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Carbonic anhydrase, coral calcification and a new model of stable isotope vital effects

Chen, Sang and Gagnon, Alexander C. and Adkins, Jess F. (2018) Carbonic anhydrase, coral calcification and a new model of stable isotope vital effects. Geochimica et Cosmochimica Acta, 236 . pp. 179-197. ISSN 0016-7037. doi:10.1016/j.gca.2018.02.032.

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The stable isotope compositions of biogenic carbonates have been used for paleoceanographic and paleoclimatic reconstructions for decades, and produced some of the most iconic records in the field. However, we still lack a fully mechanistic understanding of the stable isotope proxies, especially the biological overprint on the environmental signals termed “vital effects”. A ubiquitous feature of stable isotope vital effects in marine calcifying organisms is a strong correlation between δ¹⁸O and δ¹³C in a range of values that are depleted from inorganic calcite/aragonite. Two mechanisms have been proposed to explain this correlation, one based on kinetic isotope effects during CO₂(aq)-HCO₃⁻ inter-conversion, the other based on equilibrium isotope exchange during pH dependent speciation of the dissolved inorganic carbon (DIC) pool. Neither mechanism explains all the stable isotope features observed in biogenic carbonates. Here we present a fully kinetic model of biomineralization and its isotope effects using deep-sea corals as a test organism. A key component of our model is the consideration of the enzyme carbonic anhydrase in catalyzing the CO₂(aq)-HCO₃⁻ inter-conversion reactions in the extracellular calcifying fluid (ECF). We find that the amount of carbonic anhydrase not only modulates the carbonate chemistry of the calcifying fluid, but also helps explain the slope of the δ¹⁸O-δ¹³C correlation. Differences in CA activity in the biomineralization process can possibly explain the observed range of δ¹⁸O-δ¹³C slopes in different calcifying organisms. A mechanistic understanding of stable isotope vital effects with numerical models can help us develop better paleoceanographic tracers.

Item Type:Article
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URLURL TypeDescription
Chen, Sang0000-0001-8941-0791
Adkins, Jess F.0000-0002-3174-5190
Additional Information:© 2018 Elsevier Ltd. Received 13 June 2017, Accepted 16 February 2018, Available online 2 March 2018. This work received support from NSF grant P2C2-1503129. S.C. would like to acknowledge financial support from the China Scholarship Council for Ph.D. study at Caltech. We would also like to thank James Watkins for sharing his Matlab code for the oxygen isotope calculations. We are indebted to editors Tom Marchitto and Ros Rickaby for feedback on the original manuscript. Ted McConnaughey, Vanni Aloisi and an anonymous reviewer provided constructive comments that helped clarify key points of the paper. We dedicate this work to Harry Elderfield for his pioneering contributions to the study of vital effects in biogenic carbonates and many fruitful conversations over the years about the lives of the small and calcareous.
Group:Division of Geological and Planetary Sciences
Funding AgencyGrant Number
China Scholarship CouncilUNSPECIFIED
Subject Keywords:stable isotope vital effects; δ18O-δ13C slope; kinetic isotope effects; carbonic anhydrase; deep-sea corals
Record Number:CaltechAUTHORS:20180302-082405447
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Official Citation:Sang Chen, Alexander C. Gagnon, Jess F. Adkins, Carbonic anhydrase, coral calcification and a new model of stable isotope vital effects, Geochimica et Cosmochimica Acta, Volume 236, 2018, Pages 179-197, ISSN 0016-7037,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85056
Deposited By: Tony Diaz
Deposited On:02 Mar 2018 16:30
Last Modified:11 Apr 2023 20:38

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