MIS027-P01

会場:コンベンションホール

時間:5 月 22 日 10:30-13:00

オホーツク海サハリン島沖 Lavrentyev 海底断層南側の新領域で得られたガスハイドレートの特徴
Characteristics of hydrate-bound hydrocarbons retrieved from southern Lavrentyev seabedfault, the Sea of Okhotsk
八久保 晶弘 1∗ , 坂上 寛敏 1 , 南 尚嗣 1 , 山下 聡 1 , 高橋 信夫 1 , 庄子 仁 1 , ジン ヤン 2 , ヴェレシャーギナ オルガ 3 , オブジロ
フ アナトリー 3
Akihiro Hachikubo1∗ , Hirotoshi Sakagami1 , Hirotsugu Minami1 , Satoshi Yamashita1 , Nobuo Takahashi1 , Hitoshi Shoji1 , Young,K. Jin2 , Olga Vereshchagina3 , Anatoly Obzhirov311

北見工業大学, 2 韓国極地研究所, 3 V.I. イリチェフ太平洋海洋学研究所
Kitami Institute of Technology, 2 Korea Polar Research Institute, 3 Pacific Oceanological Institute, FEB RAS

We report molecular and isotopic compositions of hydrate-bound hydrocarbons in the new seepage sites of offshore Sakhalin
Island, the Sea of Okhotsk. More than ten gas seep sites have been discovered since 1990s in the north area of Lavrentyev Fault
and hydrate-bearing sediments were recovered (Ginsburg et al. , 1993; Hachikubo et al. , 2010). These sites often accompany
with gas plumes from the sea floor and gas hydrates exist in a shallow sediment layer. Recently, Sakhalin Slope Gas Hydrate(SSGH) project was started from 2007 and we retrieved sediment cores from the southern area of Lavrentyev Fault during theSSGH09 and SSGH10 cruises in 2009-2010. We obtained the samples of hydrate-bound gas and dissolved gas in pore water onboard, and we measured molecular and stable isotope compositions of them. Empirical classification of the methane stable isotopes; delta 13 C and delta D according to Whiticar et al. (1986) and Schoell (1988) indicated their microbial origin via carbonate
reduction. Profiles of methane concentration in the pore water suggested a shallow SMI (sulfate-methane interface). SMI depth
was estimated as 30-50cm from the sea floor in the case of hydrate-bearing cores, and around 2m from the sea floor in the caseof gas-rich cores. Molecular compositions of hydrate-bound gas were almost the same in both northern and southern areas ofLavrentyev Fault. Stable isotope compositions of hydrate-bound gas were concentrated in the range of -204.6 permil to -196.7
permil for delta D and -66.0 permil to -63.2 permil for delta 13 C in the north area (Hachikubo et al. , 2010). On the other hand,both isotopes were more depleted in the south area about 6 permil in 13 C and 7 permil in deuterium, respectively, suggested much
more active microbial processes in the shallow sediment. Isotopic difference in delta D between hydrate-bound and dissolved
gases was about 5 permil at several sites, indicating that the gas hydrates formed from the current gas in pore water (Hachikuboet al. , 2009).
Ginsburg, G.D., V.A. Soloviev, R.E. Cranston, T.D. Lorenson, K.A. Kvenvolden (1993) Gas hydrates from the continental
slope, offshore Sakhalin Island, Okhotsk Sea. Geo-Mar. Lett. , 13(1), 41-48, doi:10.1007/BF01204391.
Hachikubo A, O. Khlystov, A. Manakov, M. Kida, A. Krylov, H. Sakagami, H. Minami, N. Takahashi, H. Shoji, G. Kalmychkov, J. Poort (2009) Model of formation of double structure gas hydrates in Lake Baikal based on isotopic data. Geophys. Res. Lett. ,36, L18504, doi:10.1029/2009GL039805.
Hachikubo, A., A. Krylov, H. Sakagami, H. Minami, Y. Nunokawa, H. Shoji, T. Matveeva, Y. K. Jin, A. Obzhirov (2010)
Isotopic composition of gas hydrates in subsurface sediments from offshore Sakhalin Island, Sea of Okhotsk. Geo-Mar. Lett. ,30, 313-319, doi:10.1007/s00367-009-0178-y.
Schoell, M. (1988) Multiple origins of methane in the earth. Chem. Geol. , 71, 1-10.
Whiticar, M.J., E. Faber, M. Schoell (1986) Biogenic methane formation in marine and freshwater environments: CO2 reduction vs. acetate fermentation - Isotope evidence. Geochim. Cosmochim. Acta , 50, 693-709.
キーワード: ガスハイドレート, 安定同位体, オホーツク海
Keywords: gas hydrate, stable isotope, Sea of Okhotsk