HR: 09:00h
AN: PP51F-05    [Abstracts]
TI: A 3 Million Year physical Record of the Antarctic Circumpolar Current: Results from ODP Site 1101 and Comparison with Other Records
AU: * Hassold, N J
EM: nhassold@umich.edu
AF: Department of Geological Sciences, 2534 C.C. Little Building 1100 North University Ave. University of Michigan, Ann Arbor, MI 48109-1005 United States
AU: Rea, D K
EM: davidrea@umich.edu
AF: Department of Geological Sciences, 2534 C.C. Little Building 1100 North University Ave. University of Michigan, Ann Arbor, MI 48109-1005 United States
AU: van der Pluijm, B A
EM: vdpluijm@umcih.edu
AF: Department of Geological Sciences, 2534 C.C. Little Building 1100 North University Ave. University of Michigan, Ann Arbor, MI 48109-1005 United States
AU: Pares, J M
EM: jmpares@umich.edu
AF: Department of Geological Sciences, 2534 C.C. Little Building 1100 North University Ave. University of Michigan, Ann Arbor, MI 48109-1005 United States
AB: Ocean circulation and climate are intimately connected, as the oceans are a major mechanism of heat transport between latitudes, with the result that changes in circulation accompany climate change. After a brief warm period in the early Pliocene, continued global cooling led to ice sheet formation in the Northern Hemisphere and the ensuing Northern Hemisphere Glaciation. The Southern Ocean is the main area of mixing of waters from the Pacific, Indian and Atlantic Oceans and is, therefore, a proxy of circulation changes. As its primary current, the Antarctic Circumpolar Current (ACC) transports the largest volume of water (and heat) of any current on the planet. It extends to the sea floor, entraining incoming sediments, that are deposited along the flanks of topographical highs. These sediment drifts provide a sensitive record of ACC flow and, when close to Antarctica, a record of glacial activity. ODP Leg 178 drilled a series of drift deposits along the Pacific continental slope of the Antarctic Peninsula. Magnetic fabric analysis (Anisotropy of Magnetic Susceptibility, 211 samples) and grain size distribution determination (132 samples) on sediment from Site 1101, spanning the last 3 my, provide a proxy record of current strength. Mass Accumulation Rates (MAR) of terrigenous sediment, averaging about 7 g/cm2/ky, decrease at 2.5 Ma and then gradually increase before decreasing again around 0.75 Ma. Silica MAR values decrease gradually from 3 Ma to around 1.8 Ma and remain fairly constant at about 4 g/cm2/ky through the Quaternary. The MAR of the > 63 μm fraction has multiple peaks throughout the time period studied, which we interpret as evidence of ice sheet activity as recorded by ice-rafted debris. The magnetic fabric, which we use as a proxy for current strength, shows a moderate degree of fluctuation that gradually declines over time, in agreement with work by Joseph et al. (2002) on samples from the Kerguelen Plateau and our recent work at ODP Site 1095, located 450 km to the southwest of Site 1101. This gradual reduction in current strength and changes in ice-rafting imply a decoupling of the current strength from conditions of fluctuating ice cover on the Antarctic Peninsula, showing that these different parts of the climate system are responding to different forcings.
DE: 4207 Arctic and Antarctic oceanography (9310, 9315)
DE: 4999 General or miscellaneous
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005