Refine
Year of publication
- 2012 (169) (remove)
Document Type
- Article (142)
- Doctoral Thesis (17)
- Review (6)
- Preprint (2)
- Conference Proceeding (1)
- Master's Thesis (1)
Language
- English (169) (remove)
Is part of the Bibliography
- yes (169) (remove)
Keywords
- Holocene (5)
- climate change (4)
- Lake sediments (3)
- Wind erosion (3)
- Chile (2)
- Continental tectonics: strike-slip and transform (2)
- Erosion (2)
- Fernerkundung (2)
- Germany (2)
- Grassland (2)
- Maule earthquake (2)
- Monsoon (2)
- Ostracoda (2)
- Paleolimnology (2)
- Pollen (2)
- Random forests (2)
- Remote sensing (2)
- Sediment budget (2)
- Seismic tomography (2)
- Seismicity and tectonics (2)
- Stemflow (2)
- Throughfall (2)
- Tibetan Plateau (2)
- Water quality (2)
- XRD (2)
- Younger Dryas (2)
- erosion (2)
- paleoclimate (2)
- remote sensing (2)
- soil moisture (2)
- (U-Th)/He (1)
- AFT (1)
- Active tectonics (1)
- Actual evapotranspiration (1)
- Advanced Spaceborne Thermal Emission and Reflection Radiometer data (1)
- African Humid Period (1)
- Afyon Zone (1)
- Agglutinated foraminifera (1)
- Agro-meteorological data (1)
- Alas (1)
- Algeria (1)
- Alkalinity (1)
- Altiplano (1)
- Amazonia (1)
- Anisotrope Inversion (1)
- Anisotropie der Leitfähigkeit (1)
- Aquatic macrophytes (1)
- Ar dating (1)
- Ar-Ar white-mica dating (1)
- Aragonite (1)
- Archaean SCLM (1)
- Arctic (1)
- Aridity (1)
- Arkose (1)
- Arktis (1)
- Array seismology (1)
- Artificial neuronal network (1)
- Asia (1)
- Asian Summer Monsoon (1)
- Asteroid (1)
- Atlas Mountains (1)
- Babassu palm (Attalea speciosa Mart. synonym: Orbignya phalerata Mart.) (1)
- Barents Sea (1)
- Basin axial submarine channel (1)
- Biodiversity monitoring (1)
- Biomarker (1)
- Biomarkers (1)
- Bitlis complex (1)
- Bodenfeuchte (1)
- Boosted regression trees (1)
- Carbon and oxygen stable isotopes (1)
- Carbonate platforms (1)
- Catchment characteristics (1)
- Catchment classification (1)
- Central Anatolian plateau (1)
- Central Asia (1)
- Central Yakutia (1)
- Channel Transmission Losses (1)
- China (1)
- Classification trees (1)
- Climate change (1)
- Climate reconstruction (1)
- Coastal uplift (1)
- Computational fluid dynamics (1)
- Computational fluid dynamics (CFD) (1)
- Continental margins: transform (1)
- Controlled source seismology (1)
- Cooling rates (1)
- Correlation (1)
- Coseismic slip distribution (1)
- Cosmogenic nuclides (1)
- Crop type mapping (1)
- Cs-137 (1)
- DBH (1)
- Dead Sea Basin (1)
- Denudation (1)
- Diagenesis (1)
- Diatexites (1)
- Diatoms (1)
- Digital elevation model (1)
- Digital terrain analysis (1)
- Diol (1)
- Drainage networks (1)
- Dryland Rivers (1)
- Dust deposition (1)
- Dynamic behavior (1)
- ENSO (1)
- Early Paleogene (1)
- Early warning (1)
- Earthquake (1)
- Earthquake rates (1)
- Earthquakes (1)
- Earthworms (1)
- East African Rift (1)
- East African Rift System (1)
- Ebro basin (1)
- Ecological competition (1)
- Ecology (1)
- Ecosystem engineer (1)
- Edough (1)
- Electrical conductivity (1)
- Ellenberg indicator values (1)
- Entwicklungsländer (1)
- Environmental change (1)
- Environmental isotopes (1)
- Expert judgment (1)
- Extreme event (1)
- FEM (1)
- Feedback biotic-abiotic (1)
- Flood Forecasting (1)
- Flood forecasting (1)
- Fluorescence imaging (1)
- Folgenabschätzung (1)
- Frequency-magnitude distribution (1)
- Functional effect (1)
- Fuzzy (1)
- GIS (1)
- GPS (1)
- Gaylussite (1)
- Generalized linear models (1)
- Geobiology (1)
- Geomorphic indices (1)
- Gondwanaoberh (1)
- Ground vegetation (1)
- Ground-motion prediction equations (1)
- Ground-penetrating radar (1)
- Groundwater (1)
- Grt-Pyx exsolution (1)
- HP metamorphism (1)
- HT/LP metamorphism (1)
- Himalayan rivers (1)
- Himalayas (1)
- Hochwasservorhersage (1)
- Holocene thermal maximum (1)
- Human evolution (1)
- Humification (1)
- Hydrological Modelling (1)
- Hydrological extremes (1)
- Hydrological modelling (1)
- Hydropedology (1)
- Hypothesis generation (1)
- Iberian Basin (1)
- Impacts (1)
- In situ C-14 (1)
- Indian Ocean (1)
- Indian summer monsoon (1)
- Indische Sommer Monsun (1)
- Inference model (1)
- Intertidal organisms (1)
- Isomap (1)
- Jurassic (1)
- Kaghan Valley (1)
- Kenya (1)
- Kern-Mantel Grenze (1)
- Kettle holes (1)
- Klimarekonstruktion (1)
- Lake Turkana (1)
- Land use (1)
- Land use change (1)
- Landnutzung (1)
- Landscape planning (1)
- Landslide dam (1)
- Landslides (1)
- Late-Holocene (1)
- Latemar (1)
- Laurentide Ice Sheet (1)
- Leucocratic tourmaline orthogneisses (1)
- Lipid (1)
- Logic trees (1)
- Lonar lake (1)
- Lonarsee (1)
- Loppa High (1)
- Lower Cretaceous (1)
- Macerals (1)
- Magnetotellurik (1)
- Magnitude and frequency (1)
- Maturity (1)
- Maule (1)
- Maximum entropy method (1)
