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  • 11
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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.
    Format: application/pdf
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  • 12
    Publication Date: 2021-03-29
    Description: Vorliegende Arbeit beschäftigt sich mit der Streuung der seismischen Wellen infolge unterschiedlicher, unter Anderen anisotroper, Störungen der sphärischen Symmetrie des Modells. Die Streuwellen übelagern das Referenzsignal und ermöglichen Rückschlüsse auf die verursachende Störung. Die Grundlagen für die störtheoretische Berechnung der synthetischen Seismogramme entstanden noch in den siebziger Jahren des zwanzigsten Jahrhunderts durch Arbeiten von Woodhouse, Dahlen und anderer. Eine effiziente Umsetzung dieser Theorie benötigt aber eine Reihe weiterer Annahmen und Vereinfachungen. Friederich entwickelte eine Methode zum Berechnen der synthetischen Seismogrammen für Erdmodelle mit isotropen elastischen Inhomogenitäten. Seine Methode berücksichtigt mehrfache Streuung in die Richtung der Wellenausbreitung...
    Description: thesis
    Keywords: 551.22 ; 550 ; TOH 100 ; Seismometrie {Geophysik}
    Language: German
    Type: monograph , publishedVersion
    Format: 91 S.
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  • 13
    Publication Date: 2021-03-29
    Description: Antarctica, Dronning Maud Land, anisotropy, seismic anisotropy, shear wave splitting, receiver functions, moho, moho depth, crust, upper mantle, refraction seismic, gravity, 3D-gravity, igmas, bouguer anomaly, seismology. - The area of investigation, Dronning Maud Land (DML), comprises with the Weddell Sea and the Lazarev Sea approximately the region between 15 degrees W and 15 degrees E longitude and 68 degrees and 75 degrees latitude - a surface area of more than 1.500.000 qkm. Three major events formed the present-day geology and tectonic settings of DML: (1) the Grenvillian Orogeny, ca. 1.1 Ga ago, caused by the formation of the supercontinent Rhodinia, (2) the Panafrican Orogeny 500 Ma ago, forming the supercontinent Gondwana due to the collison of West and East Gondwana, and (3) the break-up of Gondwana 180 Ma ago, which started in the present-day Lazarev Sea. Seismological, refraction seismic and aerogravity data-sets form the basis of this thesis. The combination of these data-sets allows to investigate the structural composition and the spatial variation of the lithospheric thickness. The latter is essential for the determination of the regional geoid, which is the main objective of the VISA-project. Within the framework of this project airborne measurements of the potential field as well as ice-penetrating radar and GPS-measurements have been carried out. Moreover, seismographic stations were temporarily deployed in various parts of DML. Despite their very short operation time, applications of seismological methods to the recorded teleseismic events yielded conclusions about the structure and dynamic of the deeper subsurface. By analyses of seismic anisotropy, which investigates the splitting of shear waves traversing an anisotropic medium (so-called shear wave splitting) conclusions ...
    Description: thesis
    Keywords: 551.1 ; 550 ; TSY 200 ; Antarktis {Geophysik}
    Language: German
    Type: monograph , publishedVersion
    Format: 150 S.
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  • 14
    Publication Date: 2021-03-29
    Description: Radiocarbon, reservoir age, ocean circulation, projection age, top-to-bottom age, B-P age. - In paleoceanography and paleoclimatology radiocarbon is frequently used to date carbonaceous samples of the past 50,000 years and as a proxy to reconstruct circulation states of the ocean. Temporal variations of the atmospheric radiocarbon concentration, caused by a varying radiocarbon production rate or changes in the global carbon cycle, lead to dating uncertainties and also limit the usability of radiocarbon as an oceanographic proxy. In order to analyze and correct the influence of varying atmospheric radiocarbon on the ocean, radiocarbon has been included as a tracer to a global climate model (University of Victoria Earth System Climate Model). This model was forced by the reconstructed atmospheric radiocarbon production rate, to predict differences between atmospheric and marine radiocarbon age, the so-called reservoir age, spatially and temporally.
    Description: thesis
    Keywords: 551.701 ; 550 ; Geochronologie einzelner Regionen ; Holozän ; Isotopengeologie ; Geochemische Kreislaufmodelle
    Language: German
    Type: monograph , publishedVersion
    Format: 124 S.
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  • 15
    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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