| dc.description.abstract | The Southern Ocean (SO) plays an essential role in the global circulation of oceanic water masses making it a powerful regulator of Earth’s climate. The distribution of water masses across the Pacific, Atlantic and Indian Ocean is mainly driven by the Antarctic Circumpolar Current (ACC). Antarctic BottomWater (AABW) is a prominent example of such a water mass. Being formed near the Antarctic continental shelf it is carried into the bottom regions of the global oceans by the ACC. Covering vast parts of the deep oceans, the cold and dense mass of AABW is an important factor for the oceanic uptake of excess atmospheric heat and carbon dioxide and thus provides a vital counterbalance to climate change. Consequently, changes in magnitude of AABW production are directly relatable to climate variations and, in consideration of the drastic global warming that has taken place during the
recent decades, worth investigating. To this end, Quaternary bottom currents in the open Pacific SO were reconstructed based on a particle size analysis conducted on two sediment cores (PS58/271-1 and PS58/273-1, ANT-XVIII/5a). The aim of the paleocurrent analysis was to make an assessment on how AABW production varies over time, how these variations relate to changing climate conditions and the nature of potential underlying factors. In general, the bottom currents at the study location are very weak (<5 cm s-1), implying that the higher accumulation rates detected at site PS58/271-1 must be due to stronger currents (focussing: increased material transport due to more energetic flow). The results reveal that on a glacial-interglacial timescale (<102 ka) bottom currents are mainly susceptible to bottom water production by brine rejection. Enhanced sea ice production during decreasing glacial temperatures intensifies the magnitude of AABW. Long-term changes throughout the Pleistocene (>102 ka), on the other hand, are more strongly dominated by bottom water production underneath the Filchner-Ronne Ice Shelf (FRIS) in the Weddell Sea through supercooling. A gradual grounding of the ice shelf with decreasing Pleistocene temperatures inhibits the magnitude of AABW. Owing to the large distance between study site and the Weddell Sea, the influence of FRIS-related bottom water production is assumed to be subordinate, making brine rejection the overall dominant factor of AABW production in the Pacific SO. In order to explain the visible influence of the grounding FRIS on long time scales, however, the assumption is made that sea ice formation has been relatively invariant throughout this period of time. It is concluded that global warming may reduce AABW formation in the Pacific SO which in turn would have a negative effect on the heat capacity of the ocean and Earth’s climate, thus closing a positive feedback loop. | |
