HR: 0830h
AN: PP11A-0211    [PDF]
TI: Paired Mg/Ca and $\delta^{18}$O in Planktonic Foraminifers from Caribbean and (Sub-)Tropical South Atlantic Core-Top Sediments - Assessing the Dissolution Effect
AU: * Regenberg, M
EM: mregenberg@geomar.de
AF: GEOMAR Research Center for Marine Geosciences, Wischhofstr. 1-3, Kiel, D-24148 Germany
AU: Nuernberg, D
EM: dnuernberg@geomar.de
AF: GEOMAR Research Center for Marine Geosciences, Wischhofstr. 1-3, Kiel, D-24148 Germany
AU: Steph, S
EM: ssteph@geomar.de
AF: GEOMAR Research Center for Marine Geosciences, Wischhofstr. 1-3, Kiel, D-24148 Germany
AU: Groeneveld, J
EM: jgroeneveld@geomar.de
AF: GEOMAR Research Center for Marine Geosciences, Wischhofstr. 1-3, Kiel, D-24148 Germany
AU: Tiedemann, R
EM: rtiedemann@geomar.de
AF: GEOMAR Research Center for Marine Geosciences, Wischhofstr. 1-3, Kiel, D-24148 Germany
AU: Mulitza, S
EM: smul@palmod.uni-bremen.de
AF: University of Bremen, Klagenfurterstr., Bremen, D-28359 Germany
AB: Reliable sea surface temperatures (SST) are crucial to any reconstruction and modeling of past ocean salinity and density, water column stratification, thermohaline circulation, and ice volume. Currently, foraminiferal Mg/Ca paleothermometry is widely used for reconstructing past SST, although modern species-specific Mg/Ca {\it vs.} SST calibrations still suffer from inconsistencies, and the impact of calcite dissolution needs still to be better defined. Here, we present paired Mg/Ca and $\delta$ $^{18}$O data of the spinose mixed layer dwelling foraminiferal species {\it Globigerinoides ruber} and {\it Globigerinoides sacculifer}, and the nonspinose thermocline dwelling {\it Neogloboquadrina dutertrei} gathered from Caribbean and South Atlantic core-top sediments. Samples cover a wide range of water depths from 1000-4600 m, thus extending existing data sets to more shallow water depths. In particular, the Caribbean study allows to assess dissolution effects since spatial temperature variations are minimal. Caribbean specimens of {\it G. ruber} have highest Mg/Ca ratios, while Mg/Ca in {\it G. sacculifer} is lower by 10-12%, and {\it N. dutertrei} is even lower by ca. 50%. {\it G. ruber} shows a wide range in Mg/Ca concentrations from 3.6-5.8 mmol/mol, while the Mg/Ca range in {\it G. sacculifer} and {\it N. dutertei} is smaller (1.4 and 1.5 mmol/mol, respectively). $\delta$ $^{18}$O values of the deep-dwelling {\it N. dutertrei} are consistently more positive than those of the shallow-living {\it G. sacculifer} and {\it G. ruber}. All species exhibit stable Mg/Ca ratios down to species-specific water depth levels. {\it N. dutertrei} and {\it G. sacculifer} start loosing Mg below ca. 3-3.5 km water depth, whereas for {\it G. ruber}, Mg is being removed f rom the tests far above 3 km water depth. The according $\delta$ $^{18}$O data of all species consistently become more positive with increasing water depth, although the strongest change is seen in tests of {\it G. ruber}. From these data it can be noted that {\it G. ruber} is most sensitive to dissolution (up to 15-20% decrease in foraminiferal test Mg/Ca per km), whereas {\it N. dutrei} is the most resistent (25-30% decrease in Mg/Ca per km water depth). Our results, therefore, are in contrast to previously published data from other ocean areas. Based on these results we develop species-specific Mg/Ca {\it vs.} SST calibrations for the Caribbean and the (sub-)tropical Atlantic, which consider the effect of increased dissolution with increased water depth.
DE: 3030 Micropaleontology
DE: 4267 Paleoceanography
DE: 4808 Chemical tracers
DE: 4875 Trace elements
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting