HR: 0800h
AN: V51C-1507    [Abstracts]
TI: Preliminary Investigations Into the Geomicrobiology of Iron-Rich Seafloor Sediments Obtained From the Tonga Ridge
AU: * Langley, S
EM: rlang053@uottawa.ca
AF: University of Ottawa, Department of Earth Sciences 140 Louis Pasteur, Ottawa, ON K1N6N5 Canada
AU: Fortin, D
EM: dfortin@uottawa.ca
AF: University of Ottawa, Department of Earth Sciences 140 Louis Pasteur, Ottawa, ON K1N6N5 Canada
AU: Hannington, M
EM: mhanning@uottawa.ca
AF: University of Ottawa, Department of Earth Sciences 140 Louis Pasteur, Ottawa, ON K1N6N5 Canada
AU: Stoffers, P
EM: pst@gpi.uni-kiel.de
AF: Institute of Geosciences, University of Kiel Olshausenstr. 40, Kiel, 24118 Germany
AU: Schwarz-Schampera, U
EM: u.schwarz-schampera@bgr.de
AF: Bundesanstalt fur Geowissenschaften und Rohstoffe, Stilleweg 2 , Hannover, 30655 Germany
AU: Submersible Group, P
EM: pisces@lava.net
AF: Hawaii Undersea Research Laboratory, University of Hawaii 1000 Pope Road, Honolulu, HI 96822 United States
AB: Two samples (designated P5-636 and P5-637) of seafloor sediment were collected from a depth of 900m at Volcano 19 in the Tonga Arc, an area with diffuse active venting at temperatures ranging from 30 to 112 degrees Celsius. Another sample, P640, was collected from a depth of 399m at Volcano 18, an area with no active venting and a maximum sediment temperature of 13.8 degrees Celsius. Macroscopic observations at Volcano 19 indicated white filamentous microbial mats growing in close association with putative iron oxide and silica-rich sediments. Microbial-sediment assemblages formed vertical chimneys up to 2 metres tall which were easily disrupted and collapsed when disturbed. Scanning electron microscopy of sediments P5-636 and P5-637 revealed abundant microbial filaments, 1 to 2 micrometres wide and up to tens of micrometres long which were often, though not always, encrusted by mineral material. Bacilli and coccoid forms were also observed, but at a much lower frequency. Energy-dispersive X-ray spectroscopy (EDS) of non-encrusted cell surfaces revealed light elements commonly associated with biological material and/or saline evaporites (e.g., Na, K, Mg, Ca). EDS of the encrusting mineral phase resulted in large increases in signals for iron, silicon and oxygen. Morphologically, P5-636 and P5-637 were a mixture of amorphous spherical aggregates and abundant, well-defined, acicular and platy crystals measuring several micrometres in length. X-ray diffraction (XRD) analysis yielded several peaks corresponding to goethite and lepidocrocite, with perhaps some magnetite. This suggests that P5-636 and P5-637 are mixtures of goethite and/or lepidocrocite with a more amorphous phase (e.g., 2-line ferrihydrite). EDS analysis of P640 resulted in large signals for iron, oxygen and silicon. However, the mineral morphology of P640 sediment was largely that of amorphous spherical aggregates. The well-developed goethite/lepidocrocite crystals seen in P5-636 and P5-637 were markedly absent. XRD analyses of P640 sediments yielded only two broad reflections at 2.53 and 1.48 angstroms, suggesting that sediment P640 is composed primarily of 2-line ferrihydrite. Sediment P640 also showed a marked absence of the filamentous organisms seen in the other two samples. The few putative filaments which were observed were heavily encrusted and likely non-viable. Temperature differences between the two fields are an obvious factor in the differences in sediment mineralogy described here, since the higher temperatures recorded for P5-636 and P5-637 would tend to favour a more crystalline iron oxide. It remains to be determined, however, whether the same temperature difference might also account for the difference in microbial abundance seen between the two sediment fields. An intriguing alternative is that the microbes themselves may be exerting an additional (metabolic) control over the nature of the Tonga Arc sediments. Further investigation into the geomicrobiology of this site is clearly warranted. The authors gratefully acknowledge the work of the crew of Support Vessel R/V Ka'imikai-o-Kanaloa in collecting these samples.
DE: 0448 Geomicrobiology
DE: 0450 Hydrothermal systems (1034, 3017, 3616, 4832, 8135, 8424)
DE: 0463 Microbe/mineral interactions
DE: 3616 Hydrothermal systems (0450, 1034, 3017, 4832, 8135, 8424)
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005