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Molecular and isotopic characteristics of gas hydrate-bound hydrocarbons in southern and central Lake Baikal |
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| Authors: | Akihiro Hachikubo Oleg Khlystov Alexey Krylov Hirotoshi Sakagami Hirotsugu Minami Yutaka Nunokawa Satoshi Yamashita Nobuo Takahashi Hitoshi Shoji Shin’ya Nishio Masato Kida Takao Ebinuma Gennadiy Kalmychkov Jeffrey Poort |
| Institution: | 1. Kitami Institute of Technology, 165 Koen-cho, Kitami, 090-8507, Japan 2. Limnological Institute, SB RAS, 3 Ulan-Batorskaya St., Irkutsk, 664033, Russia 3. I.S. Gramberg All-Russia Research Institute for Geology and Mineral Resources of the World Ocean (VNIIOkeangeologia), 1 Angliysky Ave., St. Petersburg, 190121, Russia 4. Shimizu Corporation, 3-4-17 Etchujima, Koto-ku, Tokyo, 135-8530, Japan 5. National Institute of Advanced Industrial Science and Technology, 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo, 062-8517, Japan 6. Vinogradov Institute of Geochemistry, SB RAS, 1-a Favorsky St., Irkutsk, 664033, Russia 7. Renard Centre of Marine Geology, Ghent University, Krijgslaan 281 s8, Ghent, 9000, Belgium 8. Laboratoire de Géosciences Marines, Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75005, France |
| Abstract: | We investigated the molecular composition (methane, ethane, and propane) and stable isotope composition (methane and ethane) of hydrate-bound gas in sediments of Lake Baikal. Hydrate-bearing sediment cores were retrieved from eight gas seep sites, located in the southern and central Baikal basins. Empirical classification of the methane stable isotopes (δ13C and δD) for all the seep sites indicated the dominant microbial origin of methane via methyl-type fermentation; however, a mixture of thermogenic and microbial gases resulted in relatively high methane δ13C signatures at two sites where ethane δ13C indicated a typical thermogenic origin. At one of the sites in the southern Baikal basin, we found gas hydrates of enclathrated microbial ethane in which 13C and deuterium were both highly depleted (mean δ13C and δD of –61.6‰ V-PDB and –285.4‰ V-SMOW, respectively). To the best of our knowledge, this is the first report of C2 δ13C–δD classification for hydrate-bound gas in either freshwater or marine environments. |
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