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Calcium isotopes in scleractinian fossil corals since the Mesozoic: Implications for vital effects and biomineralization through time

Gothmann, Anne M. and Bender, Michael L. and Blättler, Clara L. and Swart, Peter K. and Giri, Sharmila J. and Adkins, Jess F. and Stolarski, Jarosław and Higgins, John A. (2016) Calcium isotopes in scleractinian fossil corals since the Mesozoic: Implications for vital effects and biomineralization through time. Earth and Planetary Science Letters, 444 . pp. 205-214. ISSN 0012-821X. doi:10.1016/j.epsl.2016.03.012.

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We present a Cenozoic record of δ^(44/40)Ca from well preserved scleractinian fossil corals, as well as fossil coral δ^(44/40)Ca data from two time periods during the Mesozoic (84 and 160 Ma). To complement the coral data, we also extend existing bulk pelagic carbonate records back to ∼80 Ma. The same fossil corals used for this study were previously shown to be excellently preserved, and to be faithful archives of past seawater Mg/Ca and Sr/Ca since ∼200 Ma (Gothmann et al., 2015). We find that the δ^(44/40)Ca compositions of bulk pelagic carbonates from ODP Site 807 (Ontong Java Plateau) and DSDP Site 516 (Rio Grande Rise) have not varied by more than ∼±0.20‰ over the last ∼80 Myr. In contrast, the δ^(44/40)Ca compositions of Mesozoic and Early Cenozoic fossil corals are ∼1‰ lighter than those of modern corals. The observed change in coral δ^(44/40)Ca does not likely reflect secular variations in seawater δ^(44/40)Ca. Instead, we propose that it reflects a vital effect of calcification – specifically, a sensitivity of coral Ca isotope discrimination to changing seawater [Ca] and/or pH. Support for this hypothesis comes from the presence of an empirical correlation between our coral δ^(44/40)Ca record and records of seawater [Ca] and pH since the Mesozoic (Lowenstein et al., 2003 and Hönisch et al., 2012). We explore various mechanisms that could give rise to such a vital effect, including: (1) changes in calcification rate, (2) changes in proton pumping in exchange for Ca^(2+), (3) variable Rayleigh distillation from an isolated calcifying fluid, and (4) changes in the calcium mass balance of the extracellular calcifying fluid (termed here the “leaky Ca model”). We test for the dependence of seawater δ^(44/40)Ca on external seawater [Ca] by measuring the δ^(44/40)Ca of cultured corals grown in seawater solutions with [Ca] ranging from 10 to 15 mmol/kg. Corals grown under elevated [Ca] conditions show a slight, ∼0.15‰ depletion of δ^(44/40)Ca at higher seawater [Ca] – a supportive but not definitive result.

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Adkins, Jess F.0000-0002-3174-5190
Additional Information:© 2016 Elsevier B.V. Received 24 September 2015; Received in revised form 27 February 2016; Accepted 6 March 2016; Available online 7 April 2016. We would like to thank Stephen Cairns and Tim Coffer (Smithsonian Institution), Linda Ivany (Syracuse University), Roger Portell (Florida Museum of Natural History), Anne Cohen and Bill Thompson (WHOI), the USGS, and Gregory Dietl (Paleontological Research Institution) for loaning samples. We would also like to thank Alex Gagnon for helpful discussions and Elizabeth Lundstrom, Tom Capo and Phil Gillette for experimental assistance. We would like to acknowledge the Princeton BP Amoco Carbon Mitigation Initiative and the Frank Harrison Tuttle Memorial Fund for Invertebrate studies for their generous support.
Funding AgencyGrant Number
Princeton BP Amoco Carbon Mitigation InitiativeUNSPECIFIED
Frank Harrison Tuttle Memorial Fund for Invertebrate StudiesUNSPECIFIED
Subject Keywords:Ca isotopes; scleractinian coral; vital effects; bulk carbonate; culture experiment; seawater chemistry
Record Number:CaltechAUTHORS:20160603-073625755
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Official Citation:Anne M. Gothmann, Michael L. Bender, Clara L. Blättler, Peter K. Swart, Sharmila J. Giri, Jess F. Adkins, Jarosław Stolarski, John A. Higgins, Calcium isotopes in scleractinian fossil corals since the Mesozoic: Implications for vital effects and biomineralization through time, Earth and Planetary Science Letters, Volume 444, 15 June 2016, Pages 205-214, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67634
Deposited By: Tony Diaz
Deposited On:03 Jun 2016 17:39
Last Modified:11 Nov 2021 03:52

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