Methane with Abnormally High δ13C and δD Values from the Coastal Hot Springs in Lake Baikal

We studied the composition and isotopic characteristics (δ13C and δD) of hydrocarbon gases from the Kotelnikovsky, Zmeiny, and Goryachnisky hot springs located in the coastal zone of Lake Baikal. Of greatest interest is the Zmeiny Spring located on the eastern coast, where the methane has abnormally high values of δ13C (up to +11‰) and δD (up to +267‰). These values are related to the fractionation of carbon and hydrogen isotopes during the oxidation of microbial methane. The δ13C-C1 value (‒40.2‰) in the Goryachinsky Spring can formally indicate the thermogenic origin of methane. However, the modification of carbon isotope composition in this spring due to methane oxidation is more likely, because gas from the Goryachinsky Spring contains the microbial methane as admixture. Isotopic characteristics typical of microbial gases undistorted by secondary oxidation (δ13C-C1 = ‒61.5‰, δD-C1 = ‒230.2‰, δ13C-C2 = ‒56.6‰) are recorded in the Kotelnikovsky Spring northwest of Lake Baikal.