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

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

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.