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The Relative Abundances of Resolved 12CH2D2 and 13CH3D and Mechanisms Controlling Isotopic Bond Ordering in Abiotic and Biotic Methane Gases

Author(s): Young, Edward D; Kohl, Issaku E; Sherwood Lollar, Barbara; Etiope, Giuseppe; Rumble, Douglas; et al

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dc.contributor.authorYoung, Edward D-
dc.contributor.authorKohl, Issaku E-
dc.contributor.authorSherwood Lollar, Barbara-
dc.contributor.authorEtiope, Giuseppe-
dc.contributor.authorRumble, Douglas-
dc.contributor.authorLi (李姝宁), Shuning-
dc.contributor.authorHaghnegahdar, Mojhgan A-
dc.contributor.authorSchauble, Edwin A-
dc.contributor.authorMcCain, Kaitlyn A-
dc.contributor.authorFoustoukos, Dionysis I-
dc.contributor.authorSutclife, Chelsea-
dc.contributor.authorWarr, Oliver-
dc.contributor.authorBallentine, Chris J-
dc.contributor.authorOnstott, Tullis C-
dc.contributor.authorHosgormez, Hakan-
dc.contributor.authorNeubeck, Anna-
dc.contributor.authorMarques, José M-
dc.contributor.authorPérez-Rodríguez, Ileana-
dc.contributor.authorRowe, AR-
dc.contributor.authorLaRowe, Douglas E-
dc.contributor.authorMagnabosco, C-
dc.contributor.authorYeung, Laurence Y-
dc.contributor.authorAsh, Jeanine L-
dc.contributor.authorBryndzia, L Taras-
dc.identifier.citationYoung, Edward D., Issaku E. Kohl, B. Sherwood Lollar, Giuseppe Etiope, Douglas Rumble, Shuning Li, Mojhgan A. Haghnegahdar et al. "The Relative Abundances of Resolved 12 CH 2 D 2 and 13 CH 3 D and Mechanisms Controlling Isotopic Bond Ordering in Abiotic and Biotic Methane Gases." Geochimica et Cosmochimica Acta 203 (2016): 235-264. doi:10.1016/j.gca.2016.12.041.en_US
dc.description.abstractWe report measurements of resolved 12CH2D2 and 13CH3D at natural abundances in a variety of methane gases produced naturally and in the laboratory. The ability to resolve 12CH2D2 from 13CH3D provides unprecedented insights into the origin and evolution of CH4. The results identify conditions under which either isotopic bond order disequilibrium or equilibrium are expected. Where equilibrium obtains, concordant Δ12CH2D2 and Δ13CH3D temperatures can be used reliably for thermometry. We find that concordant temperatures do not always match previous hypotheses based on indirect estimates of temperature of formation nor temperatures derived from CH4/H2 D/H exchange, underscoring the importance of reliable thermometry based on the CH4 molecules themselves. Where Δ12CH2D2 and Δ13CH3D values are inconsistent with thermodynamic equilibrium, temperatures of formation derived from these species are spurious. In such situations, while formation temperatures are unavailable, disequilibrium isotopologue ratios nonetheless provide novel information about the formation mechanism of the gas and the presence or absence of multiple sources or sinks. In particular, disequilibrium isotopologue ratios may provide the means for differentiating between methane produced by abiotic synthesis vs. biological processes. Deficits in 12CH2D2 compared with equilibrium values in CH4 gas made by surface-catalyzed abiotic reactions are so large as to point towards a quantum tunneling origin. Tunneling also accounts for the more moderate depletions in 13CH3D that accompany the low 12CH2D2 abundances produced by abiotic reactions. The tunneling signature may prove to be an important tracer of abiotic methane formation, especially where it is preserved by dissolution of gas in cool hydrothermal systems (e.g., Mars). Isotopologue signatures of abiotic methane production can be erased by infiltration of microbial communities, and Δ12CH2D2 values are a key tracer of microbial recycling.en_US
dc.format.extent235 - 264en_US
dc.relation.ispartofGeochimica et Cosmochimica Actaen_US
dc.rightsAuthor's manuscripten_US
dc.titleThe Relative Abundances of Resolved 12CH2D2 and 13CH3D and Mechanisms Controlling Isotopic Bond Ordering in Abiotic and Biotic Methane Gasesen_US
dc.typeJournal Articleen_US

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