Subseafloor Ocean Crust Microbial Observatories: Development of FLOCS (FLow-through Osmo Colonization System) and Evaluation of Borehole Construction Materials

Abstract

Although oceanic crust is the largest contiguous, hydrologically active environment on Earth, very little is empirically known about crustal habitability due to obstacles faced in scientific sampling, especially in basaltic crust. Geologically young, chemically reduced basaltic crust is not in thermodynamic equilibrium with seawater or hydrothermal fluids; exploitation of the inherent thermodynamic disequilibrium may fuel microbial ecosystems in subsurface environments. One avenue to explore the basaltic deep biosphere is through the deployment of microbial observatories at seafloor exposures and inside boreholes drilled into the crust. We report the design and field-testing of flow-through microbial observatories for use in deep biosphere studies conducted in boreholes within oceanic crust. We also evaluate the suitability of borehole construction materials in order to inform the development of the next generation of observatories for microbial studies, with attention towards minimizing in situ leaching of (potentially) growth-inducing substrates (i.e., carbon, nitrogen, iron).

Keywords:

• biogeochemical cycling
• biomineralization
• deep biosphere
• iron oxidation
• molecular ecology

We thank K. Hunter and S.B. Joye for providing DOC and TDN concentration data, H. Jannasch for consultation on FLOCS design, D. Wiggins and M. Cowan of the University of Southern California CLAS Machine Shop for fabricating FLOCS parts, A. Fisher for providing access to Juan de Fuca CORKs for deployments, G. Horn for assistance in assembling FLOCS for deployment at Loihi, B. Toner for assistance in sampling Loihi FLOCS, O. Johnson and K. Petersen for sharing design information that assisted in the design of the rock slide chamber, B. Glazer for in situ temperature profiling, F. Corsetti for providing access to rock saw equipment, T. Pettigrew for providing materials for leaching experiments, S. Shanker for DNA sequencing, pilots and support crew of ROV Jason and DSV ALVIN for superb submarine operations, the captains and crews of R/V Thompson and R/V Atlantis for excellent at-sea operations, and the North Pond CORK working group for feedback on the FLOCS design and leaching experiments. This work was supported by funding from the NSF Ocean Drilling Program (OCE-0737300 to KJE), the NSF Microbial Observatories “FeMO” Program (MCB-0348425 to KJE), and the Gordon and Betty Moore Foundation (#1609 to KJE and GW). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of these agencies.