The Evolution and Impact of Weddell Sea Deep Water
The interaction between the Antarctic Ice Sheet and the Southern Ocean is of major importance for changes in Earth’s climate. The Antarctic Ice Sheet is largely marine based and grounded below sea level, which makes it especially vulnerable for sea-level forcing and ocean warming. In turn, the Southern Ocean overturning circulation is partially driven by deep water formation along the Antarctic continent, which is strongly modulated by interactions of surface water with the floating ice shelves. These processes are crucial for the evolution of the climate in the past and future, but remain generally poorly constrained. In this dissertation, the evolution and impact of Antarctic Bottom Water sourced from the Weddell Sea is investigated by use of deep sea sediments recovered in the Scotia Sea. The study covers the last 450,000 years, which are characterized by several major climate transitions from glacial to interglacial stages. These transitions are accompanied by millennial-scale increases in atmospheric CO2, a rise in temperature, and global sea-level rise. The evolution of formation and export of deep water sourced from the Weddell Sea is examined with a multi-proxy approach to obtain a thorough understanding of the sedimentation dynamics under various climatic boundary conditions. This is possible through reconstruction of changes in productivity (by use of Th normalized opal flux, biogenic Ba), vertical vs. horizontal sedimentation processes (Th normalized focusing), bottom water oxygenation (authigenic U), sediment provenance (detrital radiogenic Nd and Pb isotopes), water mass provenance (authigenic Pb isotopes), and identification of marine forward and reverse silicate weathering processes (dissolved stable Si and radiogenic Sr isotopes, fine grained K’/Ar ages). Overall, the novel findings of this dissertation demonstrate that the coupling between the Antarctic Ice Sheet and Southern Ocean circulation is crucial for major climate transitions and abrupt climatic events. Understanding the underlying processes and interactions is of utmost importance in order to distinguish regime shifts from natural variability and to predict the future pathway of ocean circulation under the influence of anthropogenic climate change.
Southern Ocean, Antarctica, Antarctic Ice Sheet, Paleoceanography, Paleoclimate, Late Pleistocene, Deep Sea Sediments, Isotopes, Geochemistry
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