HR: 1340h
AN: OS33A-1454    [Abstracts]
TI: Bio-mediated Fe-deposits Associated With a Newly Discovered Vent Field at the Mohns Ridge
AU: * Thorseth, I H
EM: Ingunn.Thorseth@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, N-5007 Norway
AU: Pedersen, R B
EM: Rolf.Pedersen@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, N-5007 Norway
AU: Kruber, C
EM: Claudia.Kruber@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, N-5007 Norway
AU: Kosler, J
EM: Jan.Kosler@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, N-5007 Norway
AU: Steinsbu, B O
EM: Bjorn.Steinsbu@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, N-5007 Norway
AU: Johannessen, T
OS33A-1454 AF: Department of Biology, University of Bergen, Jahnebakken 5, N-5020, Bergen Norway
AU: Ovreaas, L
EM: Lise.Ovreas@bio.uib.no
AF: Department of Biology, University of Bergen, Jahnebakken 5, N-5020, Bergen Norway
AB: Textural, mineralogical and chemical features of rust colored mounds and chimney-like structures of the newly discovered hydrothermal vent field at the Mohns Ridge have been investigated to clarify the genesis of the deposits. The deposited material has a highly porous microtexture of branching, twisted filaments resembling stalks of the iron-oxidising Gallionella sp, but other unidentified filamentous structures are also present. The material is loosely consolidated by thin lamina where the interspaces between the filaments are filled with granular to compact precipitates. The filaments and the compact interstitial material have a similar composition of mainly FeO and less SiO2, and electron diffraction reveal 2-line ferrihydrite. Fine-grained particles between filaments show in addition Mn-enrichment. The REE composition of the siliceous ferrihydrite deposits show a similar pattern to that of the basaltic crust, indicating that they formed from low-temperature hydrothermal fluids, derived from interactions between the basaltic crust and circulating seawater. The deposits are situated on hyaloclastite, which is cemented by silica and minor amounts (~1 vol%) of pyrite. The iron isotope ratios of individual sulphide crystals in the hyaloclastite vary between zero-slightly positive. The ferrihydrite deposits have an organic carbon content of 0.5 wt% with a delta 13C value of -21 ‰ and negative iron isotope ratios (delta 56Fe of -1.66 ‰ and delta 57Fe of -2.73 ‰), indicating bio-mediated filament formation and microbial fractionation of carbon and iron isotopes. This suggests colonization and growth of the iron oxidising bacterium Gallionella at the interface between the reduced vent fluid and the surrounding oxidized seawater, and successive nucleation and precipitation of ferrihydrite and amorphous silica on the microbial stalks, resulting in the formation of the mounds and chimneys. Results from ongoing molecular analyses and culturing may reveal if other chemolithotropic microorganisms are also present.
DE: 0448 Geomicrobiology
DE: 0450 Hydrothermal systems (1034, 3017, 3616, 4832, 8135, 8424)
DE: 0471 Oxidation/reduction reactions (4851)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005