Stable isotopic evidence for microbial ethane in Lake Baikal gas hydrates

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.