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Bubble the gas outlet from the bottom sediments map

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Gas bubble emissions from bottom sediments of Lake Baikal

Methane emissions from bottom sediments in Lake Baikal have been known for a long time. Even the first travelers, who visited the lake in the 17th century, noticed gas emissions. Later gas emissions in Baikal were explored by the East Siberian Branch of the Russian Imperial Geographical Society. A review of the available materials on gas seeps in Baikal is presented in the publication [Granin and Granina, 2002]. A new stage of research on gas seeps in Baikal started after the discovery of gas hydrates [Kuzmin et al., 1998] and mud volcanoes at the bottom of the lake [Van Rensbergen et al., 2002] at the turn of the 20th century.

Gas seeps are found in oceans, seas and freshwater bodies. To study gas seeps hydroacoustic methods are used, as they enable an extensive search due to the strong backscattering of sound from the bubbles of floating-up gas. To locate and monitor the activity of gas plumes a digital record of acoustic signals of the echo sounders FURUNO, installed on the research vessels “G. Yu. Vereshchagin”, “Titov” and “Papanin”, was organized.

We subdivide gas seeps into shallow- and deepwater [Granin et al., 2010]. Deepwater gas seeps (red triangles on the map) are the ones that are located at depths greater than the depth of the gas hydrate stability (380 m); gas seeps, located at shallower depths (blue circles), belong to shallow-water gas seeps.

A substantial proportion of the shallow gas seeps are located near the Selenga river delta and on the Posolskaya bank. Multi-year monitoring of the activity of gas seeps made it possible to identify long-term and periodic gas shows. A maximum flare height of more than 1000 m was recorded in the area of ​​the mud volcano Malenky on June 23, 2011 from the RV “Titov”. According to the echo sounders data, the rise rates of gas bubbles reach 25 cm/s or more. In the area of plumes there is a near-bottom layer, where the temperature gradient is equal to the adiabatic one. This is indicative of a complete mixing of a significant layer of water as a result of the gas emissions [Granin et al.]

Using the acoustic sounding, a gas flow from bottom sediments was estimated. The estimation of the flow was made for several deepwater plumes. For different plumes the methane flow from the bottom sediments of Lake Baikal ranged from 14 to 216 tons per year. Comparing the result obtained with corresponding estimates for other water bodies, it may be said that the gas flow for the largest bottom gas seeps in Lake Baikal is corresponding to the flows in the Norwegian Sea and the Sea of ​​Okhotsk [Granin et al., 2-12].

References

Granin, N. G., Granina, L. Z. (2002). Gas hydrates and gas venting in Lake Baikal. Russ. Geol. Geophys, 43(7), p 629-637.

Kuzmin, M. I., Kalmychkov, G. V., & Gelety, V. F. (1998). The first finding of gas hydrates in the sedimentation mass of Lake Baikal. Proceedings of the Russian Academy of Sciences, 362(4). p 541-543.

Van Rensbergen, P., De Batist M., Klerkx J., Hus R., Poort J., Vanneste M., Granin N., Khlystov O., & Krinitsky P. (2002). Sublacustrine mud volcanoes and methane seeps caused by dissociation of gas hydrates in Lake Baikal. Geology, 30(7). p 631-634.

Granin, N. G., Makarov, M. M., Kucher, K. M., & Gnatovsky, R. Y. (2010). Gas seeps in Lake Baikal: Detection, distribution, and implications for water column mixing. Geo-Marine Letters, 30(3-4). p 399-409.

Granin N. G., Muyakshin, S. I., Makarov, M. M., Kucher, K. M., Aslamov, I. A., Granina, L. Z., & Mizandrontsev, I. B. (2012). Estimation of methane flows from bottom sediments of Lake Baikal. Geo-Marine Letters, 32(5-6). p 427-436. DOI 10.1007/s00367-012-0299-6

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