9729672 Giovannoni This research suggests a program to test the hypothesis that there is a substantial microbial biosphere living within the oceanic upper crustal rocks of the off-axis ridge flanks, hundreds of meters below the water-rock interface, by detecting specific metabolic products which are associated with these sub-surface microbial communities. These diagnostic organic compounds should accompany the hydrothermal fluid that is known to circulate within the upper crustal rocks and eventually discharges into the overlying seawater at diffuse vent sites in exposed rock outcrops. We will also detect and phylogeneticallv characterize (ribosomal RNA molecular probe) any cellular biomass associated with fluid discharges. To test the ridge flank subsurface biosphere hypothesis, we propose to build an instrumented "bio-blanket" that focuses up-welling fluid emanating from these diffuse vent areas through relatively small scavenging columns that serve as traps for metabolic (organic carbon) products. The proposed instrumented blanket would also measure up-welling temperatures and velocities as the hydrothermal fluid vents into seawater. The development of the bio-blanket will be in several stages: initial instrument-component tests and fluid sampling will exploit the convenient valved- plumbing system of the "corked" ODP Hole 1026B, which has documented 65 C outflowing fluids; subsequent complete prototype instruments will be deployed over active diffuse vents at both an exposed outcrop at a ridge flank site (Baby Bare, Cascadia Basin) and a mid-ocean ridge spreading center (Endeavour Segment), where flux rates are high and the signal-to-noise ratio of any component of the fluid is quite large. The direct detection of a wide-spread biological community, living within the sub-surface ocean floor in the older ridge flank regions, would dramatically alter our estimates of biological productivity and the global carbon budgets, and have a profound impact on o ur philosophical view of the earth. ***
