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^(13)C–^(18)O bonds in carbonate minerals: A new kind of paleothermometer

Ghosh, Prosenjit and Adkins, Jess and Affek, Hagit and Balta, Brian and Guo, Weifu and Schauble, Edwin A. and Schrag, Dan and Eiler, John M. (2006) ^(13)C–^(18)O bonds in carbonate minerals: A new kind of paleothermometer. Geochimica et Cosmochimica Acta, 70 (6). pp. 1439-1456. ISSN 0016-7037. doi:10.1016/j.gca.2005.11.014.

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The abundance of the doubly substituted CO_2 isotopologue, ^(13)C^(18)O^(16)O, in CO_2 produced by phosphoric acid digestion of synthetic, inorganic calcite and natural, biogenic aragonite is proportional to the concentration of ^(13)C–^(18)O bonds in reactant carbonate, and the concentration of these bonds is a function of the temperature of carbonate growth. This proportionality can be described between 1 and 50 °C by the function: Δ_(47) = 0.0592 • 10^6 • T^(−2) − 0.02, where Δ_(47) is the enrichment, in per mil, of ^(13)C^(18)O^(16)O in CO_2 relative to the amount expected for a stochastic (random) distribution of isotopes among all CO_2 isotopologues, and T is the temperature in Kelvin. This relationship can be used for a new kind of carbonate paleothermometry, where the temperature-dependent property of interest is the state of ordering of ^(13)C and ^(18)O in the carbonate lattice (i.e., bound together vs. separated into different CO_3^(2−) units), and not the bulk δ^(18)O or δ^(13)C values. Current analytical methods limit precision of this thermometer to ca. ± 2 °C, 1σ. A key feature of this thermometer is that it is thermodynamically based, like the traditional carbonate–water paleothermometer, and so is suitable for interpolation and even modest extrapolation, yet is rigorously independent of the δ^(18)O of water and δ^(13)C of DIC from which carbonate grew. Thus, this technique can be applied to parts of the geological record where the stable isotope compositions of waters are unknown. Moreover, simultaneous determinations of Δ_(47) and δ^(18)O for carbonates will constrain the δ^(18)O of water from which they grew.

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Adkins, Jess0000-0002-3174-5190
Additional Information:© 2005 Elsevier Inc. Received 2 August 2005; accepted 10 November 2005. Associate editor: Miryam Bar-Matthews. Available online 3 February 2006. This study was conducted in response to Michael Bender's good-natured prodding of J.M.E. and J.F.A.; we thank him for his insightful instincts and persistence. We gratefully acknowledge the help of Lisa Welp, who measured the d18O values of water from which we grew inorganic calcites, Ma Chi, who helped with XRD analyses of synthetic carbonates, and Dr. Willi Brand, who provided aliquots of MAR-J1 carbonate standard. We also thank the Smithsonian Institute for lending us deep-sea coral samples. This work made use of an instrument purchased with the help of NSF Grant EAR-0220066 and the Packard Foundation, and benefited from salary support provided by NSF Grant EAR-0345905.
Group:Caltech Tectonics Observatory
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Packard FoundationUNSPECIFIED
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Caltech Tectonics Observatory57
Issue or Number:6
Record Number:CaltechAUTHORS:20101124-091221004
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:21014
Deposited By: Tony Diaz
Deposited On:24 Nov 2010 18:45
Last Modified:09 Nov 2021 00:05

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