HR: 1340h
AN: PP33A-1544    [Abstracts]
TI: Temperature and [CO₃ ] Effects on Mg/Ca and Sr/Ca in the Benthic Foraminifera Species of Hoeglundina Elegans and Cibicidoides
AU: Lear, C H
EM: carrie@earth.cf.ac.uk
AF: School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3YE United Kingdom
AU: * Rosenthal, Y
EM: rosentha@marine.rutgers.edu
AF: Institute for Marine and Coastal Sciences, and Department of Geology, Rutgers University, 71 Dudley Road, New Brunswick, NJ 08901 United States
AU: Oppo, D W
EM: doppo@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Linsley, B K
EM: blinsley@albany.edu
AF: Department of Earth and Atmospheric Sciences, ES 351, University at Albany-SUNY, 1400 Washington Ave, Albany, NY 12222 United States
AB: Current core-top calibrations suggest that the temperature sensitivity of Mg/Ca in Cibicidoides sp. tests is essentially identical with the 10% increase in Mg/Ca per 1°C observed in many planktonic species. However, there is also evidence suggesting that non temperature-related effects may exert additional control on Mg/Ca in foraminiferal calcite. Here we use core-top samples from Atlantic (Little Bahama Banks, LBB; Arctic) and Pacific (Hawaii, and Indonesia) depth transects to assess the influence of bottom water temperature (BWT) and carbonate saturation levels on metal/Ca ratios in the aragonitic benthic foraminifer Hoeglundina elegans and calcitic Cibicidoides sp. We find that in situ CO₃ ion concentrations play an important role in determining the Mg/Ca ratios in Cibicidoides sp. and Mg/Ca and Sr/Ca in H. elegans. The CO₃ ion effect is limited, however, only to relatively low saturation levels, whereas at over-saturated levels, temperature exert the dominant effect on these metal ratios. Because we find no significant difference between results obtained on ``live'' and ``dead'' specimens, we propose that these differences are due to primary effects on metal uptake during test formations and not because of dissolution. Based on the new results we reappraise the Mg/Ca-temperature relationship of Cibicidoides sp. and propose a new calibration. We also propose that Sr/Ca and Mg/Ca in H. elegans tests can be used to reconstruct thermocline temperatures. Sr/Ca-thermometry in H. elegans may be especially useful in cases where the use of Mg/Ca thermometry in calcitic foraminfera has been compromised by contamination issues. In both cases, temperature estimates in low carbonate saturation levels may be grossly inaccurate.
DE: 4835 Marine inorganic chemistry (1050)
DE: 4924 Geochemical tracers
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005