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61.
Jakobshavns Isbræ in West Greenland (terminus at ≈69° 10′ N/50° W), a major outlet glacier of the Greenland Ice Sheet and a continuously fast-moving ice stream, has long been the fastest moving and one of the most productive glaciers on Earth. It had been moving continuously at speeds of over 20 m/day with a stable front position throughout most of the latter half of the twentieth century, except for relatively small seasonal changes. In 2002, the ice stream apparently suddenly entered a phase of rapid retreat. The ice front started to break up, the floating tongue disintegrated, and the production of icebergs increased. In July 2005, we conducted an extensive aerial survey of Jakobshavns Isbræ to measure and document the present state of retreat compared to our previous field observations since 1996. We use an approach that combines structural analysis of deformation features with continuum mechanics to assess the kinematics and dynamics of glaciers, based on aerial imagery, satellite data and GPS measurements. Results from interpretation of ERS-SAR and ASTER data from 1995 to 2005 in combination with aerial imagery from 1996 to 2005 shed light on the question of changes versus stability and their causes in the Jakobshavns Isbræ dynamical system. The recently observed retreat of Jakobshavns Isbræ is attributed to climatic warming, rather than to an inherent change in the glaciodynamic system. Close to the retreating front, deformation structures are characteristic of extension and disintegration. Deformation provinces that do not border the retreating front have had the same deformation characteristics throughout the past decade (1996–2005). 相似文献
62.
Knut Barthel Ute Daewel Dhanya Pushpadas Corinna Schrum Marius ?rthun Henning Wehde 《Ocean Dynamics》2012,62(10-12):1457-1470
This article presents some advantages using a shape-preserving total variation diminishing (TVD) advection scheme in an ecosystem model. The superbee flux-limiter has been used to the second-order Lax–Wendroff advection scheme to make it TVD. We performed simulations for three shelf sea regions with different characteristic time scales, namely, the North Sea, the Barents Sea, and the Baltic Sea. To explore the advantages, we also performed reference runs with the much simpler and computationally cheaper upwind advection scheme. Frontal structures are much better resolved with the TVD scheme. The bottom salinity in the Baltic Sea stays at realistic values throughout the 10-year simulation with the TVD scheme, while with the upwind scheme, it drifts towards lower values and the permanent haline stratification in the Baltic is almost completely eroded within one seasonal cycle. Only when applying TVD for both the vertical and horizontal advections the model succeeded to preserve haline stratification in the decadal simulation. Lower trophic level patterns are far better reproduced with the TVD scheme, and for the estimated cod larval survival, the advantages seem to be even stronger. Simulations using the TVD-derived prey fields identified distinct regions such as Dogger Bank to favor potential larvae survival (PLS), which did not appear as particularly favorable in the upstream simulations. The TVD scheme needs about 25?% more time on the central processing unit (CPU) in case of a pure hydrodynamic setup with only two scalar state variables (Barents Sea application). The additional CPU time cost increases for a coupled physical–biological model application with a large number of state variables. However, this is more than compensated by all the advantages found, and, hence, we conclude that it is worthwhile to use the TVD scheme in our ecosystem model. 相似文献
63.
Ute Weckmann 《Surveys in Geophysics》2012,33(1):107-134
The African continent inherits a long history of continental accretion and breakup. The stage of “making” a continent goes
back to the Archean, when the first continental masses formed cratons which mostly remained stable ever since. Subsequent
collision of weaker continental masses was followed by several extension and compression episodes that resulted in the formation
of super-continents. After the assemblage of Gondwana, a period of predominantly “breaking” , i.e., the breakup of super-continents,
took over. The modern-day African continent exhibits different types of margins; continental rifting occurs side by side with
recent collision. Since the late 1960s, magnetotelluric (MT) experiments have played an important role in studies of the electrical
conductivity structure of Africa. The early results significantly shaped the MT community’s understanding of continental-scale
conductivity belts and basic characteristics of cratons and mobile belts on both crustal and lithospheric mantle scales for
some decades. Modern MT studies in Africa have generally supported earlier results with high resistivities observed on cratons
and low resistivities observed across mobile belts. Advances in instrumentation, data processing and interpretation resulted
in higher-resolution images of the lithosphere, which in consequence induce an improved understanding of tectonic processes
and geological prerequisites for the occurrence of natural resources. The high electrical conductivity of mobile belts and
their relation to reactivated fault and detachment zones were often interpreted to characterize mobile belts as tectonic weak
zones, which can accommodate stress and constitute zones along which continents can break. Recent breaking of the African
continent can be studied on land across the East African rift; however, the lack of amphibian MT experiments across today’s
margins does not allow for good resolution of remnants of continental breakup processes. Naturally, the regions and the focus
of the MT studies in Africa are diverse, but they all contribute to the story of making and breaking a continent. 相似文献
64.
Joerg Ruedrich York Rieffel Stephan Pirskawetz Holger Alpermann Ute Joksch Christoph Gengnagel Frank Weise Rudolph Plagge Jianhua Zhao Siegfried Siegesmund 《Environmental Earth Sciences》2011,63(7-8):1823-1848
The present study documents the results of an inter-disciplinary model project that was planned with the aim of developing an innovative winter covering system for marble statuaries located on the Schlossbrücke (Berlin). Such a system would need to fulfil the various requirements for structural stability, aesthetics, climate and practical use. This applied research represents the first complex scientific study of the sustainability of a winter covering system. The study is characterised by the use of complex scientific instruments such as special laboratory analysis and numerical simulation tools. The interaction between the environment and the artefacts in connection with the innovative winter covering structures were studied by extensive climatic monitoring. 相似文献
65.
