presence and absence and later earthworm abundances, considering predictors depicting land management, topography, and soil conditions as well as biotic interaction by using the abundance of the other functional earthworm types. The final presence-absence models performed reasonably well, with explained deviances between 24 and 51% after crossvalidation. Models for abundances of anecics and endogeics were less successful, since the high small-scale variability and patchiness in earthworm abundance influenced the representativeness of the field measurements. This resulted in a significant model uncertainty, which is practically very difficult to overcome with earthworm sampling campaigns at the catchment scale.
Results showed that management practices (i.e. disturbances), topography, soil conditions, and biotic interactions with other earthworm groups are the most relevant predictors for spatial distribution (incidence) patterns of all three functional groups. The response curves and contributions of predictors differ for the three functional earthworm types. Epigeics are also controlled by topographic features, endogeics by soil parameters.
Fluid flow in low-permeable carbonate rocks depends on the density of fractures, their interconnectivity and on the formation of fault damage zones. The present-day stress field influences the aperture hence the transmissivity of fractures whereas paleostress fields are responsible for the formation of faults and fractures. In low-permeable reservoir rocks, fault zones belong to the major targets. Before drilling, an estimate for reservoir productivity of wells drilled into the damage zone of faults is therefore required. Due to limitations in available data, a characterization of such reservoirs usually relies on the use of numerical techniques. The requirements of these mathematical models encompass a full integration of the actual fault geometry, comprising the dimension of the fault damage zone and of the fault core, and the individual population with properties of fault zones in the hanging and foot wall and the host rock. The paper presents both the technical approach to develop such a model and the property definition of heterogeneous fault zones and host rock with respect to the current stress field. The case study describes a deep geothermal reservoir in the western central Molasse Basin in southern Bavaria, Germany. Results from numerical simulations indicate that the well productivity can be enhanced along compressional fault zones if the interconnectivity of fractures is lateral caused by crossing synthetic and antithetic fractures. The model allows a deeper understanding of production tests and reservoir properties of faulted rocks.
Multi-proxy dating of Holocene maar lakes and Pleistocene dry maar sediments in the Eifel, Germany
(2013)
During the last twelve years the ELSA Project (Eifel Laminated Sediment Archive) at Mainz University has drilled a total of about 52 cores from 27 maar lakes and filled-in maar basins in the Eifel/Germany. Dating has been completed for the Holocene cores using 6 different methods (Pb-210 and Cs-137 activities, palynostratigraphy, event markers, varve counting, C-14) In general, the different methods consistently complement one another within error margins. Event correlation was used for relating typical lithological changes with historically known events such as the two major Holocene flood events at 1342 AD and ca 800 BC. Dating of MIS2-MIS3 core sections is based on greyscale tuning, radiocarbon and OSL dating, magnetostratigraphy and tephrochronology. The lithological changes in the sediment cores demonstrate a sequence of events similar to the North Atlantic rapid climate variability of the Last Glacial Cycle. The warmest of the MIS3 interstadials was GI14, when a forest with abundant spruce covered the Eifel area from 55 to 48 ka BP, i.e. during a time when also other climate archives in Europe suggested very warm conditions. The forest of this "Early Stage 3 warm phase" developed subsequently into a steppe with scattered birch and pine, and finally into a glacial desert at around 25 ka BP. Evidence for Mono Lake and Laschamp geomagnetic excursions is found in two long cores. Several large eruptions during Middle and Late Pleistocene (Ulmener Maar - 11,000 varve years BP, Laacher See - 12,900 varve years BP, Mosenberg volcanoes/Meerfelder Maar 41-45 cal ka BP, Dumpel Maar 116 ka BP, Glees Maar - 151 ka BP) produced distinct ash-layers crucial for inter-core and inter-site correlations. The oldest investigated maar of the Eifel is Ar-40/Ar-39 dated to the time older than 520 ka BP.
