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  • 1
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 551 ; VAQ 990 ; Meereis {Glaziologie}
    Language: German
    Type: monograph , publishedVersion
    Format: application/pdf
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  • 2
    Publication Date: 2021-03-29
    Description: Sea-ice, Finite Element Sea-Ice Model, Kalman Filter, Data Assimilation. - The Arctic region is sensitive to climate change. Since the Arctic sea-ice cover influences the surface heat budget of the Earth the observed sea-ice decline is seen as an indication of global warming. Furthermore, the dynamics of sea ice plays an important role for the sea-ice mass distribution in the Arctic, for the production of dense, cold, and salty water in the Arctic Ocean, which contributes to the thermohaline circulation, and also for the freshwater budget of the Nordic Seas. Thus, a realistic description of sea-ice motion is important to draw conclusions for the mass transport and sea-ice mass distribution. The Finite-Element Sea-Ice Model simulates the large-scale physical sea-ice processes like the sea-ice growth and circulation realistically. The model domain covers the entire Arctic Ocean and its marginal seas. Together with the Singular Evolutive Interpolated Kalman (SEIK) Filter and remotely sensed sea-ice drift observations this sea-ice model is applied for data assimilation to investigate details of the sea-ice dynamics. So far, drift assimilation has been carried out to analyze and modify only the drift field with subsequent computation of the advection or redistribution of ice mass which corresponds more to the physical model behavior than a statistical analysis that the SEIK Filter provides. The sea-ice drift data assimilation with the SEIK Filter achieves drift modification and furthermore changes in the two other sea-ice variables concentration and thickness. The modifications of these "unobserved variables" (within the meaning of data assimilation) are validated and it is found that they are in good agreement for at least 2 months for the sea-ice thickness and even 4 months for the sea-ice concentration which is the longest period examined. The drift improvement is achieved due to the sea-ice concentration and ...
    Description: thesis
    Keywords: 551 ; 550 ; VAQ 990 ; VAQ 500 ; TVH 100 ; TOY 000 ; Meereis {Glaziologie} ; Gletscherbewegung und Gletscherschwankungen ; Wärme- und Strahlungshaushalt der Atmosphäre {Meteorologie} ; Energiebilanzen in der Geodynamik {Geophysik}
    Language: German
    Type: monograph , publishedVersion
    Format: 141 S.
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  • 3
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    Univ. Bremen
    Publication Date: 2021-03-29
    Description: Ice, microstructures, subgrain boundaries, recrystallization, flow, deformation. - The primary objective of this thesis is the investigation of microstructures obtained from samples from the EPICA Dronning Maud Land ice core from Antarctica. The goal is to gain understanding of deformation processes an deformation-related recrystallization mechanisms using these structures. The structures are visualized with the new microstructure mapping method using the preferred sublimation along defect regions in the crystal. This method enables observation in high resolution as well as overview over a significant sample volume. In order to provide unambiguous proof of their deformational origin and to offer interpretation and characterization, experimental reproduction of the microstructural features are performed using creep tests. Subgrain boundaries and grain-boundary morphology are identified as the most direct effects of deformation and recrystallization processes, which are still easily observable. They can be used additionally to the conventional parameters (grain size, crystal-orientation distribution) to determine these mechanisms. Different sbugrain-boundary types observed in experimentally deformed samples as well as in natural ice indicate several formation processes. Results obtained from this new and novel data suggest a profound reconsideration of the classical tripartition of recrystallization regimes described in the literature in ice sheets. Instead, dynamic recrystallization in two of its forms (rotation recrystallization and strain-induced migration recrystallization) dominates the microstructure evolution in all depth regions of the EDML ice core. Results of systematic microstructure analysis of creep-test samples demonstrate ...
    Description: thesis
    Keywords: 551.312 ; 548.842 ; 551 ; 550 ; VAE 140 ; VAQ 100 ; Gesteinsdeformation {Strukturgeologie} ; Gletscheruntersuchungen im Allgemeinen
    Language: German
    Type: monograph , publishedVersion
    Format: 129 S.
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  • 4
    Publication Date: 2021-03-29
    Description: Sediment transport, high productivity, submarine canyon, submarine slide, excess pore-pressure, weak layers, slope failure. - The study investigates processes of mass sediment transport in two geologically unique Atlantic margins influenced by high primary productivity, i.e. the Mauritanian and Uruguayan margins. Whereas the Mauritanian margin is dominated by hyper-arid conditions, the Uruguayan margin, on the other hand, is dominated by fluvial sediment inputs. Investigations of the Mauritanian margin are centred on two major features, i.e. the Cap Timiris Canyon and the Mauritania Slide Complex, using combined analyses of hydroacoustic and high resolution multi-channel seismic (MCS) data. An area offshore Uruguay, which is dominated by extensive slope instabilities and mass sediment transport, was also investigated with high resolution MCS data. Results of the study suggest ...
    Description: thesis
    Keywords: 551 ; 551 ; 550 ; Atlantischer Ozean {Geophysik} ; Marine Sedimentation {Geologie}
    Language: German
    Type: monograph , publishedVersion
    Format: 130 S.
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