MIS09-P14

日本地球惑星科学連合2016年大会

オホーツク海網走沖の天然ガスハイドレートの特徴
Characteristics of natural gas hydrate retrieved off Abashiri, the Sea of Okhotsk*八久保 晶弘1、竹谷 敏2、小西 正朗1、坂上 寛敏1、山崎 新太郎1、南 尚嗣1、山下 聡1、髙橋 信夫1、庄子
仁1*Akihiro Hachikubo1, Satoshi Takeya2, Masaaki Konishi1, Hirotoshi Sakagami1, Shintaro Yamasaki1,Hirotsugu Minami1, Satoshi Yamashita1, Nobuo Takahashi1, Hitoshi Shoji1
1.北見工業大学、2.産業技術総合研究所
1.Kitami Institute of Technology, 2.National Institute of Advanced Industrial Science andTechnology (AIST)In the area of southwestern margin of the Sea of Okhotsk, an existence of natural gas hydrate has
been expected using seismic data. Yamamoto et al. (2002) suggested existence of natural gas hydrate
off Shiretoko, the Sea of Okhotsk, by a long piston coring. Recovery of sediment core for gas
hydrate started in the cruise of TK11 in 2011 in the framework of joint research between Kitami
Institute of Technology and University of Tokyo, and obtained gas-rich sediment cores off Abshiri.
Gas hydrate crystals were first retrieved in the cruise of UT12 (T/S Umitaka-Maru) in 2012. New
hydrate-bearing sites were also discovered in the cruise of NT13-20 (R/V Natsushima in 2013. We
planned operations using T/S Oshoro-Maru, and obtained sediment cores and gas hydrates at this areain the cruise of OS249 (2012), OS263 (2013), and C020 (2015).
Gas hydrate crystals were obtained and stored in liquid nitrogen for Raman spectroscopic analysis
and calorimetry. Samples of hydrate-bound gas were obtained onboard and stored in 5-mL vials, andsediment gas were also obtained using a headspace gas method. We measured molecular and stableisotope compositions of these samples. We summarized the results as follows:
1) Gas hydrates belong to the cubic structure I, containing methane (more than 99%) and hydrogensulfide (less than 1%). C1/C2+ ranges from 5,500 to 5,800.
2) Hydration number is estimated as 6.03±0.04, agrees well with 6.04±0.03 for synthetic methane
hydrate (Sum et al., 1997).
3) Dissociation heat from hydrate to gas and water is estimated as 55.1±0.3 [kJ/mol], agrees wellwith 54.19±0.28 [kJ/mol] for synthetic methane hydrate (Handa, 1986).
4) Hydrate-bound gas is of microbial origin according to C1/C2+ and stable isotopes ofhydrocarbons, however, delta 13C of ethane seems relatively large.
5) Gas hydrate in the NT13-20 PC06 core contains trace amount of ethane (several ppm), whereas thatin the NT13-20 PC02 core contains about 100ppm of ethane.
6) SMI (sulfate-methane interface) depth of the sediment cores are less than 1m, indicating highmethane flux off Abashiri.
We appreciate the support of the crew onboard R/V Natsushima during the NT13-20 cruise, and T/SOshoro-Maru during the cruises of OS249, OS263, and C020. This study was supported by theGrant-in-Aid for Scientific Research (B) 25289142 and 26303021 of the Japan Society for thePromotion of Science (JSPS).
Handa (1986) Compositions, enthalpies of dissociation, and heat capacities in the range 85 to 270 K
for clathrate hydrate of methane, ethane, and propane, and enthalpy of dissociation of isobutane
hydrate, as determined by a heat-flow calorimeter. J Chem Thermodyn 18: 915-921.
Sum et al. (1997) Measurement of clathrate hydrates via Raman spectroscopy. J Phys Chem B 101:7371-7377.

©2016. Japan Geoscience Union. All Right Reserved.

- MIS09-P14 -MIS09-P14

日本地球惑星科学連合2016年大会

キーワード：ハイドレート、オホーツク海、安定同位体
Keywords: hydrate, the Sea of Okhotsk, stable isotope©2016. Japan Geoscience Union. All Right Reserved.

- MIS09-P14 -