HR: 0800h
AN: PP41A-0633    [Abstracts]
TI: Multiproxy Evidence of the Role of the Vertical Structure of the Southern Ocean in Global Climate Change
AU: * Anderson, L D
EM: linda@ucsc.edu
AF: Institute of Marine Sciences, 1156 High St., University of California, Santa Cruz, CA 95064 United States
AB: The modern Southern Ocean controls a major portion of the global intermediate and deep water chemical and physical characteristics. `Old' nutrient-enriched, alkaline water masses are formed as a result of influx of waters from the Pacific (some via the Indonesian seaway from the Indian), Indian, and Atlantic oceans; multiple cycles around Antarctica; and minimal ventilation. Subducted waters from the Weddell and Ross seas as well as the Adélie Coast are mixed as a consequence of the intense flow through the Drake Passage over the irregular topography within the Scotia Sea. The deep vertical mixing has at least three consequences for the global carbon cycle 1. cold and nutrient- enriched, subducted thermocline water; 2. alkaline, CaCO₃-corrosive deep; and 3. minimal burial of organic carbon within the Southern Ocean despite high seasonal productivity. However, without a well-developed Antarctic Circumpolar Current, the Southern Ocean hydrography would be significantly different from modern. This study uses a suite of proxies to characterize hydrographic factors that could facilitate organic carbon burial. Reactive phosphorus mass accumulation rates (MARs) provides an assessment of organic carbon burial, excess barium MARs an evaluation of export productivity, and their ratio, an indication of relative efficiency of organic carbon burial to export productivity. In addition, biogenic components (CaCO₃ and opal MARs) indicate upwelled- water characteristics and redox chemistry of sediments (U and Mn enrichment) provide deep water characteristics. Multiproxy evidence from sub-Antarctic Agulhas Ridge (Ocean Drilling Program Site 1090) around the Eocene/ Oligocene and Oligocene/Miocene climatic shifts suggest that the Southern Ocean had much more variable water mass characteristics. The vertical structure may provide a mechanism for increased organic carbon burial that facilitated atmospheric carbon dioxide drawdown, sensitized the earth system to external forcing.
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4910 Astronomical forcing
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005