HR: 13:55h
AN: PP13B-02    [Abstracts]
TI: Pleistocene Glaciation and the Stability of North Atlantic Thermohaline Circulation
AU: * Raymo, M E
EM: raymo@bu.edu
AF: Boston University, Dept. of Earth Sciences 685 Comm. Ave, Newton, MA 02215 United States
AU: Oppo, D W
EM: doppo@whoi.edu
AF: WHOI, Marine Geology and Geophysics Dept., Woods Hole, MA 02543 United States
AU: McManus, J F
EM: jmcmanus@whoi.edu
AF: WHOI, Marine Geology and Geophysics Dept., Woods Hole, MA 02543 United States
AB: Geochemical profiles from the North Atlantic Ocean suggest that the vertical $\delta13C$ structure of the water column at intermediate depths did not change significantly between glacial and interglacial time over much of the Pleistocene, despite large changes in ice volume and iceberg delivery from nearby landmasses. After the Mid-Pleistocene Transition (MPT), warmer interglaciations may have resulted in periodically (and present-day) open sea ice conditions in the Norwegian-Greenland Sea. The high $\delta13C$ deep water that forms in the NGS region today may be geologically unusual and restricted to the few extreme interglaciations of the late Pleistocene. Over most of the Pleistocene, Norwegian Sea Overflow Water appears to have had low $\delta13C$ values, similar to Southern Ocean Water, and is seen as a mid-depth low-$\delta13C$ layer between 1 and 2 km depth south of the Greenland-Scotland Ridge. If northern source deep waters can have variable $\delta13C$, then this likelihood must be considered when inferring past circulation changes from benthic $\delta13C$ records. The larger ice volumes attained after the MPT may also have resulted in the periodically large and rapid discharges of freshwater associated with Heinrich events. Only such extreme freshwater perturbations appear to be able to significantly disrupt the THC from its normal mode that characterizes most of the Pleistocene. With the modern configuration of land and ice, it seems unlikely that future alterations to high latitude run-off would constitute a density perturbation as large as a Heinrich event. The question remains whether proposed hydrographic changes at high latitudes would fall outside the range of the glacial-interglacial boundary conditions under which North Atlantic THC appears to have been relatively stable.
DE: 4267 Paleoceanography
DE: 4283 Water masses
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting