HR: 0800h
AN: PP31C-0537    [Abstracts]
TI: ‘Clumped isotope' thermometry in benthic foraminifera and ostracods: A novel tool for reconstructing deep-ocean temperatures
AU: Eiler, J
EM: eiler@caltech.edu
AF: California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, United States
AU: * Tripati, A
EM: atri02@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, United States
AU: * Tripati, A
EM: atri02@gps.caltech.edu
AF: University of Cambridge, Downing Street, Cambridge, Cam CB2 3EQ, United Kingdom
AB: The benthic oxygen isotope (δ¹⁸O) record is an archive of past deep-water temperatures and ice volume. The carbonate ‘clumped isotope' thermometer provides a new technique for reconstructing temperature. It is based on the principle that the proportion of ¹³C-¹⁸O bonds in carbonate minerals is temperature-dependent [1-3]. Unlike other temperature proxies, the clumping of heavy isotopes into bonds with each other is independent of the isotopic composition of the water in which the mineral precipitated. Abundances of ¹³C-¹⁸O bonds in carbonates are determined by measuring Δ₄₇ values of CO₂ extracted from carbonate by acid digestion; Δ₄₇ values reflect enrichments, in per mil, of ¹³C¹⁸O¹⁶O in product CO₂ relative to the amount expected by random chance. Paired measurements of Δ₄₇ and δ¹⁸O can potentially yield accurate and quantitative determinations of past temperature and seawater δ¹⁸O. We have measured the Δ₄₇ values of core-top benthic foraminifera and ostracods. Preliminary results show that multiple species with different ecologies exhibit the same temperature dependence as inorganic calcite [1]. In contrast to the benthic Mg/Ca thermometer [4], there does not appear to be a discernable influence of carbonate ion concentration on the Δ₄₇ composition of benthic foraminifera (e.g. a carbonate ion effect). Calibration data will be shown for several benthic foraminifera, including the epifaunal taxa Planulina wuellerstorfi, Cibicidoides mundulus, Cibicidoides pachyderma, Hoeglundina elegans, Gyroidina sp. and the infaunal taxa Oridorsalis umbonatus, Melonis pompilioides, and Uvigerina sp. In addition, we will discuss results for the ostracod genus Krithe sp. and mixed ostracod species. [1] Wang, Z., Schauble, E., and Eiler, J., 2004, Equilibrium thermodynamics of multiply substituted isotopologues of molecular gases, Geochimica et Cosmochimica Acta, 68, 4779-4797l [2] Schauble, E., Ghosh, P., and Eiler, J. 2006, Preferential formation of ¹³C-¹⁸O bonds in carbonate minerals, estimated using first-principles lattice dynamics, Geochimica et Cosmochimica Acta, 70, 2510-2529. [3] Ghosh, P., Adkins, J., Affek, H, Balta, B., Guo, W., Schauble, E, Schrag, D. and Eiler, J., 2006, ¹³C–¹⁸O bonds in carbonate minerals: A new kind of paleothermometer, Geochimica et Cosmochimica Acta, 70, 1439–1456. [4] Elderfield, H., J. Yu, P. Anand, T. Kiefer, and B. Nyland, 2006, Calibrations for benthic foraminiferal Mg/Ca palaeothermometry and the carbonate ion hypothesis. Earth and Planetary Science Letters, 250, 633-649.
DE: 4924 Geochemical tracers
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting