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Project Progress

The primary focus of this project over the last year has been investigation of the amounts and types of chemical energy available to support chemosynthetic microbial communities in ultramafic-hosted submarine hydrothermal systems. Chemosynthetic microbial communities in these systems utilize dissolved hydrogen and methane produced by the reaction of heated seawater with the underlying ultramafic rock as energy sources. Geochemical models indicate that the total amount of chemical energy potential available for microbial metabolism in these ultramafic systems is comparable to, or greater than, that available in the better-studied basalt-hosted systems, although the dominant forms of chemical energy are substantially different (i.e., hydrogen- and methane-oxidation rather than sulfide oxidiation). Since hydrogen is the main driver for metabolic energy for chemosynthesis in these systems, additional models were conducted to investigate the fluid-rock interactions responsible for hydrogen generation (i.e., serpentinization). Results of these models indicate that temperature and the partitioning of iron among alteration minerals exert the dominant controls on the amount of hydrogen produced, with hydrogen production peaking during hydrothermal alteration at temperatures around 300C and falling off steeply at both higher and lower temperatures. This result suggests that the most productive microbial communities should occur in hydrothermal systems with temperatures around 300C, although seafloor systems in this temperature range have so far gone undiscovered.