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Title: Geochemical, Biological, and Clumped Isotopologue Evidence for Substantial Microbial Methane Production Under Carbon Limitation in Serpentinites of the Samail Ophiolite, Oman

In hyperalkaline () fluids that have participated in low‐temperature (<150) serpentinization reactions, the dominant form of C is often methane (), but the origin of thisis uncertain. To assessorigin in serpentinite aquifers within the Samail Ophiolite, Oman, we determined fluid chemical compositions, analyzed taxonomic profiles of fluid‐hosted microbial communities, and measured isotopic compositions of hydrocarbon gases. We found that 16S rRNA gene sequences affiliated with methanogens were widespread in the aquifer. We measured clumped isotopologue (D and) relative abundances less than equilibrium, consistent with substantial microbialproduction. Furthermore, we observed an inverse relationship between dissolved inorganic C concentrations andacross fluids bearing microbiological evidence of methanogenic activity, suggesting that the apparent C isotope effect of microbial methanogenesis is modulated by C availability. An additional source ofis evidenced by the presence of‐bearing fluid inclusions in the Samail Ophiolite and our measurement of highvalues of ethane and propane, which are similar to those reported in studies of‐rich inclusions in rocks from the oceanic lithosphere. In addition, we observed 16S rRNA gene sequences affiliated with aerobic methanotrophs and, in lower abundance, anaerobic methanotrophs, indicating that microbial consumption ofin the ophiolite may further enrichin13C. We conclude that substantial microbialis produced under varying degrees of C limitation and mixes with abioticreleased from fluid inclusions. This study lends insight into the functioning of microbial ecosystems supported by water/rock reactions.

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Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Journal of Geophysical Research: Biogeosciences
Medium: X
Sponsoring Org:
National Science Foundation
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