HR: 09:00h
AN: OS21A-05    [Abstracts]
TI: Near Sea Floor Gas Hydrate Formation and Influence on Pore Water Chemistry and Authigenic Carbonate at the Formosa Ridge, South China Sea
AU: * Lin, S
EM: swlin@ntu.edu.tw
AF: National Taiwan University, no. 1, Sec. 4, Roosevelt Rd., Taipei, 106, Taiwan
AU: Machiyama, H
EM: bucci@jamstec.go.jp
AF: Kochi Inst. for Core Sample Research, Japan Agency for Marine-Earth Sci. & Tech., B200, Monobe, Nankoku, Kochi, 783-8502, Japan
AU: Chen, Y
EM: ygchen@ntu.edu.tw
AF: National Taiwan University, no. 1, Sec. 4, Roosevelt Rd., Taipei, 106, Taiwan
AU: Soh, W
EM: soh@jamstec.go.jp
AF: Kochi Inst. for Core Sample Research, Japan Agency for Marine-Earth Sci. & Tech., B200, Monobe, Nankoku, Kochi, 783-8502, Japan
AU: Yang, T F
EM: tyyang@ntu.edu.tw
AF: National Taiwan University, no. 1, Sec. 4, Roosevelt Rd., Taipei, 106, Taiwan
AU: Wang, Y
EM: wangys@moeacgs.gov.tw
AF: Taiwan Central Geological Survey, no. 2, Lane 109, Huasin St., Taipei, 235, Taiwan
AU: Lim, Y
EM: d93241002@ntu.edu.tw
AF: National Taiwan University, no. 1, Sec. 4, Roosevelt Rd., Taipei, 106, Taiwan
AB: Multiple flares, unusual chemosynthetic community, and authigenic carbonate were found on top of the Formosa Ridge in the passive margin of the Northeastern South China Sea. Very densely populated mussel ( Bathymodiolus platifrons) together with a type of white colored crab ( Shinkai cronieri) usually found in the hydrothermal vent indicated that methane and hydrogen sulfide maybe dominating this environment. The purpose of this research is to study the geochemical property of the environment and mechanism driving this unusual chemosynthetic community. A set of piston cores and ROV short core were collected and analyzed for pore water dissolved sulfide, chloride, sulfate and sediment carbonate content, organic carbon, AVS, pyrite concentrations, stable carbon and oxygen isotopes variations in carbonate. Near sea floor gas hydrate formation control pore water compositions adjacent to the plume. Both pore water chloride and sulfate showed unusually higher values near the gas plume, and radially outward until reaching normal seawater compositions away from the plume. At some locations, chloride concentrations also increase with increasing depth in cores, probably a result of gas hydrate dissolution after sampling. In addition, very high concentrations of pore water dissolved sulfide were also observed. Up to ~20 mM of dissolved sulfide were found in cores near the plume area. Methane provides extra carbon source for the observed rapid sulfate reduction and pyrite formation. Depending on the proximity to the seep, degree of sulfate depletion and pyrite formation in cores varies significantly. Sulfate depleted rapidly near seep; however, there was almost no depletion away from the seep. Very high concentrations of pyrite were also found near sediment/water interface adjacent to seep. The depth of maximum pyrite occur also varies, depending on the distance away from the seep. Authigenic carbonates (up to 70 wt percent) with very light stable carbon isotope, as low as -55 per mil, were found at depth. In addition, partially cemented mud and vent tube-like mudstone with lighter carbon isotopic signature were also found in some overlying sediment. Partially cemented vent-tubes are acting as gas conduit for gas migration. The abundance of B. platifrons and S. Cronieri, pore water chloride and sulfate, authigenic carbonate and its isotopic signatures indicated that seep methane and hydrogen sulfide are the primary driving mechanism for the observed chemistry variations and biological community.
DE: 4802 Anoxic environments (0404, 1803, 4834, 4902)
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4811 Chemosynthesis
DE: 4870 Stable isotopes (0454, 1041)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting