Accessing the subsurface biosphere within rocks undergoing active low-temperature serpentinization in the Samail ophiolite (Oman Drilling Project) Journal Article uri icon

Overview

abstract

  • ; The Oman Drilling Project established an “Active Alteration”; multi-borehole observatory in dunite and harzburgite undergoing; low-temperature serpentinization in the Samail ophiolite. The highly; serpentinized rocks are in contact with strongly reducing fluids.; Distinct hydrological regimes, governed by differences in rock porosity; and fracture density, give rise to steep redox (Eh +200 to -750 mV) and; pH (pH range 8.5 to 11.2) gradients within the 300 to 400 meter deep; boreholes. The serpentinites and fluids host an active subsurface; ecosystem. Microbial cell abundances vary at least 6 orders of; magnitude, from ≤3.5*10; 1; cells/g to; 2.9*10; 7; cells/gram. Low levels of biological sulfate; reduction (2-1000 fmol/cm; 3; /day) can be detected in; rock cores, particularly in rocks in contact with reduced groundwaters; with pH <10.5.; Thermodesulfovibrio; is the predominant; sulfate reducer identified via metagenomic sequencing of adjacent; groundwater communities. We infer that transport and reaction of; microbially generated sulfide with the serpentine and brucite; assemblages gives rise to optical darkening and sulfide overprinting,; including the formation of tochilinite-vallerite group minerals,; potentially serving as an indicator that this system is inhabited by; microbial life. Olivine mesh-cores replaced with ferroan brucite and; minor awaruite, abundant veins containing hydroandradite garnet and; polyhedral serpentine, and late-stage carbonate veins are suggested as; targets for future spatially-resolved life-detection investigations. The; high-quality whole-round core samples that have been preserved can be; further probed to define how life distributes itself and functions; within a system where chemical disequilibria are sustained by; low-temperature water/rock interaction, and how biosignatures of; in-situ; microbial activity are generated.;

publication date

  • March 4, 2021

has restriction

  • hybrid

Date in CU Experts

  • March 19, 2021 9:26 AM

Full Author List

  • Templeton AS; Ellison ET; Glombitza C; Morono Y; Rempfert KR; Hoehler T; Zeigler SD; Kraus E; Spear J; Nothaft D

author count

  • 18

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