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Carbonate clumped isotope variability in shallow water corals: Temperature dependence and growth-related vital effects

Saenger, Casey and Affek, Hagit P. and Felis, Thomas and Thiagarajan, Nivedita and Lough, Janice M. and Holcomb, Michael (2012) Carbonate clumped isotope variability in shallow water corals: Temperature dependence and growth-related vital effects. Geochimica et Cosmochimica Acta, 99 . pp. 224-242. ISSN 0016-7037. doi:10.1016/j.gca.2012.09.035.

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Geochemical variations in shallow water corals provide a valuable archive of paleoclimatic information. However, biological effects can complicate the interpretation of these proxies, forcing their application to rely on empirical calibrations. Carbonate clumped isotope thermometry (Δ_(47)) is a novel paleotemperature proxy based on the temperature dependent “clumping” of ^(13)C–^(18)O bonds. Similar Δ_(47)-temperature relationships in inorganically precipitated calcite and a suite of biogenic carbonates provide evidence that carbonate clumped isotope variability may record absolute temperature without a biological influence. However, large departures from expected values in the winter growth of a hermatypic coral provided early evidence for possible Δ_(47) vital effects. Here, we present the first systematic survey of Δ_(47) in shallow water corals. Sub-annual Red Sea Δ_(47) in two Porites corals shows a temperature dependence similar to inorganic precipitation experiments, but with a systematic offset toward higher Δ_(47) values that consistently underestimate temperature by ∼8 °C. Additional analyses of Porites, Siderastrea, Astrangia and Caryophyllia corals argue against a number of potential mechanisms as the leading cause for this apparent Δ_(47) vital effect including: salinity, organic matter contamination, alteration during sampling, the presence or absence of symbionts, and interlaboratory differences in analytical protocols. However, intra- and inter-coral comparisons suggest that the deviation from expected Δ_(47) increases with calcification rate. Theoretical calculations suggest this apparent link with calcification rate is inconsistent with pH-dependent changes in dissolved inorganic carbon speciation and with kinetic effects associated with CO_2 diffusion into the calcifying space. However, the link with calcification rate may be related to fractionation during the hydration/hydroxylation of CO_2 within the calcifying space. Although the vital effects we describe will complicate the interpretation of Δ_(47) as a paleothermometer in shallow water corals, it may still be a valuable paleoclimate proxy, particularly when applied as part of a multi-proxy approach.

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Additional Information:© 2012 Elsevier Ltd. Received 2 May 2012; accepted in revised form 19 September 2012; available online 28 September 2012. Associate Editor: Claire Rollion-Bard. We thank Gerry Olack, Dominic Colosi and Glendon Hunsinger of the Yale Earth System Center for Stable Isotopic Studies for their laboratory assistance. Also thanks to members of the Affek lab for discussion and access to their data. Daniel Schrag, Jess Adkins and Robert Halley generously donated coral samples. Eric Matson and Eric Lazo-Wasem provided valuable logistical support. This work was supported by the NOAA Climate and Global Change Postdoctoral Program for C.S. and National Science Foundation Grant NSF-EAR-0842482 to H.P.A. T.F. is supported by the DFG-Research Center/Excellence Cluster “The Ocean in the Earth System”.
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NOAA Climate and Global Change Postdoctoral ProgramUNSPECIFIED
DFG-Research Center/Excellence ClusterUNSPECIFIED
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Official Citation:Casey Saenger, Hagit P. Affek, Thomas Felis, Nivedita Thiagarajan, Janice M. Lough, Michael Holcomb, Carbonate clumped isotope variability in shallow water corals: Temperature dependence and growth-related vital effects, Geochimica et Cosmochimica Acta, Volume 99, 15 December 2012, Pages 224-242, ISSN 0016-7037, 10.1016/j.gca.2012.09.035. (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36162
Deposited By: Ruth Sustaita
Deposited On:04 Jan 2013 18:00
Last Modified:09 Nov 2021 23:20

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