- Menderes Massif (1)
- Mesorbitolina (1)
- Meta-trachyandesite (1)
- Mexico (1)
- Micro-XRF (1)
- Micro-fades (1)
- Microhabitats (1)
- Middle-Upper Permian (1)
- Milankovitch (1)
- Mineral composition (1)
- Mineralogy (1)
- Model comparison (1)
- Model selection (1)
- Modeling (1)
- Modern analogue technique (1)
- Molasse Basin (1)
- Mondsee (1)
- Mongolia (1)
- Monitoring (1)
- Moulouya river basin (1)
- Mozambique Ocean (1)
- Multi-proxy record (1)
- Multi-site study (1)
- Multi-temporal (1)
- Multicomponent ground-penetrating radar (GPR) data (1)
- Multivariate adaptive regression splines (1)
- Multivariate regression trees (1)
- N (1)
- NDVI temporal profiles (1)
- NW Himalaya (1)
- Najd aquifer (1)
- Near East (1)
- Neo-Tethys (1)
- Neotectonics (1)
- Net precipitation (1)
- Neural networks (1)
- Neutron radiography (1)
- Non-marine (1)
- North Africa (1)
- North Atlantic (1)
- North-eastern Germany (1)
- Northern Hemisphere Glaciation (1)
- Nutrients (1)
- O ligands (1)
- Ocean acidification (1)
- Oligochaeta (1)
- Oman (1)
- Open source (1)
- Open tropical rain forest (1)
- Organic matter (1)
- Overland flow (1)
- Oxygen mapping (1)
- PETM (1)
- Palaeo-lake sediments (1)
- Palaeo-landslides (1)
- Palaeo-shorelines (1)
- Palaeoclimate (1)
- Paleo-ecology (1)
- Paleo-tethys (1)
- Paleoclimate (1)
- Paleofloods (1)
- Paleohydrology (1)
- Paläohochwasser (1)
- Pan-African magmatism (1)
- Panama Canal watershed (1)
- Pedotransfer function (1)
- Permian-Triassic boundary (1)
- Perumytilus mussels (1)
- Phenological correction (1)
- Pine (1)
- Plio-Pleistocene (1)
- Plio-Pleistocene transition (1)
- Polarimetrie (1)
- Polarimetry (1)
- Population dynamics (1)
- Poshtuk metapelites (1)
- Precipitation pattern (1)
- Precipitation reconstruction (1)
- Principal component analysis (1)
- Probabilistic forecasting (1)
- Procrustes analysis (1)
- Protolith (1)
- Quantile Regression Forest model (1)
- Quantile regression forests (1)
- Quaternary (1)
- RETC (1)
- Rainforest (1)
- Recharge (1)
- Redundancy analysis (1)
- Reference site (1)
- Regional scale (1)
- Regularisierung (1)
- Rhizosphere (1)
- River Isabena (1)
- River profiles (1)
- Root respiration (1)
- S-type granite (1)
- SAR (1)
- SDM (1)
- SEBAL (1)
- SW Africa (1)
- Salinity (1)
- Sediment geochemistry (1)
- Sediment storage (1)
- Sediment transport (1)
- Sediment yield (1)
- Sedimentology (1)
- Seesediment (1)
- Seesedimente (1)
- Seismic gap (1)
- Seismic hazard assessment (1)
- Seismic monitoring and test-ban treaty verification (1)
- Seismic noise (1)
- Seismo-volcanic activity (1)
- Seismologie (1)
- Sensitive areas (1)
- Shallow-water carbonates (1)
- Signal enhancement (1)
- Site effects (1)
- Slip deficit (1)
- Slip distribution (1)
- Soil development (1)
- Soil moisture (1)
- Soil moisture measurement comparison (1)
- Soil moisture regimes (1)
- Soil reaction (1)
- Soil thin-section (1)
- Solute evolution (1)
- Southern Italy (1)
- Soybean (1)
- Spatial analysis and modelling tool (SAMT) (1)
- Spectral decomposition (1)
- Spectral intensity (1)
- Spiti valley (1)
- Spity Valley (1)
- Statistical modeling (1)
- Steilwinkel-Analyse von PcP (1)
- Structure effect (1)
- Subaerial exposure (1)
- Subduction zone processes (1)
- Subsurface biosphere (1)
- Subterranean environment (1)
- Surface roughness (1)
- Suspended-sediment yield (1)
- Swarm earthquakes (1)
- Tectonic deformation (1)
- Tectonic geomorphology (1)
- Temperature reconstruction (1)
- Tetrahymanol (1)
- Thaw lakes (1)
- The Netherlands (1)
- Thermochronology (1)
- Thermokarst (1)
- Tiefbeben und Kernexplosionen (1)
- Time-series analysis (1)
- Tomography (1)
- Total organic carbon (1)
- Transferverluste in Flüssen (1)
- Transform faults (1)
- Tree age distribution (1)
- Tree-based pursuit (1)
- Triassic (1)
- Trockenflüsse (1)
- Tropical forest (1)
- Tropical montane forests (1)
- Trout Lake (1)
- Tsunamis (1)
- Turkey (1)
- UHP metamorphism (1)
- Ultra-Niedriggeschwindigkeitszonen (1)
- Uncertainty (1)
- Uncertainty Analysis (1)
- Unsicherheitsanalyse (1)
- Varve chronology (1)
- Vegetation (1)
- Vermicompost (1)
- Volcano monitoring (1)
- Volcano seismology (1)
- WAPLS (1)
- WaSiM-ETH (1)
- Warven (1)
- Warves (1)
- Water balance model (1)
- Water chemistry (1)
- Water distribution (1)
- Water resources (1)
- Weighted model ensembles (1)
- West Bohemia (1)
- Westerlies (1)
- Wind model (1)
- Wind tunnel experiments (1)
- Woodchips (1)
- XRF (1)
- Zechstein-Buntsandstein interval (1)
- Zircon U/Pb and Pb-Pb ages (1)
- Zooxanthellate corals (1)
- accretionary prism (1)
- adsorption (1)
- aeolian input (1)
- age resetting (1)
- ambient noise (1)
- anisotropic inversion (1)
- basal accretion (1)
- biodiversity (1)
- biomarkers (1)
- biostratigraphy (1)
- carbon dioxide (1)
- carbonate ramp (1)
- cell enumeration (1)
- channel projection (1)
- climate dynamics (1)
- climate-tectonic feedback processes (1)
- conductivity anisotropy (1)
- core-mantle boundary (1)
- cosmogenic nuclides (1)
- cosmogenic radionuclides (1)
- crust (1)
- cyclic stratigraphy (1)
- debris-flow topography (1)
- deep biosphere (1)
- deep earthquakes and nuclear explosions (1)
- deep-marine sedimentary processes (1)
- deuterium (1)
- developing countries (1)
- diatom-bound nitrogen isotopes (1)
- discontinuity surfaces (1)
- dispersion maxima (1)
- dust (1)
- dust emission and deposition (1)
- ecological forecasts (1)
- ecological niche modelling (1)
- ecological theory (1)
- effectiveness (1)
- fluvial strath terraces (1)
- food quality (1)
- foreland basin (1)
- frontal accretion (1)
- fuzzy logic (1)
- gas partial pressure (1)
- geodynamic evolution of SE Anatolia (1)
- geographical range shifts (1)
- glaciers (1)
- global environmental change (1)
- global microbial biomass (1)
- grain boundary sliding (1)
- grazing (1)
- groundwater table (1)
- habitat suitability models (1)
- hardgrounds (1)
- heat flow (1)
- high-pressure incubation system (1)
- hotspot (1)
- hydrodynamic level (1)
- hydrologische Modellierung (1)
- hydrous melt (1)
- impact assessment (1)
- integrative modelling framework (1)
- lake sediments (1)
- lakes (1)
- land use (1)
- landscape evolution (1)
- landslide (1)
- landslides (1)
- light (1)
- lithofacies proportion modeling (1)
- low molecular weight organic acids (1)
- magnetostratigraphy (1)
- magnetotelluric (1)
- magnitude & frequency (1)
- mantle transition zone (1)
- mechanistic model (1)
- mechanistic models (1)
- metal- organic frameworks (1)
- microbial activity (1)
- microporous materials (1)
- migration (1)
- monsoon river hydrology (1)
- multi-attribute (1)
- multi-scale (MA-MS) proportion calibration (1)
- municipality (1)
- n-alkanes (1)
- nachhaltige Entwicklung (1)
- nature conservation (1)
- northwestern Iran (1)
- nutrient status (1)
- oceans (1)
- olivine (1)
- organic geochemistry (1)
- orogenic peridotite (1)
- overwintering (1)
- palaeoecology (1)
- paleoclimate proxy (1)
- paleofloods (1)
- parameterization (1)
- parametric and nonparametric comparison (1)
- parasitism (1)
- pelagic zone (1)
- peperite (1)
- periglacial landscapes (1)
- periglaziale Landschaften (1)
- permafrost (1)
- phase symmetry (1)
- pipe detection (1)
- plume (1)
- pockmark (1)
- polarimetric decompositions (1)
- polarimetrische Dekompositionen (1)
- polarization analysis (1)
- population growth (1)
- principal component analysis (PCA) (1)
- process-based model (1)
- process-based statistics (1)
- pull-apart basin (1)
- quantitative research (1)
- receiver function (1)
- regional development (1)
- regularization (1)
- relative sea-level (1)
- räumliche Analyse (1)
- satellite data (1)
- sea floor morphology (1)
- sea surface temperature reconstructions (1)
- seasonal patterns (1)
- sediment flux hysteresis (1)
- seismology (1)
- semiarid grassland (1)
- shear localization (1)
- sill (1)
- slip model (1)
- soil aggregates (1)
- soil-adjusted vegetation index (1)
- spatial analyses (1)
- spatially and temporally explicit modelling macroecology (1)
- species distribution model (1)
- specific stream power (1)
- steep-angle analysis of PcP (1)
- stochastic dynamical systems (1)
- streamflow probabilistic forecasting (1)
- sub-sampling (1)
- subalkaline to alkaline magmatism (1)
- subarctic Pacific stratification (1)
- subduction (1)
- subduction history (1)
- subsurface life (1)
- sulfate reduction (1)
- superplasticity (1)
- suspended sediment transport (1)
- sustainable development (1)
- tectonophysics (1)
- terrestrial higher plant waxes (1)
- thermal overprint (1)
- thermobarometry (1)
- thermomechanical modeling (1)
- time series analysis (1)
- tomography (1)
- transform fault (1)
- turbidites (1)
- ultra-low velocity zones (1)
- ultrasonication (1)
- uncertainty (1)
- uplift (1)
- upper mantle (1)
- validation (1)
- van Genuchten-Mualem (1)
- varves (1)
- water availability (1)
- water management (1)
- water scarcity (1)
- water-extractable elements (1)
- wind erosion (1)
- wireline logs (1)
- zinc (1)
- zircon fission-track dating (1)
Institute
- Institut für Geowissenschaften (169) (remove)
The Garzn Complex of the Garzn Massif in SW Colombia is composed of the Vergel Granulite Unit (VG) and the Las Margaritas Migmatite Unit (LMM). Previous studies reveal peak temperature conditions for the VG of about 740 A degrees C. The present study considers the remarkable exsolution phenomena in feldspars and pyroxenes and titanium-in-quartz thermometry. Recalculated ternary feldspar compositions indicate temperatures around 900-1,000 A degrees C just at or above the ultra-high temperature-metamorphism (UHTM) boundary of granulites. The calculated temperatures range of exsolved ortho- and clinopyroxenes also supports the existence of an UHTM event. In addition, titanium-in-quartz thermometry points towards ultra-high temperatures. It is the first known UHTM crustal segment in the northern part of South America. Although a mean geothermal gradient of ca 38 A degrees C km(-1) could imply additional heat supply in the lower crust controlling this extreme of peak metamorphism, an alternative model is suggested. The formation of the Vergel Granulite Unit is supposed to be formed in a continental back-arc environment with a thinned and weakened crust behind a magmatic arc (Guapotn-Mancagua Gneiss) followed by collision. In contrast, rocks of the adjacent Las Margaritas Migmatite Unit display "normal" granulite facies temperatures and are formed in a colder lower crust outside the arc, preserved by the Guapotn-Mancagu Gneiss. Back-arc formation was followed by inversion and thickening of the basin. The three units that form the modern-day Garzn Massif, were juxtaposed upon each other during collision (at ca. 1,000 Ma) and exhumation. The collision leading to the deformation of the studied area is part of the Grenville orogeny leading to the amalgamation of Rodinia.
The actual evapotranspiration is an important, but difficult to determine, element in the water balance of lakes and their catchment areas. Reliable data on evapotranspiration are not available for most lake basins for which paleoclimate reconstructions and modeling have been performed, particularly those in remote parts of Africa. We have used thermal infrared multispectral data for 14 ASTER scenes from the TERRA satellite to estimate the actual evapotranspiration in the 12,800 km(2) catchment of the Suguta Valley, northern Kenya Rift Evidence from sediments and paleo-shorelines indicates that, during the African Humid Period (AHP, 14.8 to 5.5 kyrs BP), this valley contained a large lake, 280 m deep and covering similar to 2200 km(2), which has now virtually disappeared. Evapotranspiration estimates for the Suguta Basin were generated using the Surface Energy Balance Algorithm for Land (SEBAL). Climate data required for the model were extracted from a high-resolution gridded dataset obtained from the Climatic Research Unit (East Anglia, UK). Results suggest significant spatial variations in evapotranspiration within the catchment area (ranging from 450 mm/yr in the basin to the north to 2000 mm/yr in more elevated areas) and precipitation that was similar to 20% higher during the AHP than in recent times. These results are in agreement with other estimates of paleo-precipitation in East Africa. The extreme response of the lake system (similar to 280 m greater water depth than today, and a lake surface area of 2200 km(2)) to only moderately higher precipitation illustrates the possible sensitivity of this area to future climate change.
A temporary seismic network composed of 11 stations was installed in the city of Potenza (Southern Italy) to record local and regional seismicity within the context of a national project funded by the Italian Department of Civil Protection (DPC). Some stations were moved after a certain time in order to increase the number of measurement points, leading to a total of 14 sites within the city by the end of the experiment. Recordings from 26 local earthquakes (M-l 2.2-3.8 ) were analyzed to compute the site responses at the 14 sites by applying both reference and non-reference site techniques. Furthermore, the Spectral Intensity (SI) for each local earthquake, as well as their ratios with respect to the values obtained at a reference site, were also calculated. In addition, a field survey of 233 single station noise measurements within the city was carried out to increase the information available at localities different from the 14 monitoring sites. By using the results of the correlation analysis between the horizontal-to-vertical spectral ratios computed from noise recordings (NHV) at the 14 selected sites and those derived by the single station noise measurements within the town as a proxy, the spectral intensity correction factors for site amplification obtained from earthquake analysis were extended to the entire city area. This procedure allowed us to provide a microzonation map of the urban area that can be directly used when calculating risk scenarios for civil defence purposes. The amplification factors estimated following this approach show values increasing along the main valley toward east where the detrital and alluvial complexes reach their maximum thickness.
Climate is the principal driving force of hydrological extremes like floods and attributing generating mechanisms is an essential prerequisite for understanding past, present, and future flood variability. Successively enhanced radiative forcing under global warming enhances atmospheric water-holding capacity and is expected to increase the likelihood of strong floods. In addition, natural climate variability affects the frequency and magnitude of these events on annual to millennial time-scales. Particularly in the mid-latitudes of the Northern Hemisphere, correlations between meteorological variables and hydrological indices suggest significant effects of changing climate boundary conditions on floods. To date, however, understanding of flood responses to changing climate boundary conditions is limited due to the scarcity of hydrological data in space and time. Exploring paleoclimate archives like annually laminated (varved) lake sediments allows to fill this gap in knowledge offering precise dated time-series of flood variability for millennia. During river floods, detrital catchment material is eroded and transported in suspension by fluid turbulence into downstream lakes. In the water body the transport capacity of the inflowing turbidity current successively diminishes leading to the deposition of detrital layers on the lake floor. Intercalated into annual laminations these detrital layers can be dated down to seasonal resolution. Microfacies analyses and X-ray fluorescence scanning (µ-XRF) at 200 µm resolution were conducted on the varved Mid- to Late Holocene interval of two sediment profiles from pre-alpine Lake Ammersee (southern Germany) located in a proximal (AS10prox) and distal (AS10dist) position towards the main tributary River Ammer. To shed light on sediment distribution within the lake, particular emphasis was (1) the detection of intercalated detrital layers and their micro-sedimentological features, and (2) intra-basin correlation of these deposits. Detrital layers were dated down to the season by microscopic varve counting and determination of the microstratigraphic position within a varve. The resulting chronology is verified by accelerator mass spectrometry (AMS) 14C dating of 14 terrestrial plant macrofossils. Since ~5500 varve years before present (vyr BP), in total 1573 detrital layers were detected in either one or both of the investigated sediment profiles. Based on their microfacies, geochemistry, and proximal-distal deposition pattern, detrital layers were interpreted as River Ammer flood deposits. Calibration of the flood layer record using instrumental daily River Ammer runoff data from AD 1926 to 1999 proves the flood layer succession to represent a significant time-series of major River Ammer floods in spring and summer, the flood season in the Ammersee region. Flood layer frequency trends are in agreement with decadal variations of the East Atlantic-Western Russia (EA-WR) atmospheric pattern back to 200 yr BP (end of the used atmospheric data) and solar activity back to 5500 vyr BP. Enhanced flood frequency corresponds to the negative EA-WR phase and reduced solar activity. These common links point to a central role of varying large-scale atmospheric circulation over Europe for flood frequency in the Ammersee region and suggest that these atmospheric variations, in turn, are likely modified by solar variability during the past 5500 years. Furthermore, the flood layer record indicates three shifts in mean layer thickness and frequency of different manifestation in both sediment profiles at ~5500, ~2800, and ~500 vyr BP. Combining information from both sediment profiles enabled to interpret these shifts in terms of stepwise increases in mean flood intensity. Likely triggers of these shifts are gradual reduction of Northern Hemisphere orbital summer forcing and long-term solar activity minima. Hypothesized atmospheric response to this forcing is hemispheric cooling that enhances equator-to-pole temperature gradients and potential energy in the troposphere. This energy is transferred into stronger westerly cyclones, more extreme precipitation, and intensified floods at Lake Ammersee. Interpretation of flood layer frequency and thickness data in combination with reanalysis models and time-series analysis allowed to reconstruct the flood history and to decipher flood triggering climate mechanisms in the Ammersee region throughout the past 5500 years. Flood frequency and intensity are not stationary, but influenced by multi-causal climate forcing of large-scale atmospheric modes on time-scales from years to millennia. These results challenge future projections that propose an increase in floods when Earth warms based only on the assumption of an enhanced hydrological cycle.
The potential increase in frequency and magnitude of extreme floods is currently discussed in terms of global warming and the intensification of the hydrological cycle. The profound knowledge of past natural variability of floods is of utmost importance in order to assess flood risk for the future. Since instrumental flood series cover only the last ~150 years, other approaches to reconstruct historical and pre-historical flood events are needed. Annually laminated (varved) lake sediments are meaningful natural geoarchives because they provide continuous records of environmental changes > 10000 years down to a seasonal resolution. Since lake basins additionally act as natural sediment traps, the riverine sediment supply, which is preserved as detrital event layers in the lake sediments, can be used as a proxy for extreme discharge events. Within my thesis I examined a ~ 8.50 m long sedimentary record from the pre-Alpine Lake Mondsee (Northeast European Alps), which covered the last 7000 years. This sediment record consists of calcite varves and intercalated detrital layers, which range in thickness from 0.05 to 32 mm. Detrital layer deposition was analysed by a combined method of microfacies analysis via thin sections, Scanning Electron Microscopy (SEM), μX-ray fluorescence (μXRF) scanning and magnetic susceptibility. This approach allows characterizing individual detrital event layers and assigning a corresponding input mechanism and catchment. Based on varve counting and controlled by 14C age dates, the main goals of this thesis are (i) to identify seasonal runoff processes, which lead to significant sediment supply from the catchment into the lake basin and (ii) to investigate flood frequency under changing climate boundary conditions. This thesis follows a line of different time slices, presenting an integrative approach linking instrumental and historical flood data from Lake Mondsee in order to evaluate the flood record inferred from Lake Mondsee sediments. The investigation of eleven short cores covering the last 100 years reveals the abundance of 12 detrital layers. Therein, two types of detrital layers are distinguished by grain size, geochemical composition and distribution pattern within the lake basin. Detrital layers, which are enriched in siliciclastic and dolomitic material, reveal sediment supply from the Flysch sediments and Northern Calcareous Alps into the lake basin. These layers are thicker in the northern lake basin (0.1-3.9 mm) and thinner in the southern lake basin (0.05-1.6 mm). Detrital layers, which are enriched in dolomitic components forming graded detrital layers (turbidites), indicate the provenance from the Northern Calcareous Alps. These layers are generally thicker (0.65-32 mm) and are solely recorded within the southern lake basin. In comparison with instrumental data, thicker graded layers result from local debris flow events in summer, whereas thin layers are deposited during regional flood events in spring/summer. Extreme summer floods as reported from flood layer deposition are principally caused by cyclonic activity from the Mediterranean Sea, e.g. July 1954, July 1997 and August 2002. During the last two millennia, Lake Mondsee sediments reveal two significant flood intervals with decadal-scale flood episodes, during the Dark Ages Cold Period (DACP) and the transition from the Medieval Climate Anomaly (MCA) into the Little Ice Age (LIA) suggesting a linkage of transition to climate cooling and summer flood recurrences in the Northeastern Alps. In contrast, intermediate or decreased flood episodes appeared during the MWP and the LIA. This indicates a non-straightforward relationship between temperature and flood recurrence, suggesting higher cyclonic activity during climate transition in the Northeast Alps. The 7000-year flood chronology reveals 47 debris flows and 269 floods, with increased flood activity shifting around 3500 and 1500 varve yr BP (varve yr BP = varve years before present, before present = AD 1950). This significant increase in flood activity shows a coincidence with millennial-scale climate cooling that is reported from main Alpine glacier advances and lower tree lines in the European Alps since about 3300 cal. yr BP (calibrated years before present). Despite relatively low flood occurrence prior to 1500 varve yr BP, floods at Lake Mondsee could have also influenced human life in early Neolithic lake dwellings (5750-4750 cal. yr BP). While the first lake dwellings were constructed on wetlands, the later lake dwellings were built on piles in the water suggesting an early flood risk adaptation of humans and/or a general change of the Late Neolithic Culture of lake-dwellers because of socio-economic reasons. However, a direct relationship between the final abandonment of the lake dwellings and higher flood frequencies is not evidenced.
Assuming that liquid iron alloy from the outer core interacts with the solid silicate-rich lower mantle the influence on the core-mantle reflected phase PcP is studied. If the core-mantle boundary is not a sharp discontinuity, this becomes apparent in the waveform and amplitude of PcP. Iron-silicate mixing would lead to regions of partial melting with higher density which in turn reduces the velocity of seismic waves. On the basis of the calculation and interpretation of short-period synthetic seismograms, using the reflectivity and Gauss Beam method, a model space is evaluated for these ultra-low velocity zones (ULVZs). The aim of this thesis is to analyse the behaviour of PcP between 10° and 40° source distance for such models using different velocity and density configurations. Furthermore, the resolution limits of seismic data are discussed. The influence of the assumed layer thickness, dominant source frequency and ULVZ topography are analysed. The Gräfenberg and NORSAR arrays are then used to investigate PcP from deep earthquakes and nuclear explosions. The seismic resolution of an ULVZ is limited both for velocity and density contrasts and layer thicknesses. Even a very thin global core-mantle transition zone (CMTZ), rather than a discrete boundary and also with strong impedance contrasts, seems possible: If no precursor is observable but the PcP_model /PcP_smooth amplitude reduction amounts to more than 10%, a very thin ULVZ of 5 km with a first-order discontinuity may exist. Otherwise, if amplitude reductions of less than 10% are obtained, this could indicate either a moderate, thin ULVZ or a gradient mantle-side CMTZ. Synthetic computations reveal notable amplitude variations as function of the distance and the impedance contrasts. Thereby a primary density effect in the very steep-angle range and a pronounced velocity dependency in the wide-angle region can be predicted. In view of the modelled findings, there is evidence for a 10 to 13.5 km thick ULVZ 600 km south-eastern of Moscow with a NW-SE extension of about 450 km. Here a single specific assumption about the velocity and density anomaly is not possible. This is in agreement with the synthetic results in which several models create similar amplitude-waveform characteristics. For example, a ULVZ model with contrasts of -5% VP , -15% VS and +5% density explain the measured PcP amplitudes. Moreover, below SW Finland and NNW of the Caspian Sea a CMB topography can be assumed. The amplitude measurements indicate a wavelength of 200 km and a height of 1 km topography, previously also shown in the study by Kampfmann and Müller (1989). Better constraints might be provided by a joined analysis of seismological data, mineralogical experiments and geodynamic modelling.
Ostracods from water bodies in hyperarid Israel and Jordan as habitat and water chemistry indicators
(2012)
The hyperarid region of Israel and Jordan covers a large area where numerous sites of Pleistocene lake sediments suggest that climate conditions were significantly wetter during the Pleistocene. This region experienced a significant increase in aridity in recent decades and the number of existing surface waters is diminishing rapidly. We studied ostracod shells from 49 pond and stream sites to determine the species distribution and to infer ecological preferences especially with respect to general differences in water movement, conductivity and ion composition. Twenty-two ostracod species were identified in total of which 12 taxa occur at three or more sites. Among the rarer species. Cyprinotus scholiosus was identified for the first time after two records from Plio- and Pleistocene sites in Yemen and Saudi Arabia. Further, Paracypretta amati was recorded and its ecological preferences discussed for the first time following the description of the species from its type locality in Sudan. Cypridopsis elongata is the only typical inhabitant of lotic habitats, strictly preferring freshwater conditions and waters with an alkalinity/Ca ratio around 1 and cations dominated by Ca(2+) and anions by HCO(3)(-). In contrast, Cyprideis torosa, Limnocythere inopinata and Heterocypris incongruens apparently prefer waters dominated by Na(+) associated with cations and Cl(-) associated with anions. Heterocypris salina and C. torosa occur over a wide conductivity (or salinity) range and in waters with alkalinity/Ca ratios around 1 and with significant alkalinity depletion. Humphcypris subterranea, Ilyocypris spp. and H. sauna are the only taxa which do not show any preference with respect to both the cation and anion dominance of the waters. The ecological preferences of the ostracod species from water bodies in the study area are discussed in detail and can be used for a qualitative assessment of the hydrodynamical and hydrochemical conditions of former water bodies in the presently hyperarid environment based on ostracod species composition analysis of Pleistocene aquatic sediments.
Ostracodes (Ostracoda, Crustacea) are aquatic micro-crustaceans with a significant representation in the fossil record. If the environmental influence on the species composition of their communities is robustly quantified, past changes in ostracode communities reflected in fossil assemblages can be used for paleo-environmental reconstruction. We analyzed ostracode assemblages in recently deposited surface sediments from 56 lakes in western and central Mongolia, and simultaneously recorded local water chemistry and solute concentration in order to elucidate the distribution of individual ostracode species in relation to these broad environmental gradients. Multivariate analysis indicated that the species variation in ostracode assemblages could be mainly attributed to variations in percent calcium (%Ca) relative to total cation content, mean annual precipitation, calcium concentration, alkalinity, percent bicarbonate relative to total anion content, and mean July temperature. This matches well with the results of a similar analysis on presence/absence data of living ostracodes in nearshore samples, even though some differences exist between the faunal composition of both datasets. The documented response of ostracode species to environmental variation tracks the typical solute evolutionary pathway for surface waters in this region, characterized by calcite precipitation and consequent depletion in dissolved calcium. Hence, the best quantitative inference model (WA-PLS model with R-jack(2) = 0.70, RMSEP = 0.40) for paleolimnological application was obtained for %Ca. Comparison between this model and a specific conductance (SC) inference model based on the same dataset, and based on ostracode datasets from different regions, indicated that the %Ca inference model suffers less than the SC inference model from a step-change in reconstructed values. The statistical power of different inference models based on Mongolian ostracodes are variously affected by the common dominance of a single euryhaline species (Limnocythere inopinata), limited faunal turnover in the freshwater portion of the salinity gradient, and the bimodal frequency distribution of SC among regional lakes. The latter probably represents true scarcity of lakes with intermediate salinity rather than a biased representation in our dataset. In a broader context of ostracode ecology, and with respect to regional paleolimnological applications, we highlight the potential of fossil Mongolian ostracode assemblages to trace past hydrological shifts associated with changes in groundwater inflow.
We investigate the crust, upper mantle and mantle transition zone of the Cape Verde hotspot by using seismic P and S receiver functions from several tens of local seismograph stations. We find a strong discontinuity at a depth of similar to 10 km underlain by a similar to 15-km thick layer with a high (similar to 1.9) Vp/Vs velocity ratio. We interpret this discontinuity and the underlying layer as the fossil Moho, inherited from the pre-hotspot era, and the plume-related magmatic underplate. Our uppermost-mantle models are very different from those previously obtained for this region: our S velocity is much lower and there are no indications of low densities. Contrary to previously published arguments for the standard transition zone thickness our data indicate that this thickness under the Cape Verde islands is up to similar to 30 km less than in the ambient mantle. This reduction is a combined effect of a depression of the 410-km discontinuity and an uplift of the 660-km discontinuity. The uplift is in contrast to laboratory data and some seismic data on a negligible dependence of depth of the 660-km discontinuity on temperature in hotspots. A large negative pressure-temperature slope which is suggested by our data implies that the 660-km discontinuity may resist passage of the plume.
Our data reveal beneath the islands a reduction of S velocity of a few percent between 470-km and 510-km depths. The low velocity layer in the upper transition zone under the Cape Verde archipelago is very similar to that previously found under the Azores and a few other hotspots. In the literature there are reports on a regional 520-km discontinuity, the impedance of which is too large to be explained by the known phase transitions. Our observations suggest that the 520-km discontinuity may present the base of the low-velocity layer in the transition zone.
Hydrogen isotope values (delta D) of sedimentary aquatic and terrestrial lipid biomarkers, originating from algae, bacteria, and leaf wax, have been used to record isotopic properties of ancient source water (i.e., precipitation and/or lake water) in several mid-and high-latitude lacustrine environments. In the tropics, however, where both processes associated with isotope fractionation in the hydrologic system and vegetation strongly differ from those at higher latitudes, calibration studies for this proxy are not yet available. To close this gap of knowledge, we sampled surface sediments from 11 lakes in Cameroon to identify those hydro-climatological processes and physiological factors that determine the hydrogen isotopic composition of aquatic and terrestrial lipid biomarkers. Here we present a robust framework for the application of compound-specific hydrogen isotopes in tropical Africa. Our results show that the delta D values of the aquatic lipid biomarker n-C(17) alkane were not correlated with the delta D values of lake water. Carbon isotope measurements indicate that the n-C(17) alkane was derived from multiple source organisms that used different hydrogen pools for biosynthesis. We demonstrate that the delta D values of the n-C(29) alkane were correlated with the delta D values of surface water (i.e., river water and groundwater), which, on large spatial scales, reflect the isotopic composition of mean annual precipitation. Such a relationship has been observed at higher latitudes, supporting the robustness of the leaf-wax lipid delta D proxy on a hemispheric spatial scale. In contrast, the delta D values of the n-C(31) alkane did not show such a relationship but instead were correlated with the evaporative lake water delta D values. This result suggests distinct water sources for both leaf-wax lipids, most likely originating from two different groups of plants. These new findings have important implications for the interpretation of long-chain n-alkane delta D records from ancient lake sediments. In particular, a robust interpretation of palaeohydrological data requires knowledge of the vegetation in the catchment area as different plants may utilise different water sources. Our results also suggest that the combination of carbon and hydrogen isotopes does help to differentiate between the metabolic pathway and/or growth form of organisms and therefore, the source of hydrogen used during lipid biosynthesis.
In Central and NW Europe, the transition from the Permian to the Triassic (i.e., the Zechstein-Buntsandstein boundary interval) is developed mainly in red bed facies. This continental sedimentary succession is marked by relatively high sedimentation rates providing a high temporal resolution favorable for magnetic polarity stratigraphy. Here, we present a Zechstein to Lower Buntsandstein magnetostratigraphy obtained from the c. 100 m thick Everdingen-1 core from the Netherlands. Seven magnetozones (EV1n to EV4n) and five submagnetozones (EV1n.1r to EV3r.1n) have been delineated. The Everdingen-1 magnetostratigraphy has been integrated into the well-established high-resolution Zechstein-Buntsandstein stratigraphic framework, and verifies the geomagnetic polarity record from Central Germany. This confirms the hypothesis of nearly synchronous base-level cycles within the interior of the Central European Basin. These cycles are related to solar-induced similar to 100 ka eccentricity cycles. The most distinctive feature of the Everdingen-1 magnetostratigraphy is a transition from a thin reverse to a thick dominantly normal magnetic polarity interval. This reversal predates both the terrestrial mass extinction, which is indicated by a palynofloral turnover and a major sediment provenance change at the base of the Buntsandstein, and the marine Permian-Triassic Boundary (PTB). The PTB is located within the lowermost Buntsandstein and is approximated by the last occurrence of the conchostracan Falsisca postera and a negative excursion in the carbon isotope record. According to the Buntsandstein cyclostratigraphy, the R/N reversal predates the marine end-Permian extinction event by about 0.1 Ma and the marine biostratigraphic PTB by about 0.2 Ma. The thick normal magnetozone is estimated to have lasted c. 700 ka, and roughly coincides with the main phase of Siberian Trap volcanism.
Disproportionate single-species contribution to canopy-soil nutrient flux in an Amazonian rainforest
(2012)
Rainfall, throughfall and stemflow were monitored on an event basis in an undisturbed open tropical rainforest with a large number of palm trees located in the southwestern Amazon basin of Brazil. Stemflow samples were collected from 24 trees with a diameter at breast height (DBH) > 5 cm, as well as eight young and four full-grown babassu palms (Attalea speciosa Mart.) for 5 weeks during the peak of the wet season. We calculated rainfall, throughfall and stemflow concentrations and fluxes of Na+, K+, Ca2+, Mg2+,, Cl-, SO42-, NO3- and H+ and stemflow volume-weighted mean concentrations and fluxes for three size classes of broadleaf trees and three size classes of palms. The concentrations of most solutes were higher in stemflow than in rainfall and increased with increasing tree and palm size. Concentration enrichments from rainfall to stemflow and throughfall were particularly high (81-fold) for NO3-. Stemflow fluxes of NO3- and H+ exceeded throughfall fluxes but stemflow fluxes of other solutes were less than throughfall fluxes. Stemflow solute fluxes to the forest soil were dominated by fluxes on babassu palms, which represented only 4% of total stem number and 10% of total basal area. For NO3-, stemflow contributed 51% of the total mass of nitrogen delivered to the forest floor (stemflow + throughfall) and represented more than a 2000-fold increase in NO3- flux compared what would have been delivered by rainfall alone on the equivalent area. Because these highly localized fluxes of both water and NO3- persist in time and space, they have the potential to affect patterns of soil moisture, microbial populations and other features of soil biogeochemistry conducive to the creation of hotspots for nitrogen leaching and denitrification, which could amount to an important fraction of total ecosystem fluxes. Because these hotspots occur over very small areas, they have likely gone undetected in previous studies and need to be considered as an important feature of the biogeochemistry of palm-rich tropical forest.
Evaluation of organic matter stability in wood compost by chemical and thermogravimetric analysis
(2012)
This study investigated maturation and stability levels during composting of Quercus robur (QR) woodchips mixed with different nitrogen sources (horse manure, HM and lake mud, LM) for potential agronomic utilisation. The woodchips were mixed with HM and LM, respectively, at mixing ratios of 1QR:2HM or QR:2LM. The experiment was conducted in a greenhouse over 100 days. During composting, organic carbon and its fractioning and humification constituents were quantified. In the final compost product, pH, organic matter (OM), cation exchange capacity (CEC) and selected available nutrients were measured. Thermostability of compost, compared with that of soil and compost mixed with charcoal were also quantified. Results showed OM evolution during the composting process with total organic and extractable carbons and humification indices decreasing, while the degree of humification increased. Compost produced from the 1QR:2HM mix resulted in the highest available nutrients, CEC and OM content values in the final product. Thermogravimetric profiles indicated that compost OM thermostability was higher than that in soil and higher for the 1QR:2HM than the 1QR:2LM mix. Application of charcoal revealed no additional stabilising effect of OM in wood compost.