HR: 14:40h
AN: B42C-05 INVITED     [PDF]
TI: Controls on Sub-seafloor Bioalteration of Mid-Ocean Ridge Basalt Glass
AU: * Muehlenbachs, K
EM: karlis.muehlenbachs@ualberta.ca
AF: University of Alberta, Dept. of Earth and Atmospheric Sciences, Edmonton, AB T6G 2E3 Canada
AU: Furnes, H
EM: harald.furnes@geo.uib.no
AF: University of Bergen, Department of Earth Sciences, Bergen, 5007 Norway
AU: Banerjee, N R
EM: banerjee@ualberta.ca
AF: University of Bergen, Department of Earth Sciences, Bergen, 5007 Norway
AU: Staudigel, H
EM: hstaudigel@ucsd.edu
AF: Scripps Institution of Oceanography, Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, 8800 Biological Grade, LaJolla, CA 92037 United States
AB: Microbiological alteration of MORB glass has been documented in all the ocean basins by at least 4 research groups. It is readily recognized optically as tubular textures of micron-scale, channel-like features and branching bodies extending from palagonite alteration rims into fresh glass, or granular textures which are irregular patches of individual or coalesced spherical bodies protruding into fresh glass. SEM imaging of these features commonly reveals delicate filament-like structures, and material resembling desiccated biofilm. Bioalteration appears to be most pronounced several hundred meters beneath the seafloor at ambient temperature near 70 C and seems to follow rock permeability. The densest bioalteration reported so far has been of a submarine tuff. Bioalteration has been reported in the oldest ODP Holes and perhaps continues as long as glass persists and pore water flows. X-ray element maps show elevated levels of C, N, P, and K associated with suspected microbial alteration fronts. Rarely, sulfide grains are seen with the bio-features. Staining indicates that both Bacteria and Archea are active. Carbon isotope signatures in MORB glass show differences from those of the adjacent crystalline cores that likely relate to microbial activity during alteration. The generally low 13-C ratios of disseminated carbonates in basaltic glass are attributed to metabolic byproducts of Bacteria formed by oxidation of dissolved organic matter from pore waters. A few positive 13-C values have been observed. These come from slow-spreading ridges and suggest in those settings lithotrophic utilization of CO2 in which methanogenic Archaea produced CH4. No convincing explanations have been put forward on why or how microbes attack glass underneath the seafloor. However, this sub-seafloor ecological niche may have been exploited by microbes since the Proterozoic or even the Archean based on preliminary studies on ancient ophiolites.
DE: 1635 Oceans (4203)
DE: 1749 Volcanology, geochemistry, and petrology
DE: 4815 Ecosystems, structure and dynamics
DE: 4885 Weathering
DE: 8125 Evolution of the Earth
SC: Biogeosciences [B]
MN: 2003 Fall Meeting