HR: 0800h
AN: PP51C-1349    [Abstracts]
TI: Implications for Reconstructions of the Upper Ocean Stratification From Core-top Planktonic Foraminiferal Multispecies \delta$^{18}$O and Mg/Ca
AU: * Regenberg, M
EM: mregenberg@ifm-geomar.de
AF: Leibniz-Institute for Marine Sciences IFM-GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Steph, S
EM: ssteph@ifm-geomar.de
AF: Leibniz-Institute for Marine Sciences IFM-GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Tiedemann, R
AF: Leibniz-Institute for Marine Sciences IFM-GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Nuernberg, D
AF: Leibniz-Institute for Marine Sciences IFM-GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Dullo, W
AF: Leibniz-Institute for Marine Sciences IFM-GEOMAR, Wischhofstr. 1-3, Kiel, 24148 Germany
AB: As one of the most important features of the upper tropical Atlantic the depth of the seasonally varying thermocline increases from east to west as a function of tropical wind strength and oceanic heat transport. Upwelling in the east due to easterly trade winds, and equatorial divergent flow bring cool, nutrient-rich intermediate depth water to the surface, therefore creating steep vertical thermal gradients. The wind-induced westward flow of surface currents allows tropical warmer surface water to pile up in western parts of the basin beyond 30$^\circ$ W, resulting in the westward dip of the thermocline and the seasonally scarcely changing Western Atlantic Warm Water Pool. To monitor the variability in surface hydrography and vertical temperature gradients in tropical oceans, planktonic foraminifera are one of the most commonly used tools in paleoceanography. They live vertically dispersed in the upper water column, recording in their tests \delta$^{18}$O and Mg/Ca the ambient \delta$^{18}$O composition and temperature of the surrounding sea water. In the geological record, oxygen isotopes provide information about the calcification temperature and calcification depth of one species relative to another, usually without information on the absolute vertical depth of calcification, because for most species calcification depth varies depending on hydrography. Here, we present combined \delta$^{18}$O and Mg/Ca measurements of 9 planktonic foraminiferal species from 65 tropical sediment core-top samples spread from the E- to W-Atlantic and the Caribbean Sea. The chosen transect from about 15$^\circ$ S and 10$^\circ$ E to 20$^\circ$ N and 75$^\circ$ W follows the South Equatorial Current and the North Brazil Current and crosses the Caribbean Sea. Comparison of the isotopic and trace metal data, measured on the same organisms and mineral phases, with modern hydrographic data enable us to trace characteristic patterns of the modern upper ocean stratification and to estimate the absolute depth of calcification of planktonic foraminiferal species. However, the comparison of sediment surfaces with recent hydrography is a strict test of the usefulness of a paleoceanographic tool.
DE: 4825 Geochemistry
DE: 4855 Plankton
DE: 4870 Stable isotopes
DE: 4875 Trace elements
DE: 4572 Upper ocean processes
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting