Active microbial sulfate reduction in fluids of serpentinizing peridotites of the continental subsurface

Abstract Serpentinization of peridotites in Earth’s mantle is associated with the generation hydrogen and low molecular weight organics that could support subsurface life. Studies microbial metabolisms peridotite-hosted environments have focused primarily on methanogenesis, yet DNA sequences, isotopic composition sulfides thermodynamic calculations suggest there potential for sulfate reduction too. Here, we use a radiotracer-based method to quantify rates serpentinization fluids recovered from boreholes Samail Ophiolite, Oman California Coast Range USA. We find levels occur at pH up 12.3. These not be stimulated by addition hydrogen, methane or small organic acids, which indicates this metabolism limited factors other than substrate availability. Cellular activity drops > 10.5 suggests high fluid exerts strong control sulfate-reducing organisms peridotites.