HR: 1340h
AN: B13A-0171    [Abstracts]
TI: Phylogenetic Diversity of Young Ocean Crust at the East Pacific Rise 9$\deg$N
AU: * Santelli, C M
EM: csantelli@whoi.edu
AF: MIT/WHOI Joint Program in Oceanography, 360 Woods Hole Rd., Woods Hole, MA 02543
AU: Bach, W
EM: wbach@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Rd., Woods Hole, MA 02543
AU: Rogers, D R
EM: drogers@whoi.edu
AF: MIT/WHOI Joint Program in Oceanography, 360 Woods Hole Rd., Woods Hole, MA 02543
AU: Edwards, K J
EM: katrina@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Rd., Woods Hole, MA 02543
AB: Numerous studies show increasing evidence for a significant biosphere in oceanic lithosphere. Geochemical modeling suggests that most biological activity at or below the seafloor occurs in young crust ($<$10 Ma) on mid-ocean ridge flanks where low-temperature fluid circulation is substantial. In this environment, oxygenated seawater reacts with basalt and releases chemical energy that could support the growth of microorganisms. Fluid fluxes rapidly decrease further off-axis in older, more altered crust likely leading to a sharp decline in biological activity. To date, most evidence in support of a deep biosphere relies on anomalous textural features and geochemical signatures in aged basalt glass. In order to unambiguously attribute these alteration features to microbial activity, molecular microbiological data is required to corroborate these morphological and chemical observations. The application of molecular techniques to old ocean crust, however, can be difficult because of issues such as low cell density, contamination, and sluggish activity. Hence, studies on young ocean crust may provide insight and constraints on processes that could also apply to older crust. In this study, we have investigated the initial colonization of very young mid-ocean ridge basalt by endolithic microorganisms, and the changes in microbial diversity as a result of increasing rock alteration. Seafloor basalt samples were collected during RV {\it Atlantis} cruise AT11-7 in February 2004, from the East Pacific Rise (EPR) between 9$\deg$28'N and 9$\deg$50'N. Samples representing various flow morphologies, glass contents, and ages (up to $\sim$20 kyrs) were collected by DSV {\it Alvin} and brought to the surface in bioboxes. All basalts contain glass that ranges from very fresh to slightly altered with Fe-oxidation rims and/or Mn-oxide crusts. Total community DNA was successfully extracted from glass samples representative of a variety of alteration states. Clone libraries were constructed from PCR products of 16S rRNA genes using bacterial primers. Approximately 90 randomly selected clones from each library were sequenced. Phylogenetic analyses will indicate the overall diversity of young ocean crust and will help determine the succession of microorganisms colonizing the rock with increasing alteration. These results may also give us a better indication of the physiology of these microorganisms. Ultimately, this information will provide more accurate estimates of the impact of microbial activity in important geochemical processes such as the evolution of crustal composition.
DE: 4815 Ecosystems, structure and dynamics
DE: 4840 Microbiology
DE: 4885 Weathering
DE: 1050 Marine geochemistry (4835, 4850)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting