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^(13)C–^(18)O isotope signatures and ‘clumped isotope’ thermometry in foraminifera and coccoliths

Tripati, Aradhna K. and Eagle, Robert A. and Thiagarajan, Nivedita and Gagnon, Alexander C. and Bauch, Henning and Halloran, Paul R. and Eiler, John M. (2010) ^(13)C–^(18)O isotope signatures and ‘clumped isotope’ thermometry in foraminifera and coccoliths. Geochimica et Cosmochimica Acta, 74 (20). pp. 5697-5717. ISSN 0016-7037.

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Accurate constraints on past ocean temperatures and compositions are critical for documenting climate change and resolving its causes. Most proxies for temperature are not thermodynamically based, appear to be subject to biological processes, require regional calibrations, and/or are influenced by fluid composition. As a result, their interpretation becomes uncertain when they are applied in settings not necessarily resembling those in which they were empirically calibrated. Independent proxies for past temperature could provide an important means of testing and/or expanding on existing reconstructions. Here we report measurements of abundances of stable isotopologues of calcitic and aragonitic benthic and planktic foraminifera and coccoliths, relate those abundances to independently estimated growth temperatures, and discuss the possible scope of equilibrium and kinetic isotope effects. The proportions of ^(13)C–^(18)O bonds in these samples exhibits a temperature dependence that is generally similar to that previously been reported for inorganic calcite and other biologically precipitated carbonate-containing minerals (apatite from fish, reptile, and mammal teeth; calcitic brachiopods and molluscs; aragonitic coral and mollusks). Most species that exhibit non-equilibrium ^(18)O/^(16)O (δ^(18)O) and ^(13)C/^(12)C (δ^(13)C) ratios are characterized by ^(13)C–^(18)O bond abundances that are similar to inorganic calcite and are generally indistinguishable from apparent equilibrium, with possible exceptions among benthic foraminiferal samples from the Arctic Ocean where temperatures are near-freezing. Observed isotope ratios in biogenic carbonates can be explained if carbonate minerals generally preserve a state of ordering that reflects the extent of isotopic equilibration of the dissolved inorganic carbon species.

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Additional Information:© 2010 Elsevier Ltd. Received 12 August 2009; accepted 1 July 2010. Associate editor: Clark Johnson. Available online 15 July 2010. Support for this project was provided by the UCLA Division of Physical Sciences, NERC, NSF, and Magdalene College. Samples for this study were obtained from the Godwin Laboratory sample archives through David Thornalley, Harry Elderfield, Mike Hall, and James Rolfe; from Lowell Stott, the Scripps Institute of Oceanography collections through Richard Norris, and the Ocean Drilling Program. We would like to thank Jeannie Booth and Linda Booth for assistance with sample preparation; Jeremy Boyce, Andy Cohen, Simon Crowhurst, Allegra LeGrande, Gavin Schmidt, and Laurence Yeung for discussion of this work and comments on a draft of this manuscript; Thibault de Garidel- Thoron for provision of published data from MD97-2138; and Jess Adkins, Daniel Cicerone, David Dettman, Harry Elderfield, Jonathan Erez, Weifu Guo, Katherine Hungtington, Ted McConnaughey, Nele Meckler, Jay Quade, Michael Reddy, Edwin Schauble, Philippe Van Cappellen, and Bruce Watson for discussion of this work. We also thank three anonymous reviewers and the associate editor for their constructive comments on this manuscript.
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UCLA Division of Physical SciencesUNSPECIFIED
Natural Environment Research Council (NERC)UNSPECIFIED
Magdalene CollegeUNSPECIFIED
Issue or Number:20
Record Number:CaltechAUTHORS:20101027-143651374
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20566
Deposited By: Tony Diaz
Deposited On:13 Nov 2010 03:19
Last Modified:03 Oct 2019 02:12

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