HR: 08:15h
AN: PP41E-02    [Abstracts]
TI: The Mg/Ca-Temperature Relationship of Benthic Foraminiferal Calcite: New Core-top Calibrations in the <4°C Temperature Range
AU: * Healey, S L
EM: shealey@geol.sc.edu
AF: University of South Carolina Department of Geological Sciences, 700 Sumter St., Columbia, SC 29208, United States
AU: Thunell, R C
EM: thunell@geol.sc.edu
AF: University of South Carolina Department of Geological Sciences, 700 Sumter St., Columbia, SC 29208, United States
AU: Corliss, B H
EM: bruce.corliss@duke.edu
AF: Duke University Department of Earth and Ocean Sciences, Nicholas School of the Environment and Earth Sciences, Durham, NC 27706, United States
AB: Calcite magnesium/ calcium ratios were determined for four species of benthic foraminifera ( Cibicidoides wuellerstorfi, Cibicidoides kullenbergi, Oridorsalis umbonatus and Pyrgo murrhina) from core-top samples collected from the Atlantic, Indian, and Pacific oceans where modern bottom water temperatures are less than 4°C. Mg/Ca of all four species increase with increasing temperature, and the Mg/Ca: temperature relationship does not appear to be necessarily exponential. Mg/Ca of C. kullenbergi is consistently higher than C. wuellerstorfi, implying differences in the uptake of Mg by different species within this genus. The observed Mg/Ca for C. wuellerstorfi at temperatures less than 3°C is lower than those predicted from published Mg/Ca: temperature relationships derived for Cibicidoides spp. at higher temperatures. Previous studies have attributed this change in the Mg/Ca-temperature relationship of C. wuellerstorfi to the effect of decreased carbonate ion saturation (Δ[CO₃^2-]) on Mg/Ca at low temperatures. A relationship between the (Δ[CO₃^2-] and Mg/Ca of 0.0083±0.002 (mmol/mol)/ (μmol/kg) has been established for C. wuellerstorfi from this study. Down-core Mg/Ca and δ¹⁸O values for the last 40,000 years were determined for C. wuellerstorfi from eastern equatorial Pacific core TR163-14 in order to carry out a sensitivity study of various Mg/Ca paleotemperature equations. Comparison of temperature estimates derived from three different equations indicate a 1.0 to 2.3°C difference between estimated temperatures, demonstrating the need for caution when choosing a Mg/Ca: temperature equation to estimate past temperatures, as the Mg/Ca-temperature relationship of benthic foraminiferal calcite is considerably different above and below ~3°C.
DE: 0419 Biomineralization
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1065 Major and trace element geochemistry
DE: 4944 Micropaleontology (0459, 3030)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting