HR: 1340h
AN: OS23A-1042    [Abstracts]
TI: Physical and bio-chemical mass-balance model around seafloor cold seepages
AU: * Yamazaki, T
EM: tetsuo-yamazaki@aist.go.jp
AF: Natl. Inst. of AIST, 16-1 Onogawa, Tsukuba, 305-8569, Japan
AU: Takeuchi, R
EM: lika@eps.s.u-tokyo.ac.jp
AF: Univ. of Tokyo, 7-3-1 Hongo, Bunkyou-ku, Tokyo, 113-0033, Japan
AU: Monoe, D
EM: Monoe.Daisuke@cti.co.jp
AF: Chuden CTI Co., Ltd., Nihonseimei-Sasashima Bldg., 1-27-2 Meieki-Minami, Nakamura- ku, Nagoya, 450-0003, Japan
AU: Oomi, T
EM: Oomi.Tomoaki@cti.co.jp
AF: Chuden CTI Co., Ltd., Nihonseimei-Sasashima Bldg., 1-27-2 Meieki-Minami, Nakamura- ku, Nagoya, 450-0003, Japan
AU: Nakata, K
EM: nakata@scc.u-tokai.ac.jp
AF: Tokai Univ., 3-20-1 Orido, Shimizu-ku, Shizuoka, 424-8610,
AU: Fukushima, T
EM: t-fukushima@sof.or.jp
AF: Ocean Policy Research Foundation, Kaiyo Senpaku Bldg., 1-15-16 Toranomon, Minato-ku, Shizuoka, 105-0001, Japan
AB: Natural cold seepages are characterized as rapid upward transports of methane from deeper part of geological structures to the seafloors. Prior to reach the seafloors, when methane meets downwards diffusing seawater sulfate, it is oxidized anaerobically by a consortium of microorganisms that use sulfate as an oxidant, producing sulfide. The anaerobic oxidation of methane and anaerobic sulfate reduction are clarified as a coupled biological activity. A significant portion of the bicarbonate produced after the sulfate reduction as authigenic carbonate, mainly aragonite and high-Mg calcite, near the seafloor. Where the methane fluxes are much, these anaerobic reactions occur just beneath the seafloor. There, usually sulfur oxidizing microorganisms are visible on the seafloor just above the coupled consortium of microorganisms. They are called bacterial mats. When the fluxes too much, direct methane bubbling occurs and chemosynthesis-immobilization communities such as tubeworms and clams distribute around the bubbling locations with the bacterial mats. The physical and bio-chemical mass-balance model around cold seepages on seafloor and in water column has been studied by the authors and some preliminary results were reported (Yamazaki et al., 2005 and 2006; Takeuchi et al., 2007). The approach is to analyze the existing field observation and numerical modeling studies of cold seepages and to create a new physical and bio-chemical mass-balance model in the environment. The model is separated into three parts. They are methane supply, seafloor ecosystem, and water column units. The seafloor ecosystem unit has been improved to analyze the unsteady formation processes of the ecosystem. The time dependencies of formations of the consortium of microorganisms (AOM), the chemosynthetic community, and bicarbonates examined with the improved model are introduced. After the bubbling from seafloor, the methane bubble jet blows up in the water column due to the buoyancy. Then the dissolution and dispersion process of the methane plume with the oxidation occurs in the water column. These are the functions included in the water column unit. Because no systematic observation of methane plume behavior was found in literatures, a combined field observation with ADCP mooring and CTD-casting with seawater sampling was conducted during the R/V Tansei-maru cruise KT-06-26 at the Umitaka Spur off Joetsu region, eastern Japan Sea. Applying the simultaneous measurement data of methane concentration distribution and current profile in the water column obtained from the field observation into the water column unit, the methane flux bubbling into the water column was estimated. The result is also introduced. When we use the natural methane hydrates in deep-ocean as energy resources, the reactions of ecosystem around the exploitation sites must be assessed in advance. Unsteady and short term solutions and expectations are necessary in the assessment.
DE: 4255 Numerical modeling (0545, 0560)
DE: 4811 Chemosynthesis
DE: 4815 Ecosystems, structure, dynamics, and modeling (0439)
DE: 4851 Oxidation/reduction reactions (0471)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting