HR: 1330h
AN: B12A-0732    [PDF]
TI: Geomicrobiology of Archaeal Communities Isolated from an Off-axis Abyssal Hill Fault Scarp on the East Pacific Rise Flank at $9\deg$ 27'N
AU: * Ehrhardt, C J
EM: cehrhardt@umail.ucsb.edu
AF: Department of Geological Sciences, UC-Santa Barbara, Santa Barbara, CA 94106 United States
AU: Haymon, R
EM: haymon@geol.ucsb.edu
AF: Department of Geological Sciences, UC-Santa Barbara, Santa Barbara, CA 94106 United States
AU: Holden, P
EM: holden@bren.ucsb.edu
AF: Donald Bren School of Environmental Science and Management, UC-Santa Barbara, Santa Barbara, CA 93106 United States
AU: Lamontagne, M
EM: lamontag@bren.ucsb.edu
AF: Donald Bren School of Environmental Science and Management, UC-Santa Barbara, Santa Barbara, CA 93106 United States
AB: Although heat flow studies suggest that ~70% of the hydrothermal heat loss in the oceans occurs in the abyssal hill terrain on the flanks of mid-ocean ridges, very few off-axis hydrothermal sites have been discovered. In May 2002, sedimentary blowout structures of probable hydrothermal origin were discovered along East Pacific Rise at $9\deg$ 27'N on an off-axis abyssal hill bounded by a fault scarp covered with orange-brown microbial flocculations. Recovered samples of these flocculations have presented an opportunity to study the unknown nature and role of thermophilic and hyperthermophilic microbial communities on the ridge flanks. Furthermore, the archaeal communities that we have identified in the samples are useful "microbial tracers" which can be used to locate off-axis areas of moderate-to-high temperature fluid flow ($>$$50\deg$C). In this study, we used molecular techniques to isolate, amplify, and sequence community archaeal RNA sequences from fault scarp flocculations collected with a slurp pump system mounted in the Alvin basket. Molecular phylogenies based on 16S rRNA were constructed. Phylogenetic relationships of isolated clones were used to infer temperature preferences of archaeal communities. We identified 12 clones that clustered within thermophilic or hyperthermophilic clades within Archaea suggesting that moderately high temperature fluid ($>$$50\deg$C) exited the seafloor along this abyssal hill fault scarp. Our studies also suggest that these communities mediate the formation of Fe-sulfide mineral phases. Analysis of the samples with an Environmental Scanning Electron Microscope (ESEM) and X-ray energy dispersive analysis (EDS) revealed unique iron sulfide mineral phases with anomalously low Fe/S ratios in direct association with microbial communities.
DE: 0400 Biogeosciences
DE: 4832 Hydrothermal systems
DE: 4840 Microbiology
SC: Biogeosciences [B]
MN: 2003 Fall Meeting