Ride Integrated Studies at 9degN East Pacific Rise: Establishing a Role for Fe and S Microbial Metabolism in Ocean Crust Weathering

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This integrated field and laboratory studies is investigating the role of chemosynthetic microbial communities in ocean crust alteration and biomass production in the deep-sea. The studies are based on preliminary studies concerning the early stages of ocean crust weathering and fluid-rock interactions in the shallow sub-seafloor. The principal hypothesis tested in this project is that the activities of autotrophic Fe- and S-oxidizing prokaryotes play important roles in the initial colonization and weathering of ocean crust. This process results in: 1) the development of sharp redox gradients associated with the surface crustal rock (seafloor-exposed surfaces, or subseafloor surfaces exposed to circulating fluids along fractures), and 2) a flux of fresh organic C (Corg) to ridge flanks that may be used for respiration by endolithic heterotrophic (including Fe- and S-reducing) prokaryote communities. These communities likely play a role in the development of secondary alteration zones rich in reduced Fe and S mineral phases (pyrite, magnetite), but their role in promoting crustal weathering is not yet known, and is being investigated in this project. The research has four principal components: 1. Using culture-dependent and culture-independent methods, examining the phylogenetic and physiologic diversity of endolithic Fe and S microorganisms associated with the early stages of ocean crust weathering (field-based). 2. Using geochemical techniques (elemental and isotopic), examining the progressive weathering of ocean crust along weathering rinds; correlate finding with (1) (field-based). 3. Conducting field-incubation studies for 6 mo. to 1 yr. using a suite of pre-characterized natural crust material (basaltic glass, basalt, varying compositions). Analyze according to (1) and (2). 4. Conducting laboratory experiments using existing and anticipated new strains of Fe and S microorganisms exploring the kinetic relationships between crust alteration and biomass production, and to determine elemental portioning and speciation effects attributable to biology. The fieldwork is based on two cruises: one cruise to EPR scheduled for Spring 03 (OCE-9819261, Drs. Fornari, Tivey, and Schouten, PI.s), and a second cruise to return to the same region 6-12 mo. later. The first cruise initiated field incubation experiments and collected some preliminary samples along transects at 9degreeN on basalt flows, of ages from ~0-20,000 yrs. The purpose of the follow-up cruise is to collect the field incubation samples and to collect fresh environment samples in a controlled manner that insures biological integrity of the material.