HR: 0800h
AN: B31A-0964    [Abstracts]
TI: Metabolic Potential of the Deep Subseafloor at Selected Convergent Margins
AU: * Cardace, D
EM: dcardace@wustl.edu
AF: Department of Earth and Planetary Sciences, Washington University, One Brookings Drive, Campus Box 1169, St. Louis, MO 63130 United States
AU: Amend, J P
EM: amend@levee.wustl.edu
AF: Department of Earth and Planetary Sciences, Washington University, One Brookings Drive, Campus Box 1169, St. Louis, MO 63130 United States
AU: Morris, J D
EM: jmorris@levee.wustl.edu
AF: Department of Earth and Planetary Sciences, Washington University, One Brookings Drive, Campus Box 1169, St. Louis, MO 63130 United States
AB: The cold subseafloor is an extreme environment in which microbial metabolism appears to operate slowly but persistently over space and time. At convergent margins, subseafloor microbial communities experience diffuse flow of aqueous fluids through sediment interstices and variable flow of deeply sourced, advecting fluids. When these fluids mix, geochemical disequilibria are established, and may serve as energy sources in microbial metabolism. This study contrasts the metabolic potential of four near trench sedimentary environments associated with the Costa Rica, Cascadia, Nankai, and Izu-Bonin-Marianas subduction zones, which span much of the global range of water depths (~ 2500 to ~ 5800 m) and thermal structure (heat flow at seafloor ~ 15 to ~ 140 mW/m²) outboard of subduction zones. Geochemical data (pH, NH₄⁺, Na⁺, K⁺, Fe²⁺, Ca²⁺, Mg²⁺, HCO₃^-, Cl^-, SO₄^2-, SiO₂ (aq), CH₄ (aq), H₂ (aq), PO₄^3-, HS^-, and CH₃COO^-) collected during Ocean Drilling Program Legs 146, 170, 185, 190, and 201 are used in Gibbs free energy minimization calculations to model the bioenergetic potential of key metabolic reactions. At the four sites, pH values are 7.3-8.2, alkalinity values are 1 to 24 mM, and sulfate values are 0 to 30 mM. Notable site-specific differences exist in NH₄⁺ (ranging two orders of magnitude in concentration) and salinity (with reported values up to 40 psu at Izu). The specific reactions considered are: (1) CO₂ driven methanogenesis, (2) acetate driven methanogenesis, (3) methanotrophy coupled to sulfate reduction, (4) acetate oxidation coupled to sulfate reduction, (5) acetate oxidation coupled with nitrate reduction, (6) acetate oxidation coupled with ferric iron reduction. The standard Gibbs free energies are combined with the in situ geochemical parameters to calculate overall Gibbs free energies in deep subseafloor environments. In all cases, ferric iron reduction coupled with acetate oxidation yields the greatest energy (~-1600 kJ/mol), followed by nitrate reduction coupled to acetate oxidation (~-776 kJ/mol), sulfate reduction with acetate and CO₂ driven methanogenesis at roughly equivalent energetic yields (~-376 kJ/mol), methanotrophy coupled to sulfate reduction (~-224 kJ/mol), and finally acetate driven methanogenesis (~-200 kJ/mol). These reactions represent possible microbial metabolic strategies in the deep subseafloor near convergent margin trenches.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0456 Life in extreme environments
DE: 0460 Marine systems (4800)
DE: 0471 Oxidation/reduction reactions (4851)
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
SC: Biogeosciences [B]
MN: Fall Meeting 2005