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A Cenozoic Record of Seawater Uranium in Fossil Corals

Gothmann, Anne M. and Higgins, John A. and Adkins, Jess F. and Broecker, Wally S. and Farley, Kenneth A. and McKeon, Ryan and Stolarski, Jarosław and Planavsky, Noah and Wang, Xiangli and Bender, Michael L. (2019) A Cenozoic Record of Seawater Uranium in Fossil Corals. Geochimica et Cosmochimica Acta, 250 . pp. 173-190. ISSN 0016-7037. doi:10.1016/j.gca.2019.01.039.

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We measured U/Ca ratios, ^4He concentrations, ^(234)U/^(238)U, and ^(238)U/^(235)U in a subset of well-preserved aragonitic scleractinian fossil corals previously described by Gothmann et al. (2015). Comparisons of measured fossil coral He/U ages with the stratigraphic age demonstrate that well-preserved coral aragonite retains most or all of its radiogenic He for 10’s of millions of years. Such samples must be largely or entirely free of alteration, including neomorphism. Measurements of ^(234)U/^(238)U and ^(238)U/^(235)U further help to characterize the fidelity with which the original U concentration has been preserved. Analyses of fossil coral U/Ca show that the seawater U/Ca ratio rose by a factor of 4-5 between the Early Cenozoic and today. Possible explanations for the observed increase include (1) the stabilization of U in seawater due to an increase in seawater [CO_3^(2-)], and a resulting increase in UO_2-CO_3 complexation as originally suggested by Broecker (1971); (2) a decrease in the rate of low-temperature hydrothermal alteration from Early Cenozoic to present, leading to a diminished U sink and higher seawater [U]; or (3) a decrease in uranium removal in reducing sediments, again leading to higher seawater [U].

Item Type:Article
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Adkins, Jess F.0000-0002-3174-5190
Farley, Kenneth A.0000-0002-7846-7546
Additional Information:© 2019 Published by Elsevier Ltd. Received 9 August 2018, Accepted 30 January 2019, Available online 6 February 2019. We would like to thank Francois L.H. Tissot for helpful comments on multiple drafts of this manuscript as well as Associate Editor, Claudine Stirling, and an anonymous reviewer. We 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. Elizabeth Lundstrom (Princeton University) and Lindsey Hedges (California Institute of Technology) provided critical analytical support. We also thank Sarah Jane White (USGS), Francois Morel (Princeton University) and Will Amidon (Middlebury College) for helpful discussions that improved this manuscript.
Record Number:CaltechAUTHORS:20190206-103754732
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Official Citation:Anne M. Gothmann, John A. Higgins, Jess F. Adkins, Wally Broecker, Kenneth A. Farley, Ryan McKeon, Jarosław Stolarski, Noah Planavsky, Xiangli Wang, Michael L. Bender, A Cenozoic record of seawater uranium in fossil corals, Geochimica et Cosmochimica Acta, Volume 250, 2019, Pages 173-190, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92712
Deposited By: Tony Diaz
Deposited On:06 Feb 2019 18:52
Last Modified:16 Nov 2021 03:52

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