A Geochemical Comparison of Three Terrestrial Sites of Serpentinization: The Tablelands, the Cedars, and Aqua de Ney

Abstract

AbstractAlthough the Earth's subsurface hosts an abundance of microbial life, the influence of geochemistry on these communities remains poorly constrained. Ophiolites, sites where oceanic ultramafic minerals can be hydrated to serpentine minerals and metal oxides, create unique conditions capable of sustaining life. The fluid geochemistry of the Tablelands (NL, CAN), The Cedars (CA, USA), and Aqua de Ney (CA, USA), were studied to better characterize the range of fluid compositions observed at terrestrial sites of serpentinization. Fluids from these sites shared many commonalities including being ultra‐basic and reducing as well as having elevated levels of Cl−, Na+, K+, and Br− and depleted concentrations of Mg2+. They also exhibited a wide range of geochemistry. Isotopic and compositional data suggested the CH4 from The Cedars was a mixture of microbial and non‐microbial sources while the CH4 from the Tablelands was non‐microbial in origin. Aqua de Ney was the only site where the CH4 plotted in the abiogenic field. Despite being a known product of serpentinization, no H2 was detected at Aqua de Ney, likely due to the formation of abiogenic CH4 as well as the reaction of H2 and SO42− in the system to produce H2S. These unique sites of terrestrial serpentinization help to better understand the range of geochemistry at sites of serpentinization and its influence on the microbial communities in the subsurface.