Ninth international conference on - Marum

Abstracts of posters 77
surfaces and further formation of dome-shaped density structure. As a result, ring cyclonic water current has to
be generated under the ice. In the zone of the highest current velocities, a vertical water exchange increases and
the ice thickness rapidly decreases (or the ice is partly destructed). This process may be reflected as a ring
structure on the ice surface. Careful examination of available satellite images allowed us to establish similar
structures formed on the ice at the same region on April 1999, 2005, and 2008. Analogous ring structures were
also observed on the ice opposite the Turka River mouth (April 2008) (Fig. 2, right) and in the northern part of
Maloe More strait (May 2004, 2005).
Both the deep-water methane escapes from the bottom and the ring structures regularly appearing on the ice
surface may testify to the present activity of mud volcanoes in Lake Baikal. To evaluate contribution of different
factors (seismic activity, fluctuations of the lake level, etc.) into such activity, continuous observations need to
be organized in the future.
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Fig. 2. The ring structures on the Baikal ice recorded near the Krestovskii cape in April 2003 (left) and April
2008 (right).
Regional characteristics of isotopic composition of gas hydrates in Lake Baikal
A. Hachikubo 1 , O. Khlystov 2 , T. Zemskaya 2 , A. Krylov 1,3 , H. Sakagami 1 , H. Minami 1 , Y. Nunokawa 1 , H. Shoji 1 ,
S.Nishio 4 , M. Kida 5 , T. Ebinuma 5 , G. Kalmychkov 6 , J.Poort 7
1 Kitami Institute of Technology, 165 Koen-cho, Kitami 090-8507, Japan
2 Limnological Institute, SB RAS, 3 Ulan-Batorskaya St., Irkutsk 664033, Russia
3 Present address:All-Russia Research Institute for Geology and Mineral Resources
4 Shimizu Corporation, 3-4-17 Etchujima, Koto-ku, Tokyo 135-8530, Japan
5 Advanced Industrial Science and Technology, 2-17-2-1, Tsukisamu-Higashi, Sapporo 062-8517, Japan
6 Vinogradov Institute of Geochemistry, SB RAS, 1-a Favorsky St., Irkutsk 664033, Russia
7 Renard Centre of Marine Geology, Ghent University, Krijgslaan 281-S8, Ghent B-9000, Belgium
Gas hydrates are crystalline clathrate compounds composed of water and gas molecules that are stable at low
temperature, high partial pressure of each gas component, and high gas concentration. Ten years ago natural gas
hydrates were retrieved for the first time from the sublacustrine sediments of Lake Baikal and since then the
specifics of their formation process has been discussed by researchers. In an <strong>international</strong> collaborative
investigation program of Lake Baikal with the Limnological Institute SB RAS, Russia, since 2002, we collected
new gas hydrate samples from the lake bottom sediment in the following mud volcanoes and methane seep sites:
Malenky, Bolshoy, Malyutka, Peschanka, Goloustnoye Flare and Kukuy K-0 & K-2. Our study focussed on the
isotopic composition of guest gas in gas hydrates in order to understand their formation process and gas origin.
Whiticar et al. (1986) proposed a genetic classification diagram for natural gas using δ 13 C and δD of methane. In
the diagram, large and small δ 13 C values of methane indicate thermogenic and mic robial origins, respectively,
and δD of methane provides information on methyl-type fermentation or CO2 reduction in the microbial region.
Kida et al. (2006) concluded from isotopic signatures of Kukuy gas hydrates that the guest gas is of microbial
origin due to methyl-type fermentation and contains thermogenic methane and ethane. For the isotopic analyses
of carbon and hydrogen, a continuous flow-isotope ratio mass spectrometer (CF-IRMS, DELTA plus XP;
Thermo Finnigan) was used. Methane δ 13 C and δD of all observation sites were in the range of -70 to -55 ‰ and
-330 to -300 ‰, respectively, and indicated a microbial origin produced by methyl-type fermentation. Methane