HR: 11:20h
AN: PP42A-04    [Abstracts]
TI: Influences on the fractionation of calcium isotopes in planktonic foraminifera
AU: * Griffith, E M
EM: emgriffith@stanford.edu
AF: Stanford University, Department of Geological & Environmental Sciences Building 320, Room 118, Stanford, CA 94305, United States
AU: Paytan, A
EM: apaytan@ucsc.edu
AF: Stanford University, Department of Geological & Environmental Sciences Building 320, Room 118, Stanford, CA 94305, United States
AU: Paytan, A
EM: apaytan@ucsc.edu
AF: University of California Santa Cruz, Earth & Marine Sciences Bldg., Santa Cruz, CA 95064, United States
AU: Kozdon, R
EM: rkozdon@ifm-geomar.de
AF: Leibniz-Institut fur Meereswissenschaften IFM-GEOMAR, Wischhofsraße 1-3, Kiel, D- 24148, Germany
AU: Eisenhauer, A
EM: aeisenhauer@ifm-geomar.de
AF: Leibniz-Institut fur Meereswissenschaften IFM-GEOMAR, Wischhofsraße 1-3, Kiel, D- 24148, Germany
AU: Ravelo, A C
EM: acr@ucsc.edu
AF: University of California Santa Cruz, Earth & Marine Sciences Bldg., Santa Cruz, CA 95064, United States
AB: Foraminiferal Ca isotope ratios have been suggested as a paleotemperature proxy, however previous work indicates a range of possible sensitivities of foraminiferal Ca isotopes to temperature. Our results from coretop and sediment trap samples add to our knowledge of potential controls on the temperature dependence of Ca isotopic fractionation in planktonic foraminifera. This data is imperative for the application of this proxy interpretation of downcore Ca isotope records. Seven species of planktonic foraminifera from coretop sediments collectively exhibited a Ca temperature dependent fractionation of 0.013 permil per degree C. This is in agreement with previously published estimates for most species of planktonic foraminifera as well as biogenic and inorganic calcite and aragonite. Four species of planktonic foraminifera collected from a sediment trap showed a considerable amount of scatter and no consistent temperature dependent fractionation. Although foraminiferal tests are one of the most commonly used carriers of paleoclimatic and paleoceanographic data, the particular pathways and processes of biomineralization in foraminifera are not well known. It is difficult to distinguish between processes that ultimately control Ca and other elemental compositions in foraminiferal calcite. In particular, the chemistry of the solution from which foraminifera precipitate their test is not well defined. A one-box model (Elderfield et al., 1996) in which Ca isotopes are allowed to fractionate by Raleigh distillation from a biomineralization reservoir (internal pool) was used to constrain the isotopic composition of the original biomineralization Ca reservoir, assuming around 85% of the Ca reservoir is precipitated and the fractionation factor during precipitation is 0.9985 + 0.00002(T). To explain the foraminiferal Ca isotope data, this model indicates that the Ca isotopic composition of the biomineralization reservoir is offset from seawater (approximately -0.8 permil).
DE: 0419 Biomineralization
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 4870 Stable isotopes (0454, 1041)
DE: 4944 Micropaleontology (0459, 3030)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting