HR: 1340h
AN: OS23A-1041    [Abstracts]
TI: Discovery of "Hydrothermal" Chemosynthetic Community in a Cold Seep Environment, Formosa Ridge: Seafloor Observation Results from First ROV Cruise, off Southwestern Taiwan
AU: * Machiyama, H
EM: bucci@jamstec.go.jp
AF: Kochi Inst. Core Sample Res., JAMSTEC, 200 Monobe-otsu, Nankoku, 783-8502, Japan
AU: Lin, S
EM: swlin@ntu.edu.tw
AF: Inst. Oceanography, National Taiwan Univ., No.1, Sec. 4, Roosevelt Road, Taipei, 106, Taiwan
AU: Fujikura, K
EM: fujikurak@jamstec.go.jp
AF: Extremobiosphere Res. Center, JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061, Japan
AU: Huang, C
EM: huangcy@mail.ncku.edu.tw
AF: Dept. Earth Sciences, National Cheng Kung Univ., 1, University Road, Tainan, 701, Taiwan
AU: Ku, C
EM: 93642003@cc.ncu.edu.tw
AF: Inst. Geophysics, National Central Univ., Jhongda Rd. 300, Jhong Li, 320, Taiwan
AU: Lin, L
EM: lhlin@ntu.edu.tw
AF: Dept. Geosciences, National Taiwan Univ., No.1, Sec. 4, Roosevelt Road, Taipei, 106, Taiwan
AU: Liu, C
EM: csliu@ntu.edu.tw
AF: Inst. Oceanography, National Taiwan Univ., No.1, Sec. 4, Roosevelt Road, Taipei, 106, Taiwan
AU: Morita, S
EM: morita-s@aist.go.jp
AF: Geological Survey of Japan, AIST, 1-1-1, Higashi, Tsukuba, 305-8567, Japan
AU: Nunoura, T
EM: takuron@jamstec.go.jp
AF: Extremobiosphere Res. Center, JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061, Japan
AU: Soh, W
EM: soh@jamstec.go.jp
AF: Kochi Inst. Core Sample Res., JAMSTEC, 200 Monobe-otsu, Nankoku, 783-8502, Japan
AU: Toki, T
EM: toki@sci.u-ryukyu.ac.jp
AF: Dept. Chemistry, Biology, and Marine Science, Univ. Ryukyus, 1, Senbaru, Nishihara-cho, 903-0213, Japan
AU: Yang, T F
EM: tyyang@ntu.edu.tw
AF: Dept. Geosciences, National Taiwan Univ., No.1, Sec. 4, Roosevelt Road, Taipei, 106, Taiwan
AB: First ROV diving survey has been conducted around the selected three sites (Formosa Ridge, Sites C and G) in offshore SW Taiwan, where gas hydrate broadly occurs within the thick Quaternary marine sediments. The Formosa Ridge and Site G are located in the South China Sea Continental Slope, whereas Site C is located in the frontal portion of a fault-bend fold in the accretionary wedge off SW Taiwan. Large, dense chemosynthetic communities were discovered at water depth of about 1120 - 1140 m on the top of the Formosa Ridge by direct observation using ROV Hyper-Dolphin of JAMSTEC. Colonies are distributed in depressions or fissures of large, carbon-depleted authigenic carbonates. The community is dominated by deep- sea mussel, Bathymodiolus platifrons, and galatheid crab, Shinkaia crosnieri. Most of species corresponds to those of hydrothermal vent fields in the Okinawa Trough, such as the Hatoma Knoll and the Iheya Ridge. Methane gas bubbles were found within the colony, and methane hydrate was also found beneath the aggregation of B. platifrons, which is harboured endosymbiont methanotroph in their gill in the Okinawa Trough. On the other hand, S. crosnieri from the Okinawa Trough culture numerous epibiont sulfur-oxidizing bacteria on their carapace. Therefore, they require high concentration of H₂S from the subseafloor fluids. Single channel seismic profiles show the presence of clear BSR underneath the Formosa Ridge, and suggest the possible upward migration of gassy fluids beneath the top of the ridge. Therefore, the ghydrothermalh chemosynthetic communities are supported by unusual high concentrations of methane and H₂S fluids from the subseafloor. This is first discovery of "hydrothermal" chemosynthetic communities in cold seep environments of the world. No active seeps and the related phenomena are found around the Site G. Large seep carbonates around the summit are often covered by mud veneer and organisms. Therefore, this mud volcano is inferred to be terminated its activity. Swath bathymetry around Site C probably shows the presence of a mud volcano on the seafloor. Unfortunately, bad sea state didnft permit to finish our mission for ROV survey.
DE: 0400 BIOGEOSCIENCES
DE: 3004 Gas and hydrate systems
DE: 3045 Seafloor morphology, geology, and geophysics
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting