Abstract
Oceanic crust is a vast and hydrologically active potential habitat for microbial life, with large areas of oceanic crust exposed at the seafloor that serve as conduits of exchange for fluids, heat, solutes, and biological materials between the ocean and the lithosphere. Circulating fluids are not in thermodynamic equilibrium with chemically reduced basaltic crust, resulting in redox reactions that could support growth of microbes. However, the existence and functioning of a deep biosphere within exposed and deep oceanic crust is largely unknown and unconstrained.

We have been using novel microbial colonization experiments deployed within igneous ocean crust on the eastern flank of the Juan de Fuca Ridge, to examine crustal microbial communities in situ within young (3.5 Ma) oceanic crust. Polished rock chips have been used as colonization surfaces, and borehole fluids were collected using OsmoSamplers deployed directly below the microbial observatories, and temperature loggers were also deployed in tandem as well. Molecular biology, mineralogy, chemistry, microscopy, and thermodynamic modeling will be presented to describe these experiments.

Image at right: Twisted mineral stalks produced by iron oxidizing bacteria recovered from mineral incubation experiments in Juan de Fuca boreholes.