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Stable and Clumped Isotope Characterization of Authigenic Carbonates in Methane Cold Seep Environments

Thiagarajan, Nivedita and Crémière, Antoine and Blättler, Clara and Lepland, Aivo and Kirsimäe, Kalle and Higgins, John and Brunstad, Harald and Eiler, John (2020) Stable and Clumped Isotope Characterization of Authigenic Carbonates in Methane Cold Seep Environments. Geochimica et Cosmochimica Acta, 279 . pp. 204-219. ISSN 0016-7037. doi:10.1016/j.gca.2020.03.015.

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Cold seep environments are characterized by methane-rich fluid migration and discharge at the seafloor. These environments are also intimately linked to microbial communities, which oxidize methane anaerobically, increase alkalinity and promote authigenic carbonate precipitation. We have analyzed a suite of methane-derived authigenic carbonate (MDAC) crusts from the North and Barents Sea using stable and clumped isotopes (δ¹³C, δ¹⁸O, δ⁴⁴Ca, and Δ₄₇) to characterize the sources of fluids as well as the environment of carbonate authigenesis. We additionally assess the potential of MDACs as a Δ₄₇-based paleotemperature archive. The MDACs occur as three main textural-mineralogic types: micritic Mg-calcite cements, micritic aragonite cements and cavity filling aragonite cements. We find that micritic Mg-calcite cements have low δ¹³C_(VPDB) values (−30 to −47‰), high δ⁴⁴Ca_(SW) values (−0.4 to −0.8‰), and Δ₄₇-temperatures (0–6 °C) consistent with shallow sub-seafloor precipitation in isotopic equilibrium. Micritic aragonite cements and cavity filling aragonite cements both have a wider range in δ¹³C_(VPDB) values (−18 to −58‰), lower δ⁴⁴Ca_(SW) values (−0.8 to −1.6‰) and a larger range in Δ₄₇-based apparent temperatures (–2 – 25 °C) with samples displaying equilibrium and disequilibrium clumped isotope values. The range in apparent temperatures as well as δ⁴⁴Ca_(SW) values seen in the aragonite MDACs suggest two kinetic processes: a kinetic isotope effect (KIE) due to the incomplete equilibration of carbon and oxygen isotopes among DIC species from the different sources of DIC (i.e., seawater, methane-sourced DIC and DIC residual to CO₂ degassing or diffusion) and a KIE due to a fast, irreversible precipitation affecting the cations, particularly Ca, bound to carbonate mineral. Our results improve the understanding of kinetic effects on clumped isotope temperatures in MDACs and demonstrate how the multi-isotopic approach combined with textural-mineralogic criteria can be used to identify MDACs for accurate paleotemperature reconstructions.

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Crémière, Antoine0000-0001-7382-2097
Additional Information:© 2020 Published by Elsevier Ltd. Received 12 February 2019, Revised 7 March 2020, Accepted 11 March 2020, Available online 19 March 2020. This work was supported by the Research Council of Norway through the Petromaks2 - NORCRUST project (grant number 255150). 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.
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Research Council of Norway255150
Record Number:CaltechAUTHORS:20200319-153944096
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Official Citation:Nivedita Thiagarajan, Antoine Crémière, Clara Blättler, Aivo Lepland, Kalle Kirsimäe, John Higgins, Harald Brunstad, John Eiler, Stable and clumped isotope characterization of authigenic carbonates in methane cold seep environments, Geochimica et Cosmochimica Acta, Volume 279, 2020, Pages 204-219, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102006
Deposited By: Tony Diaz
Deposited On:19 Mar 2020 23:01
Last Modified:16 Nov 2021 18:07

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