HR: 11:50h
AN: PP42A-06    [Abstracts]
TI: Trace element (Mg, Sr, P, Ba and Cd) variability in single foraminifera and a possible new proxy for seawater phosphate
AU: * Newton, A
EM: a.newton@nature.com
AF: University of South Carolina, Department of Geological Sciences 701 Sumter St; EWS 617, Columbia, SC 29208, United States
AU: Kohn, M J
EM: mattkohn@boisestate.edu
AF: Boise State University, Department of Geosciences 1910 University Dr.; MS1535, Boise, ID 83725, United States
AU: Thunell, R C
EM: Thunell@geol.sc.edu
AF: University of South Carolina, Department of Geological Sciences 701 Sumter St; EWS 617, Columbia, SC 29208, United States
AB: Although the controls on the trace element composition in bulk foraminifera are reasonably well understood, elemental distributions in single foraminiferal shells are less well constrained. Here we present Mg/Ca, Sr/Ca, Ba/Ca, Cd/Ca, and P/Ca ratios from zoning profiles across the surfaces of several species of planktonic and benthic foraminifera. Ablation conditions included a 213 nm laser operating at 5 Hz, a 12 μm spot, and a fluence of ~10J/cm²; ablated material was analyzed by using a single collector, magnetic sector ICP-MS in low resolution mode. Compositions were standardized against NIST612 glass, so absolute ratios are more poorly resolved than zoning patterns.

The nutrient proxies Ba, P and Cd (when detectable) commonly show considerable (5-10x) variability both between and within individual chambers; the temperature proxies Mg and Sr showed less variability (1-5x). Trace element concentrations are particularly high at chamber boundaries, suggesting that chamber boundary calicification concentrates trace elements. Covariation was significant among nutrient proxies, and between temperature proxies, but was weaker for nutrient vs. temperature proxies.

We also analyzed samples at various stages of a standard trace element cleaning procedure. Bulk Mg/Ca decreased strongly with increasingly aggressive cleaning measures, suggesting the removal of Mg-rich coatings and/or primary calcite. P/Ca values, however, appear unchanged, suggesting that P is not hosted in loosely associated organic matter, but contained within the calcite itself. Relatively high Na contents suggest a straightforward substitution of Ca+PO₄ for Na+CO₃ in the calcite lattice. The likely occurrence of inorganic PO₄ in foraminifera, the strong covariance of P/Ca with other nutrient proxies, and the ease of P measurement via ICP-MS, recommend P/Ca in foraminifera as a possible new proxy for seawater PO₄ chemistry.
DE: 0419 Biomineralization
DE: 1065 Major and trace element geochemistry
DE: 4845 Nutrients and nutrient cycling (0470, 1050)
DE: 4890 Zooplankton
DE: 4924 Geochemical tracers
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting