HR: 16:30h
AN: PP44A-03    [Abstracts]
TI: Glacial ITCZ Shifts Recorded by Tropical Salinity Reconstructions in the Pacific and Caribbean
AU: * Spero, H J
EM: spero@geology.ucdavis.edu
AF: University of California Davis, Department of Geology, Davis, CA 95616 United States
AU: Schmidt, M W
EM: schmidt@geology.ucdavis.edu
AF: University of California Davis, Department of Geology, Davis, CA 95616 United States
AU: Lea, D W
EM: lea@geol.ucsb.edu
AF: University of California Santa Barbara, Department of Geological Sciences and the Marine Science Institute, Santa Barbara, CA 93106 United States
AB: A variety of data from terrestrial, marine and modeling studies indicate that the tropical Atlantic and Pacific ITCZ was shifted considerably south of its current position during the last glacial period. The effect of such a shift on the glacial ocean would be to increase surface salinity (relative to today) in regions that are currently influenced by the ITCZ and to decrease salinity in regions that are currently south of the modern ITCZ but within the influence of the glacial ITCZ. Here we compare a previously published 380 ka \delta$^{18}$O$_{sw}$ reconstruction (a proxy for salinity) for the western equatorial Pacific (WEP) at ODP Site 806B ($0.33\deg$N, $159.34\deg$E) (Lea et al. 2000) with a new Caribbean \delta$^{18}$O$_{sw}$ reconstruction at ODP Site 999A ($12.75\deg$N, $78.75\deg$W) that was derived from Mg/Ca (a proxy for SST) and \delta$^{18}$O data from a surface dwelling foraminifera, {\it Globigerinoides ruber}. These reconstructions indicate the WEP was considerably fresher during past glacial periods with surface \delta$^{18}$O$_{sw}$ 0.3 to 0.4 \permil lower than today after removal of ice volume. Using modern \delta$^{18}$O$_{sw}$ vs salinity relationships, this geochemical change suggests glacial surface salinities in the WEP at Site 806B were ~1-1.5 psu lower than today. In contrast, Caribbean surface waters were much saltier during the last glacial period with \delta$^{18}$O$_{sw}$ 0.5 \permil higher than modern after removal of ice volume. This \delta$^{18}$O$_{sw}$ shift translates to a glacial surface salinity $>$2 psu higher than today (after the influence of ice volume was removed). Reconstruction of surface salinities across 3 glacial cycles back to 380 ka at these two sites demonstrate that the Caribbean and WEP were antiphased with large salinity differences during glacials and nominal differences during interglacials. Tropical western Pacific sediment trap data indicate the maximum {\it G. ruber} flux is during the summer months. Hence, we interpret these data to indicate that the glacial summer ITCZ was located over the equator in the WEP, considerably farther south than its current position at $8-10\deg$N. In contrast, the elevated Caribbean salinities support terrestrial and coastal Cariaco Basin data that indicate the ITCZ was situated over the over South America during the summer months. We are optimistic that future \delta$^{18}$O$_{sw}$ records from adjacent tropical sites will permit us to reconstruct the continuous migration of the ITCZ through time.
DE: 4231 Equatorial oceanography
DE: 4267 Paleoceanography
DE: 1833 Hydroclimatology
DE: 1620 Climate dynamics (3309)
DE: 1635 Oceans (4203)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting