HR: 1340h
AN: OS33C-1485    [Abstracts]
TI: Distribution of Dissolved Hydrogen in Pore Water at Cold Seep Site
AU: * Toki, T
EM:
AF: Ocean Research Institute, The University of Tokyo, 1-15-1, Minamidai, Nakano-ku, Tokyo, 164-8639 Japan
AU: Maegawa, K
EM:
AF: Department of Earth and Planetary Science, Hokkaido University, N8W10, Kita-ku, Sapporo, 060-0810 Japan
AU: Tsunogai, U
EM:
AF: Department of Earth and Planetary Science, Hokkaido University, N8W10, Kita-ku, Sapporo, 060-0810 Japan
AU: Ashi, J
EM:
AF: Ocean Research Institute, The University of Tokyo, 1-15-1, Minamidai, Nakano-ku, Tokyo, 164-8639 Japan
AU: Kinoshita, M
EM:
AF: Japan Agency for Marine-Earth Science and Technology, 2-15, Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Gamo, T
EM:
AF: Ocean Research Institute, The University of Tokyo, 1-15-1, Minamidai, Nakano-ku, Tokyo, 164-8639 Japan
AB: White patches have been observed at the Oomine Ridge (33°7.32'N, 136°28.75'E) on the Nankai accretionary prism. During the KY04-11 cruise (2004. 9. 5 ~ 2004. 10. 2) of the R/V Kaiyo (JAMSTEC), a sediment sample was obtained with a piston corer from the seafloor at the Oomine Ridge. The recovered sediment was 268.5 cm long. Subsampled sediments for gas analysis were taken and were treated for the extraction of dissolved gas in the pore water. The gas samples were measured for CH₄, δ¹³C(CH₄), CO₂, δ¹³C(CO₂), and H₂. The other subsamples for pore water analysis were taken from the residual sediment in the corer. The retrieved pore water samples were analyzed for NH₄⁺, Cl^-, SO₄^2-, CH₄, δ¹³C(CH₄), CO₂, δ¹³C(CO₂), δ¹⁸O(H₂O), and δD(H₂O). Chloride concentrations and both isotopic signatures (δ¹⁸O and δD) of the pore water decreased with depth, suggesting that the pore water in this site was affected by seeping fluid characterized by Cl, δ¹⁸O, and δD-depleted. Sulfate concentrations rapidly decreased within 2 m, indicating that sulfate consumption occurred in the surface sediments and/or sulfate-free fluid flowing upward. Ammonium concentrations increased with depth even after sulfate was completely reduced, which indicates that there are processes of organic matter decomposition that are capable of producing ammonium after sulfate reduction is complete. Methane concentrations showed concave-upward depth profile and carbon isotopic compositions of methane were as low as _E0 ‰PDB, indicating that methane is derived from microbial production in sediments. We observed a significant H₂ peak reaching 500 μmol/kg at the deepest sample, which would be produced as an intermediate during processes of organic matter decomposition in oxide-free environments.
DE: 4802 Anoxic environments (0404, 1803, 4834, 4902)
DE: 4811 Chemosynthesis
DE: 4820 Gases
DE: 4851 Oxidation/reduction reactions (0471)
DE: 4870 Stable isotopes (0454, 1041)
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005