HR: 1340h
AN: PP33A-1550    [Abstracts]
TI: Meridional Overturning Circulation in the South Atlantic at the Last Glacial Maximum
AU: * Lynch-Stieglitz, J
EM: jean@eas.gatech.edu
AF: School of Earth and Atmospheric Sciences, Georgia Institue of Technology, Atlanta, GA 30332 United States
AU: Curry, W B
EM: wcurry@whoi.edu
AF: Dept. of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Oppo, D W
EM: doppo@whoi.edu
AF: Dept. of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Ninneman, U N
EM: Ulysses.Ninnemann@geo.uib.no
AF: Department of Earth Science, University of Bergen, Bergen, 5007 Norway
AU: Charles, C D
EM: ccharles@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD 9500 Gilman Drive, La Jolla, CA 92093 United States
AU: Munson, J
EM: jmunson@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD 9500 Gilman Drive, La Jolla, CA 92093 United States
AB: The geostrophic shear associated with the meridional overturning circulation is reflected in the difference in density between the eastern and western margins of the ocean basin. Here we examine how the density difference across 30°S in the upper 2 km of the Atlantic Ocean (and thus the magnitude of the shear associated with the overturning circulation) has changed between the last glacial maximum and the present. We use oxygen isotope measurements on benthic foraminifera to reconstruct density. Today, the density in upper and intermediate waters along the eastern margin in the South Atlantic is greater than along the western margin, reflecting the vertical shear associated with the northward flow of surface and intermediate waters and the southward flowing North Atlantic Deep Waters below. The greater density along the eastern margin is reflected in the higher δ¹⁸O values for surface sediment benthic foraminifera than those found on the western margin for the upper 2 km. For the last glacial maximum the available data indicate that the eastern margin foraminifera had similar δ¹⁸O to those on the western margin between 1-2 km, and that the gradient was reversed relative to today with the higher δ¹⁸O values in the western margin benthic foraminifera above 1 km. Assuming that this reversal in benthic foraminiferal δ¹⁸O gradient reflects a reversal in sea water density gradient, these data are not consistent with a vigorous but shallower overturning cell in which northward flowing surface waters are balanced by the southward export of Glacial North Atlantic Intermediate Water. Scenarios with a vigorous northward flow of Antarctic Intermediate Water balanced by a southward flow of surface waters in the South Atlantic (e.g. Weaver et al., 2003) are consistent with the ocean margin δ¹⁸O data.
DE: 4532 General circulation (1218, 1222)
DE: 4870 Stable isotopes (0454, 1041)
DE: 4926 Glacial
DE: 4962 Thermohaline
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005