Nonequilibrium clumped isotope signals in microbial methane

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Wang, David T.
Gruen, Danielle S.
Lollar, Barbara Sherwood
Hinrichs, Kai-Uwe
Stewart, Lucy C.
Holden, James F.
Hristov, Alexander N.
Pohlman, John W.
Morrill, Penny L.
Konneke, Martin
Delwiche, Kyle B.
Reeves, Eoghan P.
Sutcliffe, Chelsea N.
Ritter, Daniel J.
Seewald, Jeffrey S.
McIntosh, Jennifer C.
Hemond, Harold F.
Kubo, Michael D. Y.
Cardace, Dawn
Hoehler, Tori M.
Ono, Shuhei
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Methane is a key component in the global carbon cycle with a wide range of anthropogenic and natural sources. Although isotopic compositions of methane have traditionally aided source identification, the abundance of its multiply-substituted “clumped” isotopologues, e.g., 13CH3D, has recently emerged as a proxy for determining methane-formation temperatures; however, the impact of biological processes on methane’s clumped isotopologue signature is poorly constrained. We show that methanogenesis proceeding at relatively high rates in cattle, surface environments, and laboratory cultures exerts kinetic control on 13CH3D abundances and results in anomalously elevated formation temperature estimates. We demonstrate quantitatively that H2 availability accounts for this effect. Clumped methane thermometry can therefore provide constraints on the generation of methane in diverse settings, including continental serpentinization sites and ancient, deep groundwaters.
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of AAAS for personal use, not for redistribution. The definitive version was published in Science 348 (2015): 428-431, doi:10.1126/science.aaa4326.
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