ACTIVELY SERPENTINIZING SEEPS IN THE BAY OF ISLANDS OPHIOLITE, WESTERN NEWFOUNDLAND: A WINDOW INTO THE DEEP BIOSPHERE

Uplifted oceanic lithosphere exposed at Earth’s surface at the Bay of Islands Ophiolite (˜485 Ma, as in Kurth et al., 1998) in Gros Morne National Park, Newfoundland, Canada is experiencing active serpentinization, a geologic process that may generate a habitable subsurface due to associated production of hydrogen and methane. A subsurface biosphere driven by the reducing power of abiotically produced hydrogen is of high interest both to terrestrial biogeochemistry and astrobiology, since the olivine-rich, ultramafic parent rocks requisite for serpentinization are common to Earth and other silicate planets, such as Mars.

We report results of a field survey documenting that fluid seeps, where deeply sourced fluids escape the evolving ultramafic subsurface to a heavily serpentinized surface environment, occur along the serpentine talus slope of the Tablelands, near Shoal Brook. Seep fluids bear elevated Ca/Mg ratios (Roberts and Deering, 2005), extremely important for the vegetative process in areas with serpentinized rocks, driven by high concentrations of aqueous Ca, an element not well accommodated in serpentine minerals. At these seeps, we also observe elevated pH (>11) at 25°C, with stripped gas contents of 60 ml samples up to ˜500 ppm H₂ and 6-8 ppm CH₄. Seep waters also contain ˜0.5 ppm nitrate, ˜0.005 ppm nitrite, ˜0.045 ppm NH₃, ˜1 ppm sulfate, ˜1 ppm aqueous silica, and diverse trace metals, with active carbonate deposition at fluid outlets. These well developed travertine aprons serve as testament to the interaction of serpentinizing fluids with our planetary atmosphere: seep waters that are high in calcium and low in carbonate react with our CO₂-rich atmosphere to produce CaCO₃ mineralization, visible from a distance overland. We report new data on fluid geochemistry, gas contents, associated serpentine mineralogy, quantitative PCR, and thermodynamic calculations to describe metabolic opportunities available to a putative subsurface biosphere.