Extending the deep biosphere through ocean drilling: Bioalteration of volcanic glass in the oceanic crust

Details Extending the deep biosphere through ocean drilling: Bioalteration of volcanic glass in the oceanic crust Extending the deep biosphere through ocean drilling: Bioalteration of volcanic glass in the oceanic crust

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.u11b0005b&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #U11B-0005

Other

0400 Biogeosciences, 3035 Midocean Ridge Processes, 4825 Geochemistry, 4870 Stable Isotopes

Scientific paper

Scientific ocean drilling through the Deep Sea Drilling Program (DSDP) and Ocean Drilling Program (ODP) has provided a window into the deep biosphere. Microbial communities have been identified within hydrothermal vent systems at ocean floor spreading centers, deep within oceanic sediments, and within glassy portions of the basaltic oceanic crust of varying age. Questions still remain regarding the utilized metabolic pathways, how long such microbial activity persists within the oceanic crust, and how well it may be preserved on Earth or other planets. Microbial alteration of basaltic glass from ODP/DSDP cores and ophiolites can be documented by petrographic and biogeochemical techniques. Microbial alteration is seen as either tubular or granular textures. Tubular textures are characterized by micron-scale channel-like features extending from palagonite alteration rims into fresh glass. Granular textures appear as irregular patches of spherical bodies protruding into fresh glass. Detailed SEM imaging of these features commonly reveals delicate filament-like structures and material resembling desiccated biofilm. X-ray element maps invariably show elevated levels of C, N, P, and K associated with suspected microbial alteration features. Comparison of glasses from different ODP/DSDP holes indicates that carbon isotope ratios of carbonates in samples of microbially altered volcanic glass are commonly depleted by as much as -20 per mil, except in samples from slow-spreading ridges where both elevated and depleted C-isotope ratios are observed. In general, the microbes appear to be living off of dissolved organic matter with some evidence of lithoautotrophy at slow-spreading ridges. Maximum microbial activity seems to occur at ˜70° C but is moderated by pore water flow. We have applied nucleic acid staining techniques to many samples and imaged them with epifluorescence and laser scanning confocal microscopy. This has produced exceptional images that provide high resolution spatial information on the presence of DNA/RNA associated with areas of suspected microbial alteration. The biogenic features in samples of varying ages may, therefore, be relatively recent and the microbes may be currently active. We suggest that volcanic glass in the upper oceanic crust may host a previously overlooked and still unquantified flourishing deep biosphere that contributes significantly to global geochemical fluxes. Since key constituents in Martian soil appear to be analogous to palagonite the techniques developed for tracing biosignals could be easily applied to returned samples from regions where liquid water and conditions suitable for life may have existed.

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