HR: 09:00h
AN: OS41C-04 INVITED [Abstracts]
TI: Gas Hydrate Layer and Prominent Flares of Gas Plumes in Naoetsu Basin, Eastern Margin of Japan
Sea.
AU: * Matsumoto, R
EM: ryo@eps.s.u-tokyo.ac.jp
AF: University of Tokyo, Hongo Bunkyo-ku, Tokyo, 113-0033
Japan
AU: Tomaru, H
EM: hitoshi@earth.rochester.edu
AF: Rochester University, Uutchinson Hall, Rochester, 14627
United States
AU: Hiruta, A
EM: hiruta@eps.s.u-tokyo.ac.jp
AF: University of Tokyo, Hongo Bunkyo-ku, Tokyo, 113-0033
Japan
AU: Ishida, Y
EM: yasushi@eps.s.u-tokyo.ac.jp
AF: University of Tokyo, Hongo Bunkyo-ku, Tokyo, 113-0033
Japan
AU: Takeuchi, R
EM: lika@eps.s.u-tokyo.ac.jp
AF: University of Tokyo, Hongo Bunkyo-ku, Tokyo, 113-0033
Japan
AU: Snyder, G
EM: gsnyder@rice.edu
AF: Rice University, University, Houston, 14627
United States
AU: Kotani, R
EM: Kota@eps.s.u-tokyo.ac.jp
AF: University of Tokyo, Hongo Bunkyo-ku, Tokyo, 113-0033
Japan
AU: Kotani, R
EM: Kota@eps.s.u-tokyo.ac.jp
AF: Rice University, University, Houston, 14627
United States
AU: Okuda, Y
EM: okuda.gsj@aist.go.jp
AF: Geological Survey, Higashi, Tukuba, 305-0046
Japan
AU: Sato, M
EM: mikio-sato@aist.go.jp
AF: Geological Survey, Higashi, Tukuba, 305-0046
Japan
AU: Numanami, H
EM: hnuma@kasei-gakuin.ac.jp
AF: Tokyo Kasei Gakuin University, Aihara2600 Machida, Tokyo, 194-0292
Japan
AU: Aoyama, C
EM: aoyamac@hotmail.com
AF: Dokken, Nishi-Shinbashi, Tokyo, 105-0003
Japan
AU: Hiromatsu, M
EM: sti-555@mx12.freecom.ne.jp
AF: Chiba University, Nishichiba, Chiba, 263-0024
Japan
AU: Lu, H
EM: Hailong.Lu@nrc-cnrc.gc.ca
AF: NRC Canada, 100 Sussex Drive, Ottawa, K1A0R6
Canada
AU: Matsuda, N s
EM: nilo@petrobras.com.br
AF: Petrobras, Chile Ave, Rio de Janeiro, 20031912
Brazil
AU: Lu, Z
EM: hitoshi@earth.rochester.edu
AF: Rochester University, Uutchinson Hall, Rochester, 14627
United States
AU: Takeuchi, E
EM: s45105@mail.ecc.u-tokyo.ac.jp
AF: University of Tokyo, Hongo Bunkyo-ku, Tokyo, 113-0033
Japan
AU: Goto, T
EM: tgoto@jamstec.go.jp
AF: JAMSTEC, Natsushima, Yokosuka, 237-0061
Japan
AU: Machiyama, H
EM: bucci@jamstec.go.jp
AF: JAMSTEC, Natsushima, Yokosuka, 237-0061
Japan
AU: Toh, H
EM: toh@sci.toyama-u.ac.jp
AF: JAMSTEC, Natsushima, Yokosuka, 237-0061
Japan
AU: Komatsubara, J
EM: j.komatsubara@aist.go.jp
AF: Geological Survey, Higashi, Tukuba, 305-0046
Japan
AB:
Large pockmarks and mounds, 50 to 500 m in diameter, were observed to develop on the NNE-SSW trending Umitaka Spur,
approsimately 30 km off Naoetsu in the eastern margin of Japan Sea. Quantitative Echo Sounder of R/V Umitaka-maru and SEABAT
of R/V Natsushima clearly demonstrated a number of prominent flares of gas plumes, 500 to 600 m high, over the pockmark and
mound zones at water depth of 890 to 950 on the Spur. ROV-Dolphin of Natsushima identified rising _gbubbles_h in the
intermediate waters over the mound area. Methane concentration of seawaters over the area is generally high, 4 to 6 mmol/L,
with extremely high spikes up to 180 mmol/L. Shallow waters at around 200 to 300 m is remarkably high, 18 to 35 mmol/L. CTD
has revealed that the temperature of waters below 300 m are quite low, 0.25?_qC to 1.5?_qC, whereas it increases up to 25?_qC
in surface waters. Thus the temperature and pressure conditions of the deep and intermediate waters are favorable for the
formation of methane hydrates. Then, the bubbles on the seafloor are likely to form gas hydrates, float upward until they
reach the warm waters. 3D seismic survey (JOGMEC, 2003) has revealed strong, flat-lying BSRs at about 140 mbsf on the Spur,
and chaotic gas-charged units (_ggas columns_h) of about 1 to 3 km in diameter below the pockmark and mound zones. Also, very
strong but discontinuous BSRs occur at around 140 mbsf within _ggas columns_h. Piston coring successfully recovered either
massive or nodular gas hydrates from the top 2 to 4 meters interval at 6 piston sites on the mounds Deep-tow camera of R/V
Kaiyo and ROV-Dolphin demonstrated wide distribution of white _gbacterial_h mat zones, and sea-floor exposure of gas
hydrates. Gas hydrates are all characterized by thermogenic methane with carbon isotopic values of -40 permil PDB. Japan Sea
began to open in the last 25 Ma, had been expanding in EW direction. However, recently, probably 2 to 5 Ma, Japan Sea started
to shrink. This tectonic event has been called _gInversion Tectonics_h. The formation of the Umitaka Spur may have been
related with the inversion tectonics of Japan Sea. Likewise, magnificent methane plumes and the migration of the deep-seated
thermogenic gases in Naoetsu basin of the hydrocarbon province of Japan are thought to have been controlled by the regional
tectonics.
DE: 1861 Sedimentation (4863)
DE: 4802 Anoxic environments (0404, 1803, 4834, 4902)
DE: 4803 Analytical chemistry
DE: 9320 Asia
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005