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Isotopic composition of gas hydrates in subsurface sediments from offshore Sakhalin Island, Sea of Okhotsk

Cited 10 time in scopus
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Title
Isotopic composition of gas hydrates in subsurface sediments from offshore Sakhalin Island, Sea of Okhotsk
Other Titles
오호츠크해 사할린섬 주변에서 획득된 퇴적물 내 가스하이드레이트의 동위원소 조성
Authors
Anatoly Obzhirov
Tatiana Matveeva
Alexey Krylov
Hitoshi Shoji
Jin, Young Keun
Yutaka Nunokawa
Hirotsugu Minami
Hirotoshi Sakagami
Akihiro Hachikubo
Subject
Geology; Oceanography
Keywords
C1/C2; Sea of Okhotsk; gas hydrate; δD; δ¹³C
Issue Date
2010
Publisher
Springer
Citation
Anatoly Obzhirov, et al. 2010. "Isotopic composition of gas hydrates in subsurface sediments from offshore Sakhalin Island, Sea of Okhotsk". GEO-MARINE LETTERS, 30(3-4): 313-319.
Abstract
Hydrate-bearing sediment cores were retrieved from recently discovered seepage sites located offshore Sakhalin Island in the Sea of Okhotsk. We obtained samples of natural gas hydrates and dissolved gas in pore water using a headspace gas method for determining their molecular and isotopic compositions. Molecular composition ratios C1/C2+ from all the seepage sites were in the range of 1,500?-50,000, while δ¹³C and δD values of methane ranged from ??66.0 to??63.2‰VPDB and ??204.6 to ??196.7‰VSMOW, respectively. These results indicate that the methane was produced by microbial reduction of CO2. δ¹³C values of ethane and propane (i.e., ??40.8 to ??27.4‰VPDB and ??41.3 to ??30.6‰VPDB, respectively) showed that small amounts of thermogenic gas were mixed with microbial methane. We also analyzed the isotopic difference between hydrate-bound and dissolved gases, and discovered that the magnitude by which the δD hydrate gas was smaller than that of dissolved gas was in the range 4.3??16.6‰?, while there were no differences in δ¹³C values. Based on isotopic fractionation of guest gas during the formation of gas hydrate, we conclude that the current gas in the pore water is the source of the gas hydrate at the VNIIOkeangeologia and Giselle Flare sites, but not the source of the gas hydrate at the Hieroglyph and KOPRI sites.
URI
http://repository.kopri.re.kr/handle/201206/6151
DOI
http://dx.doi.org/10.1007/s00367-009-0178-y
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