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Sulfur isotope fractionation between aqueous and carbonate-associated sulfate in abiotic calcite and aragonite

Barkan, Yigal and Paris, Guillaume and Webb, Samuel M. and Adkins, Jess F. and Halevy, Itay (2020) Sulfur isotope fractionation between aqueous and carbonate-associated sulfate in abiotic calcite and aragonite. Geochimica et Cosmochimica Acta, 280 . pp. 317-339. ISSN 0016-7037. doi:10.1016/j.gca.2020.03.022.

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Sulfate (SO₄²⁻) incorporated into calcium carbonate minerals enables measurements of sulfur (S) isotope ratios in carbonate rocks. This Carbonate Associated Sulfate (CAS) in marine carbonate minerals is thought to faithfully represent the S isotope composition of the seawater sulfate incorporated into the mineral, with little or no S isotope fractionation in the process. However, comparison between different calcifying species reveals both positive and negative S isotope fractionation between CAS and seawater sulfate, and a large range of S isotope ratios can be found within a single rock sample, depending on the component measured. To better understand the isotopic effects associated with sulfate incorporation into carbonate minerals, we precipitated inorganic calcite and aragonite over a range covering more than two orders of magnitude of sulfate concentration and precipitation rate. Coupled measurements of CAS concentration, S isotope composition and X-ray absorption near-edge spectra (XANES) permit characterization and explanation of the observed dependence of S isotope fractionation between CAS and aqueous sulfate (CAS-SO₄²⁻ isotope fractionation) on sulfate concentration and precipitation rate. In aragonite, the CAS-SO₄²⁻ isotope fractionation is 1.0±0.3‰ and independent of the sulfate (and CAS) concentration. In contrast, the CAS-SO₄²⁻ isotope fractionation in calcite covaries strongly with the sulfate concentration and weakly with the precipitation rate, between values of 1.3±0.1 and 3.1±0.6‰. We suggest that the correlation between aqueous sulfate concentration and CAS-SO₄²⁻– isotope fractionation in calcite reflects a dependence of the equilibrium S isotope fractionation on the concentration of CAS, through the effect of the sulfate impurity on the carbonate mineral’s energetic state.

Item Type:Article
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URLURL TypeDescription
Barkan, Yigal0000-0001-6907-5850
Paris, Guillaume0000-0001-8368-1224
Adkins, Jess F.0000-0002-3174-5190
Additional Information:© 2020 Published by Elsevier Ltd. Received 25 July 2019, Accepted 16 March 2020, Available online 24 March 2020. We thank Ziv Sade and Nir Galili for discussions. I.H. acknowledges support from a European Research Council Starting Grant (No. 337183). Part of this work was supported by the Tellus program from CNRS/INSU. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.
Funding AgencyGrant Number
European Research Council (ERC)337183
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Institut national des sciences de l'Univers (INSU)UNSPECIFIED
Department of Energy (DOE)DE-AC02-76SF00515
Record Number:CaltechAUTHORS:20200324-101330481
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Official Citation:Yigal Barkan, Guillaume Paris, Samuel M. Webb, Jess F. Adkins, Itay Halevy, Sulfur isotope fractionation between aqueous and carbonate-associated sulfate in abiotic calcite and aragonite, Geochimica et Cosmochimica Acta, Volume 280, 2020, Pages 317-339, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102077
Deposited By: Tony Diaz
Deposited On:24 Mar 2020 18:07
Last Modified:16 Nov 2021 18:08

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