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  • In the unglaciated areas of Antarctica, lake sediments act as archives of the regional environmental and climatic history. In most cases, the records are restricted to the Holocene. Amongst the few exceptions are lakes in the McMurdo Dry Valleys, southern Victoria Land, which are known to have remained mostly ice-free during the Last Glacial Maximum. Within the scope of an U.S.-American-German expedition in austral summer 2002/2003, several sediment cores were recovered from the three major lakes in the Taylor Valley: lakes Fryxell, Hoare, and Bonney. In order to reconstruct the late Quaternary regional environmental and climate history, sedimentological, biogeochemical, mineralogical, and chronological investigations were conducted on the sediment sequences recovered from Lake Hoare (core Lz1020) and East Lake Bonney (core Lz1023) within the scope of this thesis. Sediment cores from Lake Hoare with a maximum length of 2.3 m mainly consist of coarse-grained material and penetrate back into the late Weichselian, when Taylor Valley was occupied by the large proglacial Lake Washburn. This lake was dammed by the advanced Ross Sea ice sheet at the valley outlet and was mainly fed by meltwater of the ice sheet. During the Pleistocene-Holocene transition, enhanced evaporation led to a significant lake level drop of Lake Washburn ...,thesis,
    Data Types:
    • Document
  • Dinoflagellate cysts, paleoceanography, paleoenvironment, Late Quaternary, Norwegian-Greenland Sea. - Dinoflagellate cysts have been investigated in nine short sediment cores as well as two long sediment cores from the Norwegian-Greenland Sea and the North Atlantic to reconstruct the surface water paleoenvironment of the last climatic cycle and the Holocene. Holocene sea-surface temperatures and salinities during summer and winter and the extent of sea-ice cover were reconstructed. On the Rockall Plateau, higher cyst concentrations indicating favourable conditions and increased productivity only occur during parts of stage 5, 4-2, and the Holocene. Only sparse occurrences of dinocysts have been observed in the Norwegian-Greenland Sea before 10000 yr BP. Later, high abundances of O. centrocarpum and N. labyrinthus indicate the increased inflow of relatively warm Atlantic. A change in dominance of these species as well as a distinct increase in cyst concentrations marks the onset of the recent circulation system. In the Norwegian Sea, O. centrocarpum dominates the assemblages since about 7000 yr BP, while assemblages in the Iceland and the Greenland Sea are more complex due to the influence of different surface currents.,thesis,
    Data Types:
    • Document
  • Nonsteady-state Diagenesis, Equatorial Atlantic, Rock-magnetic and Geochemical Multiproxy Approach, XRF Core Scanner, Fe Redox, Magnetite Dissolution. - This thesis investigates 25 Late Quaternary sediment records from the central Equatorial Atlantic by rock magnetic, geochemical and stratigraphical methods. The work was performed in the framework of the Collaborative Research Center 261 ‘The South Atlantic in the Late Quaternary: Reconstruction of Material Budgets and Current Systems’ funded by the Deutsche Forschungsgemeinschaft. The main objective was to analyze and distinguish terrigenous and diagenetic proxysignatures, in particular of rock magnetic parameters. All cores were correlated and dated on basis of their carbonate, iron and rock magnetic records. Magnetite coarsening and partial depletion was observed in glacial organic-rich layers, most intensely during oxygen isotope stages 6, 10 and 12. Non-magnetic and magnetic iron mineral enrichments were found below and at former and active Fe(II) / Fe(III) redox boundaries. Various new proxies quantifying magnetite reduction (ratio of Fe to magnetic susceptibility, ratio of non-ferrimagnetic to total magnetic susceptibility) and authigenesis (ratio of Fe to magnetic susceptibility) were established and found to be highly sensitive indicators of past redox conditions. Comparing these signals with the organic carbon records, it was shown, that rock magnetic, carbon and carbonate records in most parts ...,thesis,
    Data Types:
    • Document