HR: 11:50h
AN: B52A-07    [Abstracts]
TI: Supply and Demand in Subseafloor Basalt Aquifers
AU: * Shock, E L
EM: eshock@asu.edu
AF: School of Earth & Space Exploration, Arizona State University, Tempe, AZ 85287, United States
AU: * Shock, E L
EM: eshock@asu.edu
AF: Department of Chemistry & Biochemistry, Arizona State University, Tempe, AZ 85287, United States
AB: Subseafloor basalt aquifers contain 26 million cubic kilometers of water populated by unknown microbes that mediate the fluxes of elements between ridge flanks and seawater. The energy supporting this deep biosphere originates in the fundamental disequilibria between mid-ocean ridge basalts and seawater. Quantifying energy supplies depends in part on sampling and analysis of basalt aquifer fluids and in part on theoretical models of energy flow in complex natural systems. These approaches are joined through affinity diagrams that provide quantitative frameworks for testing models of the feedback between metabolism and weathering of oceanic crust. Fluid compositions can result from conductive cooling of hydrothermal fluids or mixing of hydrothermal fluids and seawater in regions proximal to the ridge, and conductive warming of seawater in basalt aquifers distal from the ridge. In all cases, temperature changes can be accompanied by diverse fluid-rock reactions. As a consequence, fluids can reach similar temperatures through multiple geochemical pathways, leading to diverse compositions. It is expected that these differences engender different habitats. Those influenced by deep hydrothermal fluids, such as post-eruptive fluids sampled at ridges and seamounts of the northeast Pacific, tend to be somewhat more acidic than habitats influenced by conductive heating of seawater. New results indicate that even at relatively low temperatures, these fluids provide ample energy for biosynthetic pathways including lipid and amino acid synthesis. For conductively heated habitats, preliminary results indicate that nitrate reduction must be coupled to oxidation of iron-bearing silicates for overall affinities to decrease in response to metabolism. In the extreme case of restricted fluids, in which water is the oxidant, hydrolytic oxidation of olivine provides sufficient hydrogen to reduce nicotineamide adenine dinucleotide at prevailing pH and silica activities. These are examples of how coupling biochemical demands with geochemical energy supplies defines habitats as alteration products and permits the integration of metabolism into assessments of elemental cycles.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0448 Geomicrobiology
DE: 0450 Hydrothermal systems (1034, 3017, 3616, 4832, 8135, 8424)
DE: 0463 Microbe/mineral interactions
SC: Biogeosciences [B]
MN: 2007 Fall Meeting