Model of formation of double structure gas hydrates in Lake Baikal based on isotopic data

We measured the isotopic compositions of methane (C-1) and ethane (C-2) of hydrate-bound gas and of dissolved gas in pore water retrieved from bottom sediments in Lake Baikal. Both structure I (sI: 3% C-2) and II (sII: 14% C-2) gas hydrates are observed in the same sediment cores in Kukuy K-2 mud volcano. We found that C-2 delta D of sI gas hydrate is larger than that of sII, whereas C-1 delta C-13, C-1 delta D and C-2 delta C-13 values are practically the same in both hydrate structures. delta C-13 of C-1 and C-2 of hydrate-bound gas are several permil smaller than those in pore water, showing that the current pore water is not the source of gas hydrates. These findings lead to a new model where the sII gas hydrates were formed prior to the sI hydrates. Citation: Hachikubo, A., et al. (2009), Model of formation of double structure gas hydrates in Lake Baikal based on isotopic data, Geophys. Res. Lett., 36, L18504, doi:10.1029/2009GL039805.