HR: 0800h
AN: PP21C-1571    [Abstracts]
TI: Natural variability of coral Cd/Ca using a novel isotope dilution ICP-MS method
AU: * Matthews, K A
EM: kam2@sas.upenn.edu
AF: Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA 19104 United States
AU: McDonough, W F
EM: mcdonoug@geol.umd.edu
AF: Department of Geology, University of Maryland, College Park, MD 20742 United States
AU: Grottoli, A G
EM: grottoli.1@osu.edu
AF: Department of Geological Sciences, Ohio State University, Columbus, OH 43210 United States
AB: Here we present a new method for the rapid and precise determination of Cd/Ca in coral skeleton using inductively coupled mass spectrometry (ICP-MS). This ratio has been shown to be a promising proxy for oceanic upwelling. This method uses isotope dilution for Cd determination and gravimetric standards with internal standardization for Ca determination. In addition, an ion exchange resin is used to separate the earth alkaline metals (Ca, Sr, Ba) from Cd to reduce the high total dissolved solids (TDS) while maintaining a strong Cd signal. Each sample is then processed as a pair, once for Ca (and Sr and Ba, if desired) and once for Cd. Although not yet explored, other possible elements that could be run in the Cd set include vanadium, zinc and manganese. Reproducibility with this method is comparable to other ICP-MS methods, yielding 1sd precision of ~2% and repeated analyses of reference materials (BCR-1, BHVO-1, W-2, GSR-6, JCp-1) fall within established ranges. The removal of TDS has a distinct advantage over other ICP-MS methods that use more concentrated coral solutions; reducing the introduction of high-concentration elements, such as Ca, Mg and Sr, to the mass spectrometer is necessary in a multi-use laboratory that requires low background at those masses. Currently sample size is <30mg (allows for duplicate measurements), which is similar to that used for coral Cd analysis via GFAAS, but with ICP-MS multiple elements can be measured simultaneously. Preliminary results from coral samples ( Pavona gigantea) in the seasonally-upwelling Gulf of Panama (Pacific) indicate that, while average Cd concentrations are higher during upwelling than nonupwelling, the range due to natural variability among the P. gigantea individuals renders this difference statistically insignificant. These results suggest that for P. gigantea, much of the variability observed in single-core coral records of Cd/Ca may not be caused by upwelling. Additional results from different depths and species will also be presented to further address the impact of the natural variability of coral Cd/Ca and the implications for paleoclimate reconstruction using this proxy.
DE: 4215 Climate and interannual variability (1616, 1635, 3305, 3309, 4513)
DE: 4279 Upwelling and convergences (4964)
DE: 4808 Chemical tracers
DE: 4875 Trace elements (0489)
DE: 4894 Instruments, sensors, and techniques
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005