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A Cenozoic record of seawater Mg isotopes in well-preserved fossil corals

Gothmann, Anne M. and Stolarski, Jarosław and Adkins, Jess F. and Higgins, John A. (2017) A Cenozoic record of seawater Mg isotopes in well-preserved fossil corals. Geology, 45 (11). pp. 1039-1042. ISSN 0091-7613.

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Reconstructions of seawater Mg isotopic composition (δ^(26)Mg) can provide novel insights into the processes that control the major ion chemistry of seawater over geologic time scales. A key period of interest is the Cenozoic (ca. 65 Ma to today), during which the Mg/Ca ratio of seawater increased by a factor of 2–3. However, two published records of seawater δ^(26)Mg over the Cenozoic disagree, making it difficult to draw conclusions about mechanisms driving seawater Mg/Ca change over the past 65 m.y. Here we present a new record of seawater δ^(26)Mg from a set of well-preserved fossil corals, ranging in age from Paleocene to Recent. Fossil coral δ^(26)Mg decreases by ∼0.3‰ between the early Cenozoic and the Oligocene, then increases by ∼0.15‰ between the Oligocene and present, in strong agreement with the published record derived from bulk pelagic carbonate. Together with this existing record, our fossil coral data suggest that the rise in [Mg]_(seawater) over the Cenozoic was mainly driven by an increase in Mg silicate weathering or a decline in Mg uptake in marine silicates. In contrast, we suggest that changes in the rate of carbonate weathering and dolomite formation likely played a minor, but not insignificant, role in the global Mg cycle over the Cenozoic.

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Adkins, Jess F.0000-0002-3174-5190
Additional Information:© 2017 Geological Society of America. Manuscript received 14 June 2017; Revised manuscript received 13 August 2017; Manuscript accepted 18 August 2017; Published: October 02, 2017. We thank Michael Bender and Casey Saenger for their valuable thoughts on this manuscript, and Elizabeth Lundstrom for assistance with Mg isotope measurements. We acknowledge the Princeton BP Amoco Carbon Mitigation Initiative and the Frank Harrison Tuttle Memorial Fund for Invertebrate Studies for their generous support. We thank Dan Schrag, Josh Wimpenny, and an anonymous reviewer for comments that greatly improved this manuscript.
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Frank Harrison Tuttle Memorial FundUNSPECIFIED
Issue or Number:11
Record Number:CaltechAUTHORS:20171031-145632026
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Official Citation:Anne M. Gothmann, Jarosław Stolarski, Jess F. Adkins, John A. Higgins; A Cenozoic record of seawater Mg isotopes in well-preserved fossil corals. Geology ; 45 (11): 1039–1042. doi:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:82819
Deposited By: Tony Diaz
Deposited On:31 Oct 2017 22:04
Last Modified:24 Feb 2020 10:30

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