The persistence of topography within ancient orogens remains one of the outstanding questions in landscape evolution. In the eastern North American Appalachians, this question is manifest in the outstanding problem of whether topographic relief is in a quasi-equilibrium state, decaying slowly over many millennia, or whether relief has increased during the late Cenozoic. Here we present quantitative geomorphic data from the nonglaciated portion of the Susquehanna River drainage basin that provide insight into these end-member models. Analysis of channel profiles draining upland catchments in the northern Valley and Ridge, Appalachian Plateau, Blue Ridge, and Piedmont provinces reveals that a large number of streams have well defined knickpoints clustered at 300-600 m elevation but not systematically associated with transitions from weak to resistant substrate. Cosmogenic Be-10 inventories of modern stream sediment indicate that erosion rates are spatially variable, ranging from similar to 5-30 m/Myr above knickpoints to similar to 50-100 m/Myr below knickpoints. Overall, channel gradients, normalized for drainage area, scale linearly with catchment-averaged erosion rates. Collectively, regionally consistent spatial relationships among erosion rate, channel steepness, and knickpoints reveal an ongoing wave of transient channel adjustment to a change in relative base level. Reconstructions of relict channel profiles above knickpoints suggest that higher rates of incision are associated with similar to 100-150 m of relative base level fall that accompanied epierogenic rock uplift rather than a change to a more erosive climate or drainage reorganization. Channel response timescales imply that the onset of relative base level change predates similar to 3.5 Ma and may have begun as early as similar to 15 Ma. We suggest that adjustment of the channel network was likely driven by changes in mantle dynamics along the eastern seaboard of North America during the Neogene.
The multiple high-pressure (HP), low-temperature (LT) metamorphic units of Western and Central Anatolia offer a great opportunity to investigate the subduction-and continental accretion-related evolution of the eastern limb of the long-lived Aegean subduction system. Recent reports of the HP-LT index mineral Fe-Mg-carpholite in three metasedimentary units of the Gondwana-derived Anatolide-Tauride continental block (namely the Afyon Zone, the Oren Unit and the southern Menderes Massif) suggest a more complicated scenario than the single-continental accretion model generally put forward in previous studies. This study presents the first isotopic dates (white mica Ar-40-Ar-39 geochronology), and where possible are combined with P-T estimates (chlorite thermometry, phengite barometry, multi-equilibrium thermobarometry), on carpholite-bearing rocks from these three HP-LT metasedimentary units. It is shown that, in the Afyon Zone, carpholite-bearing assemblages were retrogressed through greenschist-facies conditions at c. 67-62 Ma. Early retrograde stages in the Oren Unit are dated to 63-59 Ma. In the Kurudere-Nebiler Unit (HP Mesozoic cover of the southern Menderes Massif), HP retrograde stages are dated to c. 45 Ma, and post-collisional cooling to c. 26 Ma. These new results support that the Oren Unit represents the westernmost continuation of the Afyon Zone, whereas the Kurudere-Nebiler Unit correlates with the Cycladic Blueschist Unit of the Aegean Domain. In Western Anatolia, three successive HP-LT metamorphic belts thus formed: the northernmost Tavsanli Zone (c. 88-82 Ma), the Oren-Afyon Zone (between 70 and 65 Ma), and the Kurudere-Nebiler Unit (c. 52-45 Ma). The southward younging trend of the HP-LT metamorphism from the upper and internal to the deeper and more external structural units, as in the Aegean Domain, points to the persistence of subduction in Western Anatolia between 93-90 and c. 35 Ma. After the accretion of the Menderes-Tauride terrane, in Eocene times, subduction stopped, leading to continental collision and associated Barrovian-type metamorphism. Because, by contrast, the Aegean subduction did remain active due to slab roll-back and trench migration, the eastern limb (below Southwestern Anatolia) of the Hellenic slab was dramatically curved and consequently teared. It therefore is suggested that the possibility for subduction to continue after the accretion of buoyant (e.g. continental) terranes probably depends much on palaeogeography.
From the Middle Eocene to Early Oligocene, the Earth experienced the most significant climatic cooling of the Cenozoic era. The Eocene-Oligocene transition (EOT) represents the culmination of this climatic cooling, leading to the onset of the Antarctic glaciation and, consequently, to the beginning of the present-day icehouse world. Whereas the response of deep-sea systems to this climate transition has been widely studied, its impact on the shallow-water carbonate realm is poorly constrained. Here, the sedimentary expression of the EOT in two shallow-marine carbonate successions (Nago and San Valentino, northern Italy) belonging to the Calcare di Nago Formation is presented. The chronostratigraphic framework was constructed by integrating litho-, bio-, and isotope-stratigraphic data (C and Sr isotopes), allowing to correlate these shallow-marine successions with pelagic sections in central Italy (Massignano), Tanzania (TOP Sites 12 and 17), and the Indian Ocean (ODP Site 744). Within several sections in northern Italy, including Nago and San Valentino, a Priabonian (Late Eocene) transgression is recorded. Oxygen isotopes of ODP Site 744 show a coeval negative shift of 0.4 parts per thousand., suggesting a glacio-eustatic origin for this transgression. In the Nago and San Valentino sections, no prominent sequence boundary has been detected that would indicate a rapid sea-level drop occurring together with the positive shift in delta O-18 defining the EOT-1 cooling event. Instead, a gradual shallowing of the depositional environment is observed. At TDP Sites 12 and 17, the EOT-1 is followed by a negative shift in delta O-18 of around 0.4 parts per thousand, which correlates with a relative deepening of the environment in the studied sections and suggests a melting pulse between EOT-1 and the Oligocene isotope event 1 (Oi-1). The positive delta O-18 shift related to the Oi-1 translates in San Valentino into a change in carbonate factory from a photozoan association dominated by larger benthic foraminifera, corals, and red algae to a heterozoan association dominated by bryozoans. The same bryozoan fades occurs in several Italian localities near the Eocene-Oligocene boundary. This fades is interpreted to represent an analogue of modern cool-water carbonates and results from a cooling pulse of at least regional scale, associated to the Oi-1 event.
Vertical flow systems filled with porous medium have been shown to efficiently remove volatile organic contaminants (VOCs) from contaminated groundwater. To apply this semi-natural remediation strategy it is however necessary to distinguish between removal due to biodegradation and due to volatile losses to the atmosphere. Especially for (potentially) toxic VOCs, the latter needs to be minimized to limit atmospheric emissions. In this study, numerical simulation was used to investigate quantitatively the removal of volatile organic compounds in two pilot-scale water treatment systems: an unplanted vertical flow filter and a planted one, which could also be called a vertical flow constructed wetland, both used for the treatment of contaminated groundwater. These systems were intermittently loaded with contaminated water containing benzene and MTBE as main VOCs. The highly dynamic but permanently unsaturated conditions in the porous medium facilitated aerobic biodegradation but could lead to volatile emissions of the contaminants. Experimental data from porous material analyses, flow rate measurements, solute tracer and gas tracer test, as well as contaminant concentration measurements at the boundaries of the systems were used to constrain a numerical reactive transport modeling approach. Numerical simulations considered unsaturated water flow, transport of species in the aqueous and the gas phase as well as aerobic degradation processes, which made it possible to quantify the rates of biodegradation and volatile emissions and calculating their contribution to total contaminant removal. A range of degradation rates was determined using experimental results of both systems under two operation modes and validated by field data obtained at different operation modes applied to the filters. For both filters, simulations and experimental data point to high biodegradation rates, if the flow filters have had time to build up their removal capacity. For this case volatile emissions are negligible and total removal can be attributed to biodegradation, only. The simulation study thus supports the use of both of these vertical flow systems for the treatment of groundwater contaminated with VOCs and the use of reactive transport modeling for the assessment of VOCs removal and operation modes in these high performance treatment systems.
The northern part of the Pamir orogen is the preeminent example of an active intracontinental subduction zone in the early stages of continent-continent collision. Such zones are the least understood type of plate boundaries because modern examples are few and of limited access, and ancient analogs have been extensively overprinted by subsequent tectonic and erosion processes. In the Pamir, it has been assumed that most of the plate convergence was accommodated by overthrusting along the plate-bounding Main Pamir Thrust (MPT), which forms the principal northern mountain and deformation front of the Pamir. However, the synopsis of our new and previously published thermochronologic data from this region shows that the hanging wall of the MPT experienced relatively minor amounts of late Cenozoic exhumation. The Pamir orogen as a whole is an integral part of the overriding plate in a subduction system, while the remnant basin to the north constitutes the downgoing plate, with the bulk of the convergence accommodated by underthrusting. Herein, we demonstrate that the observed deformation of the upper and lower plates within the Pamir-Alai convergence zone resembles highly arcuate oceanic subduction systems characterized by slab rollback, subduction erosion, subduction accretion, and marginal slab-tear faults. We suggest that the curvature of the North Pamir is genetically linked to the short width and rollback of the south-dipping Alai slab; northward motion (indentation) of the Pamir is accommodated by crustal processes related to this rollback. The onset of south-dipping subduction is tentatively linked to intense Pamir contraction following break-off of the north-dipping Indian slab beneath the Karakoram.
We perform a systematic study of all cities in Europe to assess the Urban Heat Island (UHI) intensity by means of remotely sensed land surface temperature data. Defining cities as spatial clusters of urban land cover, we investigate the relationships of the UHI intensity, with the cluster size and the temperature of the surroundings. Our results show that in Europe, the UHI intensity in summer has a strong correlation with the cluster size, which can be well fitted by an empirical sigmoid model. Furthermore, we find a novel seasonality of the UHI intensity for individual clusters in the form of hysteresis-like curves. We characterize the shape and identify apparent regional patterns.
Ostracod distribution and habitat relationships in the Kunlun Mountains, northern Tibetan Plateau
(2013)
Surface sediment samples were collected from the lakes Heihai, Kusai, Haiding Nuur and Yan Hu, and from streams and ponds in the Kunlun Mountains at the northern margin of the Tibetan Plateau to investigate the sub-fossil ostracod (micro-crustacean) fauna of the region. Among 65 collected samples, 46 ostracod shell-rich samples were used to study the relationship between the ostracod distribution and specific conductivity (SC) of the water, which ranged from 0.6 to 53.0 mS cm(-1). A total of eleven ostracod species was identified from this region, with about half of the species restricted to the Tibetan Plateau and its adjacent mountain areas, and the other half representing Holarctic taxa. Tonnacypris cf. estonica and Tonnacypris tonnensis are reported from the Tibetan Plateau for the first time. Leucocythere sp. is the dominant species and Ilyocypris cf. bradyi is also relatively abundant. The other seven species were recorded with limited abundances apparently due to lower SC tolerances. Leucocythere sp. was recorded over the full SC range from 0.6 to 53 mS cm(-1). Eucypris mareotica is a typical brackish and saline water species, which was found at sample sites with high SC (2.8-53.0 mS cm(-1)). In contrast, Leucocythere dorsotuberosa, Candona candida and Eucypris afghanistanensis prefer freshwater to slightly oli-gohaline waters with SC < 1.8 mS cm(-1). The SC optimum and tolerance range for each species were determined and compared to earlier reported data from other regions of Central Asia. The results indicate that species assemblage data from fossil ostracod shells have a large potential to provide information on past SC levels and more general climate-determined moisture conditions. (C) 2013 Elsevier Ltd and INQUA. All rights reserved.
Considerable effort has been devoted to the development of simulation algorithms for facies modeling, whereas a discussion of how to combine those techniques has not existed. The integration of multiple geologic data into a three-dimensional model, which requires the combination of simulation techniques, is yet a current challenge for reservoir modeling. This article presents a thought process that guides the acquisition and modeling of geologic data at various scales. Our work is based on outcrop data collected from a Jurassic carbonate ramp located in the High Atlas mountain range of Morocco. The study window is 1 km (0.6 mi) wide and 100 m (328.1 ft) thick. We describe and model the spatial and hierarchical arrangement of carbonate bodies spanning from largest to smallest: (1) stacking pattern of high-frequency depositional sequences, (2) facies association, and (3) lithofacies. Five sequence boundaries were modeled using differential global position system mapping and light detection and ranging data. The surface-based model shows a low-angle profile with modest paleotopographic relief at the inner-to-middle ramp transition. Facies associations were populated using truncated Gaussian simulation to preserve ordered trends between the inner, middle, and outer ramps. At the lithofacies scale, field observations and statistical analysis show a mosaiclike distribution that was simulated using a fully stochastic approach with sequential indicator simulation.
This study observes that the use of one single simulation technique is unlikely to correctly model the natural patterns and variability of carbonate rocks. The selection and implementation of different techniques customized for each level of the stratigraphic hierarchy will provide the essential computing flexibility to model carbonate settings. This study demonstrates that a scale-dependent modeling approach should be a common procedure when building subsurface and outcrop models.
The Tibetan Plateau (TP), including its surrounding mountain ranges, represents the largest store of ice outside the polar regions. It hosts numerous lakes as well as the head waters of major Asian rivers, on which billions of people depend, and it is particularly sensitive to climate change. The moisture transport to the TP is controlled by the Indian and Pacific monsoon and the Westerlies. Understanding the evolution of the interaction of these circulation systems requires studies on climate archives in different spatial and temporal contexts. The objective of this study is to learn more about the interannual variability of precipitation patterns across the TP and how different hydrologic systems react to different climatic factors.
Aragonite shells of the aquatic gastropod Radix, which is widely distributed in the region, may represent suitable archives for inferring hydrologic and climatic signals in particularly high resolution. Therefore, sclerochronological studies of delta O-18 and delta C-13 ratios in Radix shells from seven lakes were conducted, each representing a different hydrologic and climatic setting, on a transect from the Pamirs across the TP.
The shell patterns exhibit an increasing influence of precipitation and a decreasing influence of evaporation on the isotope compositions from west to east. delta O-18 values of shells from lakes on the eastern and central TP (Donggi Cona, Yamdrok Yumco, Tarab Co) mirror monsoon signals, indicated by more negative values and higher variabilities compared to the more western lakes (Karakul, Bangong/Nyak, Manasarovar). In Yadang Co, located on the central southern TP, the monsoon rains did not reach the lake in the sampling year, although it is located in a region which is usually affected by monsoon circulation. The delta O-18 values are used to differentiate the annual hydrological cycle into ice cover period, melt water period, precipitation period and evaporation period. delta C-13 compositions in the shells particularly depend on specific habitats, which vary in biological productivity and in carbon sources. delta O-18 and delta C-13 patterns show a positive covariance in shells originating from large closed basins. The results show that Radix shells mirror general climatic differences between the seven lake regions. These differences reflect both regional and local climate signals in sub-seasonal resolution, without noticeable dependence on the particular lake system.
Palaeoenvironmental implications of evaporative gaylussite crystals from Lonar Lake, central India
(2013)
We have undertaken petrographic, mineralogical, geochemical and isotopic investigations on carbonate minerals found within a 10-m-long core from Lonar Lake, central India, with the aim of evaluating their potential as palaeoenvironmental proxies. The core encompasses the entire Holocene and is the first well-dated high-resolution record from central India. While calcite and/or aragonite were found throughout the core, the mineral gaylussite was found only in two specific intervals (46303890 and 2040560 cal a BP). Hydrochemical and isotope data from inflowing streams and lake waters indicate that evaporitic processes play a dominant role in the precipitation of carbonates within this lake. Isotopic (18O and 13C) studies on the evaporative gaylussite crystals and residual bulk carbonates (calcite) from the long core show that evaporation is the major control on 18O enrichment in both the minerals. However, in case of 13C additional mechanisms, for example methanogenesis (gaylussite) and phytoplankton productivity (calcium carbonate), play an additional important role in some intervals. We also discuss the relevance of our investigation for palaeoclimate reconstruction and late Holocene monsoon variability.
Raman microspectroscopy on carbonaceous material (RSCM) from the eastern Tauern Window indicates contrasting peak-temperature patterns in three different fabric domains, each of which underwent a poly-metamorphic orogenic evolution: Domain 1 in the northeastern Tauern Window preserves oceanic units (Glockner Nappe System, Matrei Zone) that attained peak temperatures (T-p) of 350-480 degrees C following Late Cretaceous to Palaeogene nappe stacking in an accretionary wedge. Domain 2 in the central Tauern Window experienced T-p of 500-535 degrees C that was attained either within an exhumed Palaeogene subduction channel or during Oligocene Barrovian-type thermal overprinting within the Alpine collisional orogen. Domain 3 in the Eastern Tauern Subdome has a peak-temperature pattern that resulted from Eo-Oligocene nappe stacking of continental units derived from the distal European margin. This pattern acquired its presently concentric pattern in Miocene time due to post-nappe doming and extensional shearing along the Katschberg Shear Zone System (KSZS). T-p values in the largest (Hochalm) dome range from 612 degrees C in its core to 440 degrees C at its rim. The maximum peak-temperature gradient (70 degrees Ckm(-1)) occurs along the eastern margin of this dome where mylonitic shearing of the Katschberg Normal Fault (KNF) significantly thinned the Subpenninic- and Penninic nappe pile, including the pre-existing peak-temperature gradient.
The Tuz Golu Basin is the largest sedimentary depression located at the center of the Central Anatolian Plateau, an extensive, low-relief region with elevations of ca. 1 km located between the Pontide and Tauride mountains. Presently, the basin morphology and sedimentation processes are mainly controlled by the extensional Tuz Golu Fault Zone in the east and the transtensional Inonu-Eskisehir Fault System in the west. The purpose of this study is to contribute to the understanding of the Plio-Quaternary deformation history and to refine the timing of the latest extensional phase of the Tuz Golu Basin. Field observations, kinematic analyses, interpretations of seismic reflection lines, and Ar-40/Ar-39 dating of a key ignimbrite layer suggest that a regional phase of NNW-SSE to NE-SW contraction ended by 6.81 +/- 0.24 Ma and was followed by N-S to NE-SW extension during the Pliocene-Quaternary periods. Based on sedimentological and chronostratigraphic markers, the average vertical displacement rates over the past 5 or 3 Ma with respect to the central part of Tuz Golu Lake are 0.03 to 0.05 mm/year for the fault system at the western flank of the basin and 0.08 to 0.13 mm/year at the eastern flank. Paleo-shorelines of the Tuz Golu Lake, vestiges of higher lake levels related to Quaternary climate change, are important strain markers and were formed during Last Glacial Maximum conditions as indicated by a radiocarbon age of 21.8 +/- 0.4 ka BP obtained from a stromatolitic crust. Geomorphic observations and deformed lacustrine shorelines suggest that the main strand of the Tuz Golu Fault Zone straddling the foothills of the Sereflikochisar-Aksaray range has not been active during the Holocene. Instead, deformation appears to have migrated towards the interior of the basin along an offshore fault that runs immediately west of Sereflikochisar Peninsula. This basinward migration of deformation is probably associated with various processes acting at the lithospheric scale, such as plateau uplift and/or microplate extrusion.
Preface to the special issue "Triggered and induced seismicity: probabilities and discrimination"
(2013)
A general increase in precipitation has been observed in Germany in the last century, and potential changes in flood generation and intensity are now at the focus of interest. The aim of the paper is twofold: a) to project the future flood conditions in Germany accounting for various river regimes (from pluvial to nival-pluvial regimes) and under different climate scenarios (the high, A2, low, B1, and medium, A1B, emission scenarios) and b) to investigate sources of uncertainty generated by climate input data and regional climate models. Data of two dynamical Regional Climate Models (RCMs), REMO (REgional Model) and CCLM (Cosmo-Climate Local Model), and one statistical-empirical RCM, Wettreg (Wetterlagenbasierte Regionalisierungsmethode: weather-type based regionalization method), were applied to drive the eco-hydrological model SWIM (Soil and Water Integrated Model), which was previously validated for 15 gauges in Germany. At most of the gauges, the 95 and 99 percentiles of the simulated discharge using SWIM with observed climate data had a good agreement with the observed discharge for 1961-2000 (deviation within +/- 10 %). However, the simulated discharge had a bias when using RCM climate as input for the same period. Generalized Extreme Value (GEV) distributions were fitted to the annual maximum series of river runoff for each realization for the control and scenario periods, and the changes in flood generation over the whole simulation time were analyzed. The 50-year flood values estimated for two scenario periods (2021-2060, 2061-2100) were compared to the ones derived from the control period using the same climate models. The results driven by the statistical-empirical model show a declining trend in the flood level for most rivers, and under all climate scenarios. The simulations driven by dynamical models give various change directions depending on region, scenario and time period. The uncertainty in estimating high flows and, in particular, extreme floods remains high, due to differences in regional climate models, emission scenarios and multi-realizations generated by RCMs.
Quantifying lithogenic inputs to the North Pacific Ocean using the long-lived thorium isotopes
(2013)
Dissolved Th-232 is added to the ocean though the partial dissolution of lithogenic materials such as aerosol dust in the same way as other lithogenically sourced and more biologically important trace metals such as Fe. Oceanic Th-230, on the other hand, is sourced primarily from the highly predictable decay of dissolved U-234. The rate at which dissolved Th-232 is released by mineral dissolution can be constrained by a Th removal rate derived from Th-230:U-234 disequilibria, assuming steady-state. Calculated fluxes of dissolved Th-232 can in turn be used to estimate fluxes of other lithogenically sourced dissolved metals as well as the original lithogenic supplies, such as aerosol dust deposition, given the concentration and fractional solubility of Th (or other metals) in the lithogenic material. This method is applied to 7 water column profiles from the Innovative North Pacific Experiment (INOPEX) cruise of 2009 and 2 sites from the subtropical North Pacific. The structure of shallow depth profiles suggests rapid scavenging at the surface and at least partial regeneration of dissolved Th-232 at 100-200 m depth. This rapid cycling could involve colloidal Th generated during mineral dissolution, which may not be subject to the same removal rates as the more truly dissolved Th-230. An additional deep source of Th-232 was revealed in deep waters, most likely dissolution of seafloor sediments, and offers a constraint on dissolved trace element supply due to boundary exchange. (C) 2013 Elsevier B.V. All rights reserved.
The internal geological structure of the Northeast German Basin (NEGB) is affected by intense salt diapirism and by the presence of several stratified aquifer complexes of regional relevance. The shallow Quaternary to late Tertiary freshwater aquifer is separated from the underlying Mesozoic saline aquifers by an embedded Tertiary clay enriched aquitard (Rupelian Aquitard). An important feature of this aquitard is that hydraulic connections between the upper and lower aquifers do exist in areas where the Rupelian Aquitard is missing (hydrogeological windows). Three-dimensional thermohaline numerical simulations are carried out to investigate the effects of such hydrogeological windows in the Rupelian Aquitard on the resulting groundwater, temperature, and salinity distributions. Numerical results suggest that hydrogeological windows act as preferential domains of hydraulic interconnectivity between the different aquifers at depth and enable vigorous heat and mass transport which causes a mixing of warm and saline groundwater with cold and less saline groundwater within both aquifers. In areas where the Rupelian Aquitard confines the Mesozoic aquifer, dissolved solutes from major salt structures are transported laterally giving rise to plumes of variable salinity content ranging from few hundreds of meters to several tens of kilometers. Furthermore, destabilizing thermal buoyancy forces may overwhelm counteracting stabilizing salinity induced forces offside of salt domes. This may result in buoyant upward groundwater flow transporting heat and mass to shallower levels within the same Mesozoic Aquifer.
Various techniques are utilized by the seismological community, extractive industries, energy and geoengineering companies to identify earthquake nucleation processes in close proximity to engineering operation points. These operations may comprise fluid extraction or injections, artificial water reservoir impoundments, open pit and deep mining, deep geothermal power generations or carbon sequestration. In this letter to the editor, we outline several lines of investigation that we suggest to follow to address the discrimination problem between natural seismicity and seismic events induced or triggered by geoengineering activities. These suggestions have been developed by a group of experts during several meetings and workshops, and we feel that their publication as a summary report is helpful for the geoscientific community. Specific investigation procedures and discrimination approaches, on which our recommendations are based, are also published in this Special Issue (SI) of Journal of Seismology.
The Sierra de Aconquija and Cumbres Calchaquies in the thick-skinned northern Sierras Pampeanas, NW Argentina present an ideal setting to investigate the tectonically and erosionally controlled exhumation and uplift history of mountain ranges using thermochronological methods. Although these ranges are located along strike of one another, their spatiotemporal evolution varies significantly. Integrating modeled cooling histories constrained by K-Ar ages of muscovite and biotite, apatite fission track data as well as (U-Th)/He measurement of zircon and apatite reveal the structural evolution of these ranges beginning in the late stage of the Paleozoic Famatinian Orogeny. Following localized rift-related exhumation in the central part of the study area and slow erosion elsewhere, growth of the modern topography commenced in the Cenozoic during Andean deformation. The main activity occurred during the late Miocene, with varying magnitudes of rock uplift, surface uplift, and exhumation in the two mountain ranges. The Cumbres Calchaquies is characterized by a total of 5-7km of vertical rock uplift, around 3km of crestal surface uplift, and a maximum exhumation of 2-4km since that time. The Sierra de Aconquija experienced 10-13km of vertical rock uplift, similar to 4-5km of peak surface uplift, and 6-8km of exhumation since around 9Ma. Much of this exhumation occurred along a previously poorly recognized fault. Miocene reactivation of Cretaceous rift structures may explain along-strike variations within these ranges. Dating of sedimentary samples from adjacent basins supports the evolutionary model developed for the mountain ranges.
Astronomically tuned cyclic sedimentary successions provide unprecedented insight into the temporal evolution of depositional systems and major geologic events. However, placing astronomically calibrated records into an absolute time frame with confidence requires independent and precise geochronologic constraints. Astronomical tuning of the precessionally modulated sedimentary cycles of the Mediterranean Basin deposited during the Messinian Salinity Crisis (5.96-5.33 Ma) has indicated an similar to 90 k.y. "Messinian gap", corresponding to the evaporative drawdown of the Mediterranean following the closure of the Mediterranean-Atlantic gateway. In the Messinian deposits, a volcanic ash dated by Ar-40/Ar-39 geochronology was used to anchor the sedimentary cycles to the insolation curve. However, the uncertainty of the Ar-40/Ar-39 date introduces a potential two-cycle (similar to 40 k.y.) uncertainty in the tuning. Using high-precision chemical abrasion-thermal ionization mass spectrometry (CA-TIMS) U-Pb geochronology on single zircon grains from two Messinian ash layers in Italy, we obtained dates of 5.5320 +/- 0.0046 Ma and 5.5320 +/- 0.0074 Ma with sub-precessional resolution. Combined with our astronomical tuning of the Messinian Lower Evaporites, the results refine the duration of the "Messinian gap" to at most 28 or 58 +/- 9.6 k.y., which correlates with either the TG12 glacial interval alone, or both TG12 and TG14 glacial intervals, supporting the hypothesis of a glacio-eustatic contribution in fully isolating the Mediterranean from the Atlantic Ocean. Our new U-Pb dates also allow us to infer a precessionally modulated cyclicity for the post-evaporitic deposits, and hence enable us to tune those successions to the insolation curve.
The impact of land use changes on sustainable development is of increasing interest in many regions of the world. This study aimed to test the transferability of the Framework for Participatory Impact Assessment (FoPIA), which was originally developed in the European context, to developing countries, in which lack of data often prevents the use of data-driven impact assessment methods. The core aspect of FoPIA is the stakeholder-based assessment of alternative land use scenarios. Scenario impacts on regional sustainability are assessed by using a set of nine regional land use functions (LUFs), which equally cover the economic, social and environmental dimensions of sustainability. The cases analysed in this study include (1) the alternative spatial planning policies around the Merapi volcano and surrounding areas of Yogyakarta City, Indonesia; (2) the large-scale afforestation of agricultural areas to reduce soil erosion in Guyuan, China; (3) the expansion of soil and water conservation measures in the Oum Zessar watershed, Tunisia; (4) the agricultural intensification and the potential for organic agriculture in Bijapur, India; and (5) the land degradation and land conflicts resulting from land division and privatisation in Narok, Kenya. All five regions are characterised by population growth, partially combined with considerable economic development, environmental degradation problems and social conflicts. Implications of the regional scenario impacts as well as methodological aspects are discussed. Overall, FoPIA proved to be a useful tool for diagnosing regional human-environment interactions and for supporting the communication and social learning process among different stakeholder groups.
High applications of P fertilizers and manure are general practice in intensive agriculture and may cause eutrophication in adjacent streams. Bioavailability of P can be estimated by sequential extractions commonly used for soil or sediment. A single combined method may facilitate more effective comparisons of topsoils and adjoining stream sediments, and enhance management decisions. In this study, the suitability of an established soil P sequential extraction was tested on stream bed sediments. The study was conducted in the Sumas River watershed in the agricultural Lower Fraser Valley, Canada. Sediment samples with differing land use (forest, low and high intensity agriculture) from 1993, 1994, 2008, and 2009 from 14 sites along the Sumas River and tributaries were used. Total sequential extraction concentrations were in agreement with aqua regia digestion (Rs=0.96) and showed consistency over the study time sequence. P fractions released by 0.5 M NaHCO3 (median 14 %), 0.1 M NaOH (33 %), and 1.0 M HCl (38 %) were significantly (alpha=0.05) higher than P released by other extractants. These three extraction steps provide a practical and time-effective assessment of P lability in stream sediments and may be used as a combined scheme for sediment and soil. Analytical results further revealed that land use has a major and characteristic impact on P lability. With a land use change from forest to intensive agriculture, results showed an increase in total P concentrations (30 to 4,000 ppm) and in P lability, in particular for the moderately labile NaOH-P fraction (20 to 50 %).