KATRINA EDWARDS, University of Southern California
"Life on the rocks in the deep-sea"
Roughly seventy percent of the Earth’s sea floor is exposed or shallowly buried ocean crust, equating to nearly fifty percent of Earth’s solid surface area. Most of this rock is composed of volcanic extrusive basalt, a mafic rock rich in iron and magnesium. By volume, oceanic crust is also the most vast, contiguous, hydrologically active environment on Earth. Despite its relatively large size, very little is empirically known about the biodiversity of the ocean crust because of its remoteness and our lack of contextual understanding of the role it play in biogeochemisty. However, volcanic extrusive rock at the seafloor, being produced in magma chambers that are largely reducing, produce rocks that are out of equilibrium with seawater and hence, seawater-rock alteration reactions with the ocean crust balance many key elemental budgets. Taking advantage of the disequilibria, microbial life may be supported by - and potentially mediate - alteration reactions between seawater and rock. As a first step in evaluating the ocean crust microbial habitat, we examined microbial communities hosted by basalts exposed at the seafloor near hydrothermal vents. The basalts, comprised of a range of oxidation conditions and chemical compositions, support exceptionally diverse microbial communities. Based on the inferred chemical reactions occurring between the basalts and seawater, sufficient energy is available for chemolithoautotrophic-based ecosystems. Taking the next step, microbial observatories designed for deployment deep in ocean crust will address whether sub-seafloor ocean crust supports a deep biosphere.