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This study focuses on heat and mass exchange processes in hydrate foam. The foam was formed by methane bubble collection in Lake Baikal at a depth of 1400 m with a trap in the form of inverted beaker. The bubbles entering in the trap were transformed into solid hydrate foam due to low temperature and high pressure, i.e. thermobaric conditions preferable for hydrate formation. The boundary between forming hydrate foam and the water propagated slowly from top to bottom along the trap. As soon as the hydrate boundary crossed the location of temperature sensor, the temperature jump by ~ + 1.1 °C was recorded. After that during 3 h the temperature relaxes to an asymptotic magnitude which exceeded the temperature of ambient water by 0.3 °C. During the following ascent of the trap to the lake surface we recorded high amplitude oscillations of the temperature inside the foam. However the temperature was sharply stabilized on the constant level -0.25 °C once the trap left the hydrate stability zone located at a depth below 380 m. It was found that the temperature in the foam during the ascent is controlled by the performing of the work by foam gas against the forces of hydrostatic pressure and the absorption of heat by the decomposition of hydrate. [ABSTRACT FROM AUTHOR]

Jelly-like microbial mat samples were collected from benthic surfaces at the St. Petersburg methane seep located in Central Baikal. The concentrations of certain ions, specifically chloride, bromide, sulphate, acetate, iron, calcium, and magnesium, were 2–40 times higher in the microbial mats than those in the pore and bottom water. A large number of diatom valves, cyanobacteria, and filamentous, rod-shaped and coccal microorganisms were found in the samples of bacterial mats using light, epifluorescence and scanning microscopy.Comparative analysis of a 16S rRNA gene fragment demonstrated the presence of bacteria and archaea belonging to the following classes and phyla: Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Verrucomicrobia, Cytophaga-Flavobacteria-Bacteroidetes, Cyanobacteria, and Euryarchaeota. The chemical composition and phylogenetic structure of the microbial community showed that the life activity of the mat occurs due to methane and its derivatives involved. Values of δ13C for the microbial mats varied from −73.6‰ to −65.8‰ and for animals from −68.9‰ to −36.6‰. Functional genes of the sequential methane oxidation (pmoAandmxaF) and different species of methanotrophic bacteria inhabiting cold ecosystems were recorded in the total DNA. Like in other psychroactive communities, the destruction of organic substances forming formed as a result of methanotrophy, terminates at the stage of acetate formation in the microbial mats of Lake Baikal (1,400 m depth). Its further transformation is limited by hydrogen content and carried out in the subsurface layers of sediments. [ABSTRACT FROM PUBLISHER]