Abstract
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.
Highlights
Methane production in inland freshwater bodies is an intensive area of ongoing research due to the greenhouse potential of methane[1]
This paper describes the first evidence of methane hydrates emerging to the surface of Lake Baikal and validated by photo and video records
This study provides novel evidence that methane hydrates released from sediment at 500–1000 m depths can reach the surface of Lake Baikal
Summary
Methane production in inland freshwater bodies is an intensive area of ongoing research due to the greenhouse potential of methane[1]. Several recent studies have suggested that methane production and transport in lakes can be highly variable and may include significant methane production within the oxygen-rich upper water column[5,9]. These results demonstrate that methane release from well-oxygenated lakes may not always be negligible[10]. Zhang and Xu’ll[27] performed numerical modeling of a methane-seawater system along a T-P-depth profile similar to that of Blake Ridge (east of the U.S South Carolina coast) These researchers found that only methane hydrate fragments larger than 9 cm in radius could rise through a 530 m water column and reach the ocean surface. Analysis of biogenic-terrigenous sedimentary particles within the ice (the concentration of which was less than 0.8 g L−1) suggested that they were derived from the littoral zone of the lake, but methane analyses were not conducted[31]
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