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Brachiopod δ³⁴S_(CAS) microanalyses indicate a dynamic, climate-influenced Permo-Carboniferous sulfur cycle

Johnson, Daniel L. and Grossman, Ethan L. and Webb, Samuel M. and Adkins, Jess F. (2020) Brachiopod δ³⁴S_(CAS) microanalyses indicate a dynamic, climate-influenced Permo-Carboniferous sulfur cycle. Earth and Planetary Science Letters, 546 . Art. No. 116428. ISSN 0012-821X. doi:10.1016/j.epsl.2020.116428.

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Early isotopic studies of sulfate in carbonate minerals (carbonate associated sulfate; CAS) suggested that carbonates can provide a reliable, well-dated archive of the marine sulfur cycle through time. However, subsequent research has shown that diagenetic alteration can impose highly heterogeneous CAS sulfur isotopic compositions (δ³⁴S_(CAS)) among different carbonate phases within sediments. Such alteration necessitates targeted sampling of well-preserved, primary carbonate phases. Here, we present a new record of Carboniferous and Early Permian brachiopod δ³⁴S_(CAS) generated from over 130 measurements of microsampled brachiopod shells. Our record refines existing brachiopod δ³⁴S_(CAS) records and confirms a large, ∼6.5‰ δ³⁴S_(CAS) decrease in the Early Carboniferous. Importantly, the record also features a novel 3–5‰ increase in δ³⁴S_(CAS) near the Serpukhovian-Bashkirian boundary (323.4 Ma) that coincides with carbonate δ¹³C and δ¹⁸O increases. Variability in δ³⁴S_(CAS) is minor both within (≤0.3‰) and among (≤2‰) individual co-depositional brachiopod specimens. A taxon-specific δ³⁴S_(CAS) offset is present one species (Composita subtilita) that also exhibits a δ¹³C offset, supporting the existence of biological “vital effects” on δ³⁴S_(CAS). Geologic evidence and mathematical modeling of the Permo-Carboniferous carbon and sulfur cycles suggest that changes in the burial ratio of organic carbon to pyrite sulfur (RC:S) are insufficient to explain the observed mid-Carboniferous δ³⁴S_(CAS) record. We find that changes in the ³⁴S depletion of pyrite relative to seawater sulfate (ε³⁴) or in the δ³⁴S of the input to the ocean (δ³⁴S_(in)) are also needed. Large additions of O₂ from organic carbon burial during the Permo-Carboniferous cannot be entirely compensated for with sulfur cycle changes; lower than modern late Visean pO₂ and/or additional O₂ sinks are needed to keep pO₂ at plausible levels. Based on the geologic context surrounding our record's mid-Carboniferous δ³⁴S_(CAS) increase, we advocate for simultaneous changes in pyrite burial, ε³⁴, and δ³⁴S_(in), driven by sea level or tectonically induced changes in environments of sulfur burial, as a viable mechanism to produce rapid seawater δ³⁴S changes.

Item Type:Article
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URLURL TypeDescription
Johnson, Daniel L.0000-0002-7443-1546
Grossman, Ethan L.0000-0002-1045-6939
Adkins, Jess F.0000-0002-3174-5190
Additional Information:© 2020 Elsevier B.V. Received 6 December 2019, Revised 17 June 2020, Accepted 18 June 2020, Available online 7 July 2020. Ted Present, Guillaume Paris, Jared Marske, Nathan Dalleska, Sharon Bone, and Courtney Roach provided valuable analytical support. We also thank the editor and two anonymous reviewers for thoughtful suggestions that substantially improved this manuscript. This work was supported by National Science Foundation (NSF) grants OCE-1559215, OCE-1737404, OCE-1450528, and MGG-1834492; NASA prime grant NNN12AA01C; Change Happens Foundation; and Grantham Foundation awards to JFA. DLJ additionally thanks the NSF for support through a Graduate Research Fellowship. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funding AgencyGrant Number
Change Happens FoundationUNSPECIFIED
Grantham FoundationUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Department of Energy (DOE)DE-AC02-76SF00515
Subject Keywords:biogeochemical cycles; sulfur isotope geochemistry; carbonate associated sulfate; brachiopods; Permo-Carboniferous
Record Number:CaltechAUTHORS:20200714-093504749
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Official Citation:Daniel L. Johnson, Ethan L. Grossman, Samuel M. Webb, Jess F. Adkins, Brachiopod δ34SCAS microanalyses indicate a dynamic, climate-influenced Permo-Carboniferous sulfur cycle, Earth and Planetary Science Letters, Volume 546, 2020, 116428, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104374
Deposited By: Tony Diaz
Deposited On:14 Jul 2020 17:28
Last Modified:16 Nov 2021 18:31

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