HR: 1340h
AN: PP43B-1263    [Abstracts]
TI: Carbonate `clumped isotope' thermometry in planktonic foraminifera and coccoliths
AU: * Tripati, A
EM: atri02@esc.cam.ac.uk
AF: University of Cambridge, Downing Street, Cambridge, Cam CB23EQ, United Kingdom
AU: * Tripati, A
EM: atri02@esc.cam.ac.uk
AF: California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, United States
AU: Thiagarajan, N
EM: nivedita@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, United States
AU: Eiler, J
EM: eiler@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, United States
AB: Constraints on past ocean temperatures are critical for documenting climate change and resolving its causes. The carbonate ‘clumped isotope' thermometer is a novel tool for the reconstruction of ocean temperatures. ‘Clumped isotope' thermometry in general relies on the principle that ordering, or ‘clumping', of heavy isotopes into bonds with or near each other in molecules, minerals or organic moieties is a temperature dependent phenomenon [1]. Carbonate clumped isotope thermometry in particular examines the proportion of ¹³C and ¹⁸O that are bound to each other within the carbonate mineral lattice [2,3]. Unlike other temperature proxies, the proportion of ¹³C-¹⁸O bonds in carbonates is independent of the isotopic composition of water in which the carbonate grew. In practice, this thermometer is based on analyses of ¹³C¹⁸O¹⁶O in CO₂ produced by acid digestion of carbonates, which are reported using the variable, ‘Δ₄₇' — a measure of the enrichment, in per mil, of ¹³C¹⁸O¹⁶O above the amount expected for a random distribution of isotopes. We have made the first Δ₄₇ measurements of core-top planktonic foraminifera and coccoliths. Our initial results show that multiple species with different ecologies exhibit the same temperature dependence as inorganic calcite. We will present calibration data for mixed coccolith assemblages and multiple species of planktonic foraminifera, including: Globigerina bulloides, Neogloboquadrina dutertrei, Globigerinoides sacculifer, G. ruber, G. inflata, Globorotalia menardii, G. truncatulinoides, G. hirsuta, Globigerinella aequilateralis, and Pulleniatina obliquiloculata. In addition, data for core-top samples from a depth transect on the Ontong- Java Plateau in the Pacific Ocean will be used to assess the impact of dissolution on the Δ₄₇ of CO₂ evolved from marine carbonates. [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.
DE: 4924 Geochemical tracers
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting