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11.
Yongbo Wang Ulrike Herzschuh Xingqi Liu Oliver Korup Bernhard Diekmann 《Journal of Paleolimnology》2014,51(2):303-312
Lacustrine sediments have been widely used to investigate past climatic and environmental changes on millennial to seasonal time scales. Sedimentary archives of lakes in mountainous regions may also record non-climatic events such as earthquakes. We argue herein that a set of 64 annual laminae couplets reconciles a stratigraphically inconsistent accelerator mass spectrometry (AMS) 14C chronology in a ~4-m-long sediment core from Lake Mengda, in the north-eastern Tibetan Plateau. The laminations suggest the lake was formed by a large landslide, triggered by the 1927 Gulang earthquake (M = 8.0). The lake sediment sequence can be separated into three units based on lithologic, sedimentary, and isotopic characteristics. Starting from the bottom of the sequence, these are: (1) unweathered, coarse, sandy valley-floor deposits or landslide debris that pre-date the lake, (2) landslide-induced, fine-grained soil or reworked landslide debris with a high organic content, and (3) lacustrine sediments with low organic content and laminations. These annual laminations provide a high-resolution record of anthropogenic and environmental changes during the twentieth century, recording enhanced sediment input associated with two phases of construction activities. The high mean sedimentation rates of up to 4.8 mm year?1 underscore the potential for reconstructing such distinct sediment pulses in remote, forested, and seemingly undisturbed mountain catchments. 相似文献
12.
Anne-Cathrin Wölfl Chai Heng Lim H. Christian Hass Sebastian Lindhorst Gabriela Tosonotto Karsten Alexander Lettmann Gerhard Kuhn Jörg-Olaf Wolff Doris Abele 《Geo-Marine Letters》2014,34(5):435-446
Marine habitats worldwide are increasingly pressurized by climate change, especially along the Antarctic Peninsula. Well-studied areas in front of rapidly retreating tidewater glaciers like Potter Cove are representative for similar coastal environments and, therefore, shed light on habitat formation and development on not only a local but also regional scale. The objective of this study was to provide insights into habitat distribution in Potter Cove, King George Island, Antarctica, and to evaluate the associated environmental processes. Furthermore, an assessment concerning the future development of the habitats is provided. To describe the seafloor habitats in Potter Cove, an acoustic seabed discrimination system (RoxAnn) was used in combination with underwater video images and sediment samples. Due to the absence of wave and current measurements in the study area, bed shear stress estimates served to delineate zones prone to sediment erosion. On the basis of the investigations, two habitat classes were identified in Potter Cove, namely soft-sediment and stone habitats that, besides influences from sediment supply and coastal morphology, are controlled by sediment erosion. A future expansion of the stone habitat is predicted if recent environmental change trends continue. Possible implications for the Potter Cove environment, and other coastal ecosystems under similar pressure, include changes in biomass and species composition. 相似文献
13.
Ulrike?WackerEmail author K.?V.?Jayaraman?Potty Christof?Lüpkes J?rg?Hartmann Matthias?Raschendorfer 《Boundary-Layer Meteorology》2005,117(2):301-336
The mesoscale weather prediction model ’Lokal-Modell’ (LM) of the Deutscher Wetterdienst is applied to the situation of an
Arctic cold air outbreak in the Fram Strait region in April 1998. Observations are available from a flight along 50E carried out during the ARTIST campaign. Initial and time-dependent boundary data for the simulation are taken from a larger
scale operational model system.
Using the standard configuration of LM, the simulation reproduced the propagation of cold air and the characteristic structure
of the atmospheric boundary layer (ABL) in fair agreement with the observations. However, a detailed comparison revealed three
basic problems. Firstly, there is evidence that the available data on sea-ice conditions were insufficient approximations
to the true state for several reasons. A modification of the sea-ice data towards observations revealed that parts of the
discrepancies were due to the original sea-ice data. Secondly, a control run with the model in its standard configuration
shows an insufficient warming of the ABL downstream of the ice edge due to underestimation of surface heat fluxes. A simple
modification of the approach for the scalar roughness length resulted in the strongest benefit, while comparative studies
showed only a slight sensitivity to different types of parametrisation of turbulent mixing or the inclusion of an additional
moist convection parametrisation. Thirdly, in all the simulations the deepening of the convective ABL downstream of the ice
edge is weaker than observed. This may be partly due to the thermal stratification above the ABL in the analysis data, which
is more stable than observed; but it may also be a hint to the fact that processes near the inversion are insufficiently parametrised
in mesoscale models with resolutions as used in LM. The simulated cloud layer in the convective ABL is similar to that observed
with respect to condensate content, a sharply defined cloud top, a diffuse lower bound, and continuous light precipitation. 相似文献
14.
Ensemble modelling was used to assess the robustness of projected impacts of pumped‐storage (PS) operation and climate change on reservoir ice cover. To this end, three one‐dimensional and a two‐dimensional laterally averaged hydrodynamic model were set up. For the latter, the strength of the impacts with increasing distance from the dam was also investigated. Climate change effects were simulated by forcing the models with 150 years of synthetic meteorological time series created with a weather generator based on available air temperature scenarios for Switzerland. Future climate by the end of the 21st century was projected to shorten the ice‐covered period by ~2 months and decrease ice thicknesses by ~13 cm. Under current climate conditions, the ice cover would already be affected by extended PS operation. For example, the average probability of ice coverage on a specific day was projected to decrease by ~13% for current climate and could further be reduced from ~45% to ~10% for future climate. Overall, the results of all models were consistent. Although the number of winters without ice cover was projected to increase for all one‐dimensional models, studying individual segments of the two‐dimensional model showed that the impact was pronounced for segments close to the PS intake/outlet. In summary, the reservoir's ice cover is expected to partially vanish with higher probability of open water conditions closer to the PS intake/outlet. 相似文献
15.
Richard?W.?HenleyEmail authorView authors OrcID profile Frank?J.?Brink Penelope?L.?King Clyde?Leys Jibamitra?Ganguly Terrance?Mernagh Jill?Middleton Christian?J.?Renggli Melanie?Sieber Ulrike?Troitzsch Michael?Turner 《Contributions to Mineralogy and Petrology》2017,172(11-12):106
The 2.7–3 Ma Ertsberg East Skarn System (Indonesia), adjacent to the giant Grasberg Porphyry Copper deposit, is part of the world’s largest system of Cu–Au skarn deposits. Published fluid inclusion and stable isotope data show that it formed through the flux of magma-derived fluid through contact metamorphosed carbonate rock sequences at temperatures well above 600° C and pressures of less than 50 MPa. Under these conditions, the fluid has very low density and the properties of a gas. Combining a range of micro-analytical techniques, high-resolution QEMSCAN mineral mapping and computer-assisted X-ray micro-tomography, an array of coupled gas–solid reactions may be identified that controlled reactive mass transfer through the ~ 1 km3 hydrothermal skarn system. Vacancy-driven mineral chemisorption reactions are identified as a new type of reactive transport process for high-temperature skarn alteration. These gas–solid reactions are maintained by the interaction of unsatisfied bonds on mineral surfaces and dipolar gas-phase reactants such as SO2 and HCl that are continuously supplied through open fractures and intergranular diffusion. Principal reactions are (a) incongruent dissolution of almandine-grossular to andradite and anorthite (an alteration mineral not previously recognized at Ertsberg), and (b) sulfation of anorthite to anhydrite. These sulfation reactions also generate reduced sulfur with consequent co-deposition of metal sulfides. Diopside undergoes similar reactions with deposition of Fe-enriched pyroxene in crypto-veins and vein selvedges. The loss of calcium from contact metamorphic garnet to form vein anhydrite necessarily results in Fe-enrichment of wallrock, and does not require Fe-addition from a vein fluid as is commonly assumed. 相似文献
16.
Hartmut H. Hellmer Monika Rhein Günther Heinemann Janna Abalichin Wafa Abouchami Oliver Baars Ulrich Cubasch Klaus Dethloff Lars Ebner Eberhard Fahrbach Martin Frank Gereon Gollan Richard J. Greatbatch Jens Grieger Vladimir M. Gryanik Micha Gryschka Judith Hauck Mario Hoppema Oliver Huhn Torsten Kanzow Boris P. Koch Gert König-Langlo Ulrike Langematz Gregor C. Leckebusch Christof Lüpkes Stephan Paul Annette Rinke Bjoern Rost Michiel Rutgers van der Loeff Michael Schröder Gunther Seckmeyer Torben Stichel Volker Strass Ralph Timmermann Scarlett Trimborn Uwe Ulbrich Celia Venchiarutti Ulrike Wacker Sascha Willmes Dieter Wolf-Gladrow 《Ocean Dynamics》2016,66(11):1379-1413
17.
Nicole Scheifhacken Ulrike Haase Lesya Gram-Radu Roman Kozovyi Thomas U. Berendonk 《Environmental Earth Sciences》2012,65(5):1483-1499
Recently, the Ukrainian Western Bug water authorities developed a national field survey to assess the quality of river habitats.
The Ukrainian government already cooperates with EU member states along transboundary rivers and also orientates itself towards
the European Water Framework Directive (WFD). As a future application for EU membership is feasible, the water authorities
started to implement WFD criteria into their national survey schemes including the assessment of rivers’ hydromorphology.
This article compares two different hydromorphological survey methods to identify similarities and differences of the classification
approaches with regard to the conformity of obtained outputs with the WFD demands. The field surveys, the Ukrainian (UA-FS)
and the German (LAWA-FS), were applied in parallel on 14 river sections along the Western Bug River and parts of its tributaries.
Results show a wide range of conformity, but also several differences between and gaps within all methods. The UA-FS generally
lacks the idea of reference condition in rivers’ hydromorphology and the definition of different stream types or near-natural
land uses. The UA-FS and the LAWA-FS approaches are similar with respect to their incorporated compartments and most main
parameters, but differ in definition and interpretation of specific functional units and single parameters. Greatest similarities
down to single parameters exist in aspects of land use, bank vegetation, currents diversity, and within-stream variation of
water depths. Differences include the assessment and interpretation of lateral erosion, sinuosity, type and depth of profile,
substrate diversity, as well as special structures of bank and riverbed. Overall, the LAWA-FS is more conservative in its
rating than the UA-FS. Still, UA-FS can be regarded as an important improvement for a systematic and reliable monitoring of
river hydromorphology in the Ukraine that will help to successfully engage with both the integrated water resources management
and the WFD harmonisation process in the future. 相似文献
18.
19.
Ulrike Fallet Jenny E. Ullgren Hendrik M. van Aken Herman Ridderinkhof 《Geochimica et cosmochimica acta》2011,75(20):5834-5848
Accurate sea surface temperature (SST) proxies are important for understanding past ocean and climate systems. Here, we examine material collected from a deep-moored sediment trap in the Mozambique Channel (SW Indian Ocean) to constrain and compare both inorganic (δ18O, Mg/Ca) and organic (, TEX86) temperature proxies in a highly dynamic oceanographic setting for application in paleoceanography. High-resolution time-series current velocity data from long-term moorings (2003 - present) deployed across the Mozambique Channel reveal the periodic migration of four to six meso-scale eddies through the channel per year. These meso-scale eddies strongly influence water mass properties including temperature and salinity. Despite the dynamic oceanographic setting, fluxes of the surface-dwelling planktonic foraminifera Globigerinoidesruber and Globigerinoides trilobus follow a seasonal pattern. Temperatures reconstructed from G. ruber and G. trilobus δ18O and Mg/Ca closely mirror seasonal SST variability and their flux-weighted annual mean SSTs of 28.1 °C and 27.3 °C are in close agreement with annual mean satellite SST (27.6 °C). The sub-surface dwelling foraminifera Neogloboquadrina dutertrei and Globigerinoides scitula recorded high-frequency temperature variations that, on average, reflect conditions at water depths of 50-70 m and 200-250 m, respectively. Concentrations and fluxes of organic compounds (alkenones and crenarchaeol) display no or only moderate seasonality but flux weighted means of the associated temperature signatures, , and of 28.3 °C and 28.1 °C, respectively, also closely reflect mean annual SST. We analyzed all time-series data using multiple statistical approaches including cross-correlation and spectral analysis. Eddy variability was clearly expressed in the statistical analysis of physical oceanographic parameters (current velocity and sub-surface temperature) and revealed a frequency of four to six cycles per year. In contrast, statistical analysis of proxy data from the sediment trap did not reveal a significant coupling between eddy migration and organic compound fluxes or reconstructed temperatures. This is likely a result of the relatively low resolution (21 days) and short (2.5 years) duration of the time series, which is close to the detection limit of the eddy frequency. 相似文献
20.
Modest diatom responses to regional warming on the southeast Tibetan Plateau during the last two centuries 总被引:1,自引:0,他引:1
Juliane Wischnewski Anson W. Mackay Peter G. Appleby Steffen Mischke Ulrike Herzschuh 《Journal of Paleolimnology》2011,46(2):215-227
A general mean annual temperature increase accompanied with substantial glacial retreat has been noted on the Tibetan Plateau
during the last two centuries but most significantly since the mid 1950s. These climate trends are particularly apparent on
the southeastern Tibetan Plateau. However, the Tibetan Plateau (due to its heterogeneous mountain landscape) has very complex
and spatially differing temperature and precipitations patterns. As a result, intensive palaeolimnological investigations
are necessary to decipher these climatic patterns and to understand ecological responses to recent environmental change. Here
we present palaeolimnological results from a 210Pb/137Cs-dated sediment core spanning approximately the last 200 years from a remote high-mountain lake (LC6 Lake, working name)
on the southeastern Tibetan Plateau. Sediment profiles of diatoms, organic variables (TOC, C:N) and grain size were investigated.
The 210Pb record suggests a period of rapid sedimentation, which might be linked to major tectonic events in the region ca. 1950.
Furthermore, unusually high 210Pb supply rates over the last 50 years suggest that the lake has possibly been subjected to increasing precipitation rates,
sediment focussing and/or increased spring thaw. The majority of diatom taxa encountered in the core are typical of slightly
acidic to circumneutral, oligotrophic, electrolyte-poor lakes. Diatom species assemblages were rich, and dominated by Cyclotella sp., Achnanthes sp., Aulacoseira sp. and fragilarioid taxa. Diatom compositional change was minimal over the 200-year period (DCCA = 0.85 SD, p = 0.59); only a slightly more diverse but unstable diatom assemblage was recorded during the past 50 years. The results indicate
that large-scale environmental changes recorded in the twentieth century (i.e. increased precipitation and temperatures) are
likely having an affect on the LC6 Lake, but so far these impacts are more apparent on the lake geochemistry than on the diatom
flora. Local and/or regional peculiarities, such as increasing precipitation and cloud cover, or localized climatic phenomena,
such as negative climate feedbacks, might have offset the effects of increasing mean surface temperatures. 相似文献