Methane hydrate emergence from Lake Baikal: direct observations, modelling, and hydrate footprints in seasonal ice cover.

This paper provides a novel report of methane hydrates rising from bottom sediments to the surface of Lake Baikal, validated by photo and video records. The ascent of hydrates in the water column was confirmed by hydroacoustic data showing rising objects with velocities significantly exceeding the typical speeds (18-25 cm s-1) of gas bubbles. Mathematical modelling along with velocity and depth estimates of the presumed methane hydrates coincided with values observed from echograms. Modelling results also showed that a methane hydrate fragment with initial radius of 2.5 cm or greater could reach the surface of Lake Baikal given summer water column temperature conditions. Results further show that while methane bubbles released from the deep sedimentary reservoir would dissolve in the Lake Baikal water column, transport in hydrate form is not only viable but may represent a previously overlooked source of surface methane with subsequent emissions to the atmosphere. Methane hydrates captured within the ice cover may also cause the formation of unique ice structures and morphologies observed around Lake Baikal. Sampling of these ice structures detected methane content that exceeded concentrations measured in surrounding ice and from the atmosphere demonstrating a link with the methane transport processes described here.

Spatial distribution of methane over Lake Baikal surface.

The results of application of a high sensitivity methane laser detector to investigations of the methane concentration in the atmosphere over Baikal lake are presented as well as methane flows from the water into the atmosphere. The measurements were conducted at a stationary station and aboard the research vessel "Vereschagin" during two summer expeditions in 2003 and 2004. Mean background concentration was equal to (2.00+/-0.16) ppm in August 2003 and (1.90+/-0.07) ppm in June 2004. The areas of methane emission through the water's surface are found to be distinctly localized and to have a characteristic size of about 150-300 m in diameter. The methane concentration in the centers of these areas can reach approximately 27 ppm. Methane flows into the atmosphere in some Baikal regions were measured as well.