HR: 14:10h
AN: PP13B-03 INVITED     [Abstracts]
TI: Glacial Water Mass Geometry and the Distribution of $\delta^{13}$C of $\Sigma$CO$_{2}$ in the Western Atlantic Ocean
AU: * Curry, W B
EM: wcurry@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Oppo, D W
EM: doppo@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AB: Oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa {\it Cibicidoides} and {\it Planulina} from twenty five piston cores, gravity cores and multi-cores from the Brazil margin. The cores span water depths from about 400 m to 3000 m and intersect the major water masses in this region. The Holocene and glacial bathymetric profiles of benthic foraminifera $\delta^{13}$C show significant differences. The Holocene bathymetric profile along the Brazil margin shows the presence of North Atlantic Deep Water as a local maximum in $\delta^{13}$C centered at about 2500 m, intersecting the northward flowing water masses Antarctic Intermediate Water/Circum-polar Deep Water and Antarctic Bottom Water. The glacial bathymetric profile of $\delta^{13}$C of $\Sigma$CO$_{2}$ requires the presence of three distinct water masses in the glacial Atlantic Ocean: a shallow ($\sim$1000 m), southern-source water mass with an end-member $\delta^{13}$C value of about 0.3-0.5 $\permil$ VPDB, a mid-depth ($\sim$1500 m), northern-source water mass with an end-member value of about 1.5 $\permil$, and a deep ($>$2000 m), southern-source water with an end-member value of $<$-0.2 $\permil$ and perhaps as low as the -0.9 $\permil$ values observed in the South Atlantic sector of the Southern Ocean [Ninnemann and Charles, 2002]. The origins of the water masses are supported by the meridional gradients in benthic foraminiferal $\delta^{18}$O: at similar depths in the water column, the southern water masses are colder, less salty and have a higher benthic foraminiferal $\delta^{18}$O value than the water mass originating in the north. Although there is evidence for significant aging and mixing of the water mass along its trajectory, the mid-depth northern-source water mass crossed the equator and could still be identified as a unique water mass as far south as 30$\deg$ S. In contrast, the shallow, southern-source water mass did not exert a significant influence in the northern subtropical Atlantic. These new data fill a critical gap in the South Atlantic Ocean and provide the motivation for updating the classic glacial Atlantic $\delta^{13}$C transect of Duplessy {\it et al.} [1988]. A revised glacial section of western Atlantic $\delta^{13}$C of $\Sigma$CO$_{2}$ documents the positions and gradients among these intermediate and deep water masses. The strong hydrographic gradients observed below 2000 m in the North and South Atlantic most likely result from mixing along the mid-Atlantic Ridge system between water masses of very different end-member $\delta^{13}$C composition.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 4283 Water masses
DE: 4532 General circulation
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting