Aqueous Geochemical and Microbial Variation Across Discrete Depth Intervals in a Peridotite Aquifer Assessed Using a Packer System in the Samail Ophiolite, Oman

The potential for molecular hydrogen () generated via serpentinization to fuel subsurface microbial ecosystems independent from photosynthesis has prompted biogeochemical investigations of serpentinization-influenced fluids. However, typically sample surface seeps or open-borehole pumping, which can mix chemically distinct waters different depths. Depth-indiscriminate sampling methods could thus hinder understanding the spatial controls on nutrient availability life. To resolve groundwaters in a low-temperature serpentinizing environment, we deployed packers (tools that seal against borehole walls during pumping) two -deep, peridotite-hosted wells Samail Ophiolite, Oman. Isolation and pumping discrete intervals as deep below ground level revealed multiple aquifers ranged pH 8 11. Chemical analyses 16S rRNA gene sequencing deep, highly reacted bearing up , methane sulfate an ecosystem dominated by Bacteria affiliated with class Thermodesulfovibrionia, group chemolithoheterotrophs supported oxidation coupled reduction. In shallower, oxidized groundwaters, aerobic denitrifying heterotrophs were relatively more abundant. High (up respectively) indicated oxidation, particularly evidence mixing waters. This study demonstrates power spatially resolving probe their geochemical conditions chemosynthetic communities. Such information will help improve predictions where activity fractured rock might occur, including beyond Earth.