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Methane bubble fluxes in gas flares from bottom sediments in Lake Baikal were estimated for the first time using hydroacoustic methods. Earlier work has demonstrated the occurrence of gas seeps both inside and outside of areas where bottom simulating reflectors were identified in seismic profiles. Fluxes ranged from 14 to 216 tons per year, with the flux for the entire area of the central and southern basins ranging from 1,400 to 2,800 tons per year. Comparison with other water bodies showed that fluxes from the most intensive Baikal flares were similar to those in the Norwegian and Okhotsk seas. Gas hydrates decompose at the lower boundary of the gas hydrate stability zone due to sedimentation. Calculation of the amount of methane produced due to sedimentation gave a total of between 2,600 and 14,000 tons per year for the central and southern basins of the lake. Based on rough estimation, the total flux from shallow- and deep-water gas seeps is similar to the amount of methane produced due to sedimentation. This suggests that gas hydrates possibly occupy much more than 10 % of the pore volume near the base of the gas hydrate stability zone, or that there are other reasons for gas hydrate dissociation and bubble flux from these bottom sediments. [ABSTRACT FROM AUTHOR]

In September 2008, freshening of near-bottom water and an increase in concentration of suspended particles were observed in the western part of southern Lake Baikal. The reduction in the content of total dissolved solids was about 0.4-0.7 mg/kg (0.7 %), and average suspended particle concentration increased strongly to 6-9 mg/l, the background value being 0.2 mg/l. The spatial distribution of these waters was virtually identical to the focal area of the M6.2 Kultuk earthquake that occurred on 27 August 2008. It is suggested that there was a causal relationship between these two phenomena. Freshening of a significant amount (about 20 km) of near-bottom waters was plausibly caused by an input of poorly mineralized pore waters from bottom sediments as a result of dissociation of methane gas hydrates suspected to occur in the area. The energy radiated by the earthquake source was four orders of magnitude smaller than that needed to explain the observed freshening of near-bottom waters. This points to other mechanisms leading to seismic-induced sediment failure and possible subsequent hydrate dissociation in the case of the Kultuk earthquake. [ABSTRACT FROM AUTHOR]