Refining Mg/Ca paleothermometry in foraminifera: Overcoming the dissolution problem with a flow-through leaching procedure

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The proponents will further test and develop a flow through analytical technique for the determination of Mg/Ca in planktonic forams, a proxy for sea surface temperature (SST). A problem with measured Mg/Ca in bulk dissolved samples of forams, is that dissolution can fractionate Mg/Ca. In addition, later calcification and contaminant phases can complicate the Mg/Ca signal. The flow through cleaning technique, using the ICPMS and time-resolved analysis (TRA), will allow monitoring of the Mg/Ca signal as the forams are slowly dissolved and analyzed. This technique is similar in principle to stepwise heating used for 40Ar/39Ar dating and is expected to distinguish between the early calcite formed nearest the surface and other unwanted signals. A pilot study of samples from two cores taken at ~900m and ~2000 at the Cocos Ridge show promising early results. TRA analysis of prepared samples of G. ruber, and G. sacculifer show high initial values of Mg/Ca thought to be the initially formed calcite. More calibration of the technique will be done for other samples, with comparisons to Mn contents and d18O. Finally, the new technique will be used to analyze SST in map and time-series back to the Last Glacial Maximum (LGM) in cores from the tropical and subtropical Pacific to resolve controversy about the role of the tropics in climate change.