Ute Christina Herzfeld 《Mathematical Geology》1996,28(2):137-160
In 1963, Gandin published a monograph on optimum interpolation for the objective analysis of meteorological fields, ≓ a method that is similar mathematically to geodetical least-squares prediction and collocation, simple kriging, and spectral interpolation. The common problem is the interpolation or extrapolation or estimation of a continuous spatial property from finitely many observations. Gandin 's method is presented in an inverse-theoretical context with focus on a methodological comparison with related methods. Underlying mathematical assumptions as well as geological implications are discussed. An introductory overview of inverse methods in the earth sciences is given, with emphasis on methods with a structure analysis step. 相似文献
66.
Catchments as reactors: a comprehensive approach for water fluxes and solute turnover 总被引:1,自引:1,他引:0
Peter Grathwohl Hermann Rügner Thomas Wöhling Karsten Osenbrück Marc Schwientek Sebastian Gayler Ute Wollschläger Benny Selle Marion Pause Jens-Olaf Delfs Matthias Grzeschik Ulrich Weller Martin Ivanov Olaf A. Cirpka Ulrich Maier Bertram Kuch Wolfgang Nowak Volker Wulfmeyer Kirsten Warrach-Sagi Thilo Streck Sabine Attinger Lars Bilke Peter Dietrich Jan H. Fleckenstein Thomas Kalbacher Olaf Kolditz Karsten Rink Luis Samaniego Hans-Jörg Vogel Ulrike Werban Georg Teutsch 《Environmental Earth Sciences》2013,69(2):317-333
Sustainable water quality management requires a profound understanding of water fluxes (precipitation, run-off, recharge, etc.) and solute turnover such as retention, reaction, transformation, etc. at the catchment or landscape scale. The Water and Earth System Science competence cluster (WESS, http://www.wess.info/) aims at a holistic analysis of the water cycle coupled to reactive solute transport, including soil–plant–atmosphere and groundwater–surface water interactions. To facilitate exploring the impact of land-use and climate changes on water cycling and water quality, special emphasis is placed on feedbacks between the atmosphere, the land surface, and the subsurface. A major challenge lies in bridging the scales in monitoring and modeling of surface/subsurface versus atmospheric processes. The field work follows the approach of contrasting catchments, i.e. neighboring watersheds with different land use or similar watersheds with different climate. This paper introduces the featured catchments and explains methodologies of WESS by selected examples. 相似文献
67.
68.
Mathematical Geosciences - 相似文献
69.
Ute Mann Jochen Knies Shyam Chand Wilfried Jokat Ruediger Stein Janine Zweigel 《Marine and Petroleum Geology》2009,26(8):1624-1639
With the recently recovered organic-rich sediments of early Tertiary age from the Lomonosov Ridge by the Integrated Ocean Drilling Program (IODP) Expedition 302, the first data collection directly from source rocks of the central basins of the Arctic Ocean is now available. Using the results of seismic interpretations and published sedimentological and organic geochemical data from Expedition 302, the framework for the first quantitative assessment of source-rock quality and distribution of the Palaeogene sediments was modelled in the central Arctic Ocean. The modelling results suggest that an approximately 100-m-thick Early to Middle Eocene sedimentary sequence of good to very good source rocks exists along a 75 km long transect across the Lomonosov Ridge. In-situ generation of hydrocarbons is unlikely because the overburden (200–250 m) and consequently the thermal maturity are too low. Burial history and thermal modelling reveal that an additional overburden of at least 1000 m is necessary to start hydrocarbon generation along the ridge. However, source-rock modelling results show that good source-rock potential may exist in correlative units in the adjacent Amundsen Basin. Simulated organic carbon contents of 1.5–5%, coupled with an overburden of 1000–1200 m, and heat flow anomalies (117 and 100 mW m−2) due to the vicinity to the Gakkel Ridge spreading centre indicate that necessary conditions for hydrocarbon expulsion are already reached, and point to viability of a potential petroleum system. Our results support the hypothesis that deposition of a potentially good hydrocarbon source rock occurred across the entire Arctic Basin and adjacent margins during the early Tertiary. 相似文献
70.
David Kaeter Martin A. Ziemann Ute Böttger Iris Weber Lutz Hecht Sergey A. Voropaev Alexander V. Korochantsev Andrey V. Kocherov 《Meteoritics & planetary science》2018,53(3):416-432
We present results of petrographic, mineralogical, and chemical investigations of three Chelyabinsk meteorite fragments. Three distinct lithologies were identified: light S3 LL5, dark S4–S5 LL5 material, and opaque fine-grained former impact melt. Olivine–spinel thermometry revealed an equilibration temperature of 703 ± 23 °C for the light lithology. All plagioclase seems to be secondary, showing neither shock-induced fractures nor sulfide-metal veinlets. Feldspathic glass can be observed showing features of extensive melting and, in the dark lithology, as maskelynite, lacking melt features and retaining grain boundaries of former plagioclase. Olivine of the dark lithology shows planar deformation features. Impact melt is dominated by Mg-rich olivine and resembles whole-rock melt. Melt veins (<2 mm) are connected to narrower veinlets. Melt vein textures are similar to pegmatite textures showing chilled margins, a zone of inward-grown elongated crystals and central vugs, suggesting crystallization from supercooled melt. Sulfide-metal droplets indicate liquid immiscibility of both silicate and sulfide as well as sulfide and metal melts. Impact melting may have been an important factor for differentiation of primitive planetary bodies. Graphite associated with micrometer-sized melt inclusions in primary olivine was detected by Raman mapping. Carbon isotopic studies of graphite could be applied to test a possible presolar origin. 相似文献