subseafloor imageResearch

Subseafloor Biosphere

There is growing evidence that a substantial subseafloor biosphere may extend throughout the immense volume of aging, sediment-buried crust underlying the global system of mid-ocean ridge (MOR) flanks and ocean basins, but there is presently insufficient data to constrain theoretical thinking and identify actual microbial activity in situ. We work with a variety of collaborators to investigate the geochemical conditions and microbial communities of the deep subsurface, through utilization of Integrated Ocean Drilling Program CORK observatories. We have active programs at the Juan de Fuca Ridge flanks in the Pacific Ocean and at North Pond on the mid-Atlantic Ridge.

Continuous water-rock reactions and the balance between heat flux and increasing sediment cover result in a range of temperatures, chemical gradients, and redox disequilibria that affect globally significant heat loss and chemical flux to the overlying ocean, and may sustain a significant and complex microbial community. However, this potentially important subseafloor basement biosphere is virtually unexplored. Because water-rock reactions and associated microbial habitats vary with crustal temperature and age, our projects and collaborations work to compare geochemistry and microbial diversity in crustal fluids from multiple borehole observatories on the flanks of the Juan de Fuca Ridge, ranging in basement age (~1.24 to 3.5 my) and in basement temperature (~38° to ~65°C). By comparison, North Pond basement age is ~7-8 my, with much cooler temperatures (<25°C).

placeholderThe synergy between redox reactions and the organisms living in proximity to them demands an interdisciplinary approach to research, but few studies have attempted to combine geochemical and biological characterizations at similar resolutions using equally advanced techniques. In situ, real-time voltammetric analyses simultaneously measures key dissolved redox species; such measurements help to elucidate the metabolic climate of the basement fluids and guide experimental and culturing efforts. These geochemical and biological data also serve as input parameters for thermodynamic calculations of numerous potential metabolic reactions.

Support for our subsurface biosphere research has been provided by the National Science Foundation (MCB-0604014, OCE-1061827) and the Gordon and Betty Moore Foundation (#1609), as well as through various support of collaborators and the NSF Science and Technology Center for Dark Energy Biosphere Investigations.

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