HR: 0800h
AN: OS21A-1197    [Abstracts]
TI: Dissolved barium and authigenic barite above gas hydrates: Microbially mediated reactions at the Sea of Japan UT04 Ridge and Seep Area.
AU: * Snyder, G T
EM: gsnyder@rice.edu
AF: Earth Science Dept., MS126 Rice University P.O. Box 1892, Houston, TX 77251-1892 United States
AU: Matsumoto, R
EM: ryo@eps.s.u--tokyo.ac.jp
AF: Dept. Earth and Planetary Sci., Tokyo University Hongo 7--3--1, Bunkyo-ku, Tokyo, 113--0033 Japan
AU: Hiruta, A
EM: hiruta@eps.s.u--tokyo.ac.jp
AF: Dept. Earth and Planetary Sci., Tokyo University Hongo 7--3--1, Bunkyo-ku, Tokyo, 113--0033 Japan
AU: Komatsubara, J
EM: komatsubara@eps.s.u--toko.ac.jp
AF: Dept. Earth and Planetary Sci., Tokyo University Hongo 7--3--1, Bunkyo-ku, Tokyo, 113--0033 Japan
AU: Takeuchi, R
EM: lika@eps.s.u--tokyo.ac.jp
AF: Dept. Earth and Planetary Sci., Tokyo University Hongo 7--3--1, Bunkyo-ku, Tokyo, 113--0033 Japan
AU: Sunamura, M
EM: sunamura@eps.s.u--tokyo.ac.jp
AF: Dept. Earth and Planetary Sci., Tokyo University Hongo 7--3--1, Bunkyo-ku, Tokyo, 113--0033 Japan
AU: Ishida, Y
EM: yasushi@eps.s.u--tokyo.ac.jp
AF: Dept. Earth and Planetary Sci., Tokyo University Hongo 7--3--1, Bunkyo-ku, Tokyo, 113--0033 Japan
AU: Tomaru, H
EM: hitoshi@earth.rochester.edu
AF: Dept. Earth and Environmental Sci., University of Rochester, Rochester, NY 14627 United States
AU: Okuda, Y
EM: ojuda.gsj@aist.go.jp
AF: Inst. Geo--Resources and Environment, Natl. Inst. Adv. Ind. Sci. and Tech. Tsukuba, Ibaraki, 305--8567 Japan
AU: Aoyama, C
EM: aoyamac@dokken.co.jp
AF: Japan's Indep. Inst. for Comprehensive Res., Ishii Bldg. Shinbashi Minato--Ku, Tokyo, 105--0004 Japan
AU: Numamani, H
EM: hnuma@kaseigakuin.ac.jp
AF: Tokyo Kaseigakuin Univ., Aihara 2600 Machida, Tokyo, 194--0292 Japan
AU: Hiromatsu, M
EM: mhiromat@suruga--g.co.jp
AF: Nippon Kayo Corp., Chiyoda--ku, Tokyo, 114--0005 Japan
AU: Aoyama, D
EM: aoyamadaiki@hotmail.com
AF: Japan's Indep. Inst. for Comprehensive Res., Ishii Bldg. Shinbashi Minato--Ku, Tokyo, 105--0004 Japan
AU: Koike, Y
EM: capkoike@s.kaiyodai.ac.jp
AF: Tokyo Univ. Marine Sci. and Tech., Konan Minato--ku, Tokyo, 108--8477 Japan
AU: Takeda, S
EM: takeda@s.kaiyodai.ac.jp
AF: Tokyo Univ. Marine Sci. and Tech., Konan Minato--ku, Tokyo, 108--8477 Japan
AU: Dickens, G R
EM: jerry@rice.edu
AF: Earth Science Dept., MS126 Rice University P.O. Box 1892, Houston, TX 77251-1892 United States
AB: Only recently described, the UT04 Ridge and Seep Area is one of Japan's most significant gas hydrate systems. Bathymetric profiles reveal numerous pockmarks and more than 30 major seeps, each approximately 100m in diameter. We present both shipboard and land-based geochemical data from 15 piston cores recovered on a recent cruise to the Ridge and discuss the influence of microbial oxidation of methane on pore-fluid and sediment chemistry. Although evidence for bioturbation is apparent in many of the cores, the relatively smooth profiles of pore-fluid chemistry throughout the Ridge suggest that regional-scale diffusion plays a greater role in fluid transport within the upper 5 meters than bioturbation or bioirrigation. The sulfate-methane transition (SMT) in the coring sites ranges in depth from 2 meters to 4 meters below the sea floor, and is characterized by high H$_{2}$S concentrations and an inflection in alkalinity profiles. Barium concentrations above the SMT are generally less than 1 $\mu$M. Pore-fluid profiles indicate active barite dissolution just below the SMT, as a result of sulfate depletion in the surrounding pore fluids, and concentrations rapidly approach maximum values of 20-50 $\mu$M. Dissolved barium produced in this region presumably diffuses upward and is reprecipitated as barite. In the one core where massive hydrate was recovered, authigenic concretions were interdispersed among sediment and hydrates throughout the entire sample interval (2.5 m). In this particular core, dissolved barium concentrations were much lower than can be accounted for by pore fluid dilution caused by hydrate dissociation. Ongoing analyses of authigenic barite accumulation will indicate the duration of active gas venting along the Ridge.
DE: 4805 Biogeochemical cycles (1615)
DE: 4825 Geochemistry
DE: 4851 Oxidation/reduction reactions
DE: 4875 Trace elements
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting