Stable isotopic evidence for microbial ethane in Lake Baikal gas hydrates

  • Hachikubo A. 1
  • Kimura H. 1
  • Kamata R. 1
  • Sakagami H. 1
  • Minami H. 1
  • Yamashita S. 1
  • Khlystov O. 2
  • Kalmychkov G. 3
  • De Batist M. 4
  • 1 Kitami Institute of Technology, 165 Koen-cho, Kitami 090-8507, Japan
    2 Limnological Institute, Siberian Branch of the Russian Academy of Sciences, Ulan-Batorskaya Str., 3, Irkutsk 664033, Russia
    3 Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky Str., 1-a, Irkutsk 664033, Russia
    4 Renard Centre of Marine Geology, Ghent University, Krijgslaan 281s8, 9000, Ghent, Belgium
Keywords: gas hydrate, ethane, microbial gas, isotopic fractionation, gas origin

Abstract

In the framework of Multi-phase Gas Hydrate Project, near-surface gas hydrates were retrieved from the southern and central Baikal basins. In this report, we summarize characteristics of hydrate-bound hydrocarbons retrieved at Lake Baikal and focus on hydrate-bound ethane and its gas origin. The information of molecular composition of volatile hydrocarbons and their stable isotopes showed that the origin of hydrate-bound gas distributes in the fields of microbial, thermogenic, and their mixed-gas. As for stable isotope of ethane, 13C and D distribute from 69 to 23 V-PDB, and from 313 to 185 V-SMOW, respectively. Light ethane in 13C also depleted in D, indicating that the isotopically light ethane depleted in 13C and D is generated by a microbial process, and the origin of hydrogen in ethane molecules is thought to be lake water, same as methane.

Published
2020-09-07
Section
Articles