HR: 14:30h
AN: V43F-04    [Abstracts]
TI: Microbially Produced Enrichment of CO and N$_{2}$O in Hydrothermal Plumes
AU: * Tsunogai, U
EM: urumu@ep.sci.hokudai.ac.jp
AF: Graduate School of Science, Hokkaido Univ., N10W8, Kita-ku, Sapporo, 0600810 Japan
AU: Nakagawa, F
EM: fuminaka@ep.sci.hokudai.ac.jp
AF: Graduate School of Science, Hokkaido Univ., N10W8, Kita-ku, Sapporo, 0600810 Japan
AU: Konno, U
EM: utaro@ep.sci.hokudai.ac.jp
AF: Graduate School of Science, Hokkaido Univ., N10W8, Kita-ku, Sapporo, 0600810 Japan
AU: Maegawa, K
EM: maegawa@ep.sci.hokudai.ac.jp
AF: Graduate School of Science, Hokkaido Univ., N10W8, Kita-ku, Sapporo, 0600810 Japan
AU: Gamo, T
EM: gamo@ori.u-tokyo.ac.jp
AF: Graduate School of Science, Hokkaido Univ., N10W8, Kita-ku, Sapporo, 0600810 Japan
AU: Ishibashi, J
EM: ishi@geo.kyushu-u.ac.jp
AF: Faculty of Science, Kyushu Univ., 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 8128581 Japan
AB: Effluent hydrothermal plumes are enriched with some components (such as CH$_{4}$, Mn, $^{3}$He, etc.) from surrounding seawater, because of extreme enrichment of these components in seafloor venting hydrothermal fluids from seawater. In recent studies, however, we found enrichment with CO and/or N$_{2}$O in hydrothermal plumes, while hydrothermal fluids exhibit comparable concentrations with seawater for the components. The enrichment with CO and/or N$_{2}$O in a hydrothermal plume reflects in situ microbial activities that have been stimulated by some primary components that derived from hydrothermal fluids. We took effluent hydrothermal plume water samples in and around the water column of Suiyo seamount (ca. 1,380m depth and ca. 2km diameter), Izu-Bonin arc, to determine concentrations and stable carbon isotopic compositions of carbon monoxide (CO) and methane (CH$_{4}$) in the plume. We also sampled venting fluids using manned submersible Shinkai 2000 to compare the chemical composition and isotopic composition of CO and CH$_{4}$ with those in the hydrothermal plume. We detected strong CH$_{4}$ anomalies not only on the water columns within the caldera, but also on those at outsides of the caldera at the depth of ca. 1,100-1,150m, the sill depth of the caldera wall. Within the plume, we detected significant CO enrichment. The stable carbon isotopic compositions of CO in the plume, however, exhibit highly $^{13}$C-depleted values (-110 to -60 \permil PDB) compared with those in seafloor venting hydrothermal fluids (around -30 \permil PDB). Besides, the plume samples exhibit higher CO/CH$_{4}$ ratio along with the distance from the fluid venting site. We conclude that some microbial activities result in CO production within the hydrothermal plume. Partial decompositions of CH$_{3}$OH produced during microbial CH$_{4}$ oxidation might be a possible origin for the CO in hydrothermal plume. This CO enrichment in deep seawater can be a good tracer for seafloor hydrothermal activities, especially detecting plumes located on rather distant place from venting site. Besides, the secondary chemical anomalies can be a tracer for quantifying in situ microbial activities in hydrothermal plumes.
DE: 8424 Hydrothermal systems (8135)
DE: 4820 Gases
DE: 4840 Microbiology
DE: 4870 Stable isotopes
DE: 1050 Marine geochemistry (4835, 4850)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting