日本地球惑星科学連合2015年大会

講演情報

ポスター発表

セッション記号 M (領域外・複数領域) » M-IS ジョイント

[M-IS24] ガスハイドレートと地球環境・資源科学

2015年5月27日(水) 18:15 〜 19:30 コンベンションホール (2F)

コンビーナ:*戸丸 仁(千葉大学理学部地球科学科)、八久保 晶弘(北見工業大学環境・エネルギー研究推進センター)、森田 澄人(独立行政法人 産業技術総合研究所 地圏資源環境研究部門)

18:15 〜 19:30

[MIS24-P10] サハリン島沖ガスハイドレート胚胎域の間隙水溶存ガス

*八久保 晶弘1竹谷 敏2Olga VERESHCHAGINA3坂上 寛敏1南 尚嗣1山下 聡1高橋 信夫1庄子 仁1Young K. JIN4Anatoly OBZHIROV3 (1.北見工業大学、2.産業技術総合研究所、3.ロシア科学アカデミー太平洋海洋学研究所、4.韓国極地研究所)

キーワード:ガスハイドレート, 間隙水, 安定同位体, オホーツク海, サハリン島

We summarize characteristics of dissolved gas in pore water in sub-bottom sediments off Sakhalin Island, where gas hydrates were retrieved. Gas hydrates have been discovered at the northeastern, southeastern and southwestern Sakhalin Island in the cruises of LV31 (2003), LV32 (2003), LV36 (2005), and LV39 (2006) in the framework of hydro-Carbon Hydrate Accumulations in Okhotsk Sea (CHAOS) project, and those of LV47 (2009), LV50 (2010), LV56 (2011), LV59 (2012), LV62 (2013), and LV67 (2014) in the framework of Sakhalin Slope Gas Hydrate (SSGH) project. We retrieved sediment cores (184 cores in total) including gas hydrates (29 cores) in these cruises (R/V Akademik M. A. Lavrentyev).
The dissolved gases in the pore water were extracted according to a headspace gas method. Basically, 10 mL of sediment and 10 mL of saturated aqueous solution of NaCl with a small amount of benzalkonium chloride (preservative) were introduced into a 25 mL vial to create a 5 mL headspace. The headspaces were flushed with nitrogen or helium as an inert gas. The vials were then shaken thoroughly and stored overturned. Molecular and stable isotope compositions of these samples were measured in our laboratory (Kitami Institute of Technology).
The depths of sulfate-methane interface (SMI) distributed mainly 1-3 mbsf, and those of hydrate-bound core were shallower (30 cm to 1 m). The dissolved gases in pore water below the SMI depth were primarily methane (more than approximately 99% of the total hydrate-bound gas), although ethane, propane, CO2, and hydrogen sulfide were also detected. The molecular and isotopic compositions of dissolved gas in the pore water indicated that the sediment cores including gas hydrates contain 13C-rich methane and relatively high concentrations of 13C-rich ethane compared to other gas-rich sediment cores. The gas-rich sediment cores without gas hydrates are characterized by high C1/(C2+C3) ratios and 13C-depleted methane and ethane. We suggested the idea that small amount of thermogenic gas controlled ocuurrence of gas hydrate in the subsurface sediment off Sakhalin Island.