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 origin this uncertain. To assess serpentinite aquifers within Samail Ophiolite, Oman, we determined fluid chemical compositions, analyzed taxonomic profiles fluid-hosted microbial communities, and measured isotopic compositions hydrocarbon gases. We found 16S rRNA gene sequences affiliated with methanogens were widespread aquifer. clumped isotopologue (D ) relative abundances less than equilibrium, consistent substantial production. Furthermore, observed an inverse relationship between dissolved inorganic concentrations across bearing microbiological evidence methanogenic activity, suggesting apparent isotope effect methanogenesis modulated by availability. An additional source evidenced presence -bearing inclusions Ophiolite our measurement high values ethane propane, which are similar to those reported studies -rich rocks from oceanic lithosphere. addition, aerobic methanotrophs and, lower abundance, anaerobic methanotrophs, indicating consumption ophiolite may further enrich 13C. conclude produced under varying degrees limitation mixes abiotic released inclusions. This study lends insight into functioning ecosystems supported water/rock reactions.