Ninth international conference on - Marum

Abstracts of oral presentations 65
sediment surface, high sulfide fluxes, mineral precipitates (e.g., authigenic carbonate and gas hydrates), and
diagnostic stable-isotope signals in inorganic and organic phases.
Here we present fluxes and consumption rates from different cold seep systems including mud volcanoes,
pockmarks, gas and asphalt seeps from the Arctic region (Hakon Mosby Mud Volcano), the Eastern
Mediterranean (Amon Mud Volvano, Central Pockmarks), the Golf of Mexico (Chapopote), the Japan Trench
(Calyptogena accumulations). We compare in situ oxygen consumption rates as an indicator for the (micro-
)biological and chemical activities, as well as methane discharge and subsurface consumption. Our data show
that cold seeps are heterogeneous ecosystems in which abiotic as well as biotic processes are strongly influenced
by fluid and gas fluxes often varying in space and time. In situ measurements reveal that at geostructure scale,
specific habitats with distinct O2 consumption and methane emission rates can be identified. Combining habitatspecific
rate measurements with video observation enables us to estimate the spatial distribution of the different
habitats providing first data on methane and oxygen budgets of a variety of cold seeps world wide. By scaling
our measured rates from local to regional and global levels, we evaluate the ecological importance of cold seeps,
which is crucial to understand the role of methane in the global carbon cycle.
Microbial communities in sediments of Lake Baikal mud volcanoes
T.I. Zemskaya 1 , O.V. Shubenkova 1 , S.M. Chernitsina 1 , A.V. Egorov 2 , G.V. Kalmychkov 3 , T.P. Pogadaeva 1 ,
O.M. Khlystov 1 , S. Buryukhaev 4 , B.B. Namsaraev 4
1 Limnological Institute SB RAS, 3 Ulan-Batorskaya st., Irkutsk 664033, Russia
2 P.P. Shirhov’s Institute of Oceanology, 36 Nachimovskii pr., Moscow 117997, Russia
3 A.P. Vinogradov’s Institute of Geochemistry, 1а Favorskii st., Irkutsk 664033, Russia
4 Institute of General and Experimental Biology, 6 Sach’yanovoi st., Ulan-Ude 670047, Russia
Till now Lake Baikal is the only freshwater reservoir where methane hydrates have been discovered (Kuzmin et
al., 1997; Klerkx et al., 2003). Subsurface deposits of gas hydrates are located in areas of mud volcanoes and
natural oil seepage (Khlystov et al., 2007). Studies of isotopic composition of gases discharged at dissociation of
gas hydrates in these areas show that gas is of different genesis. Methane from the mud volcano “Malenki” is of
bacterial origin: δ 13 С(CH4) varies between -65.6‰ and -66.2‰. Gas discharged at hydrate dissociation from the
core of the mud volcano “K-2” has the following values: (δ 13 С(CH4) = -51.6 and -52.6‰, СН4/С2Н6 = 5.66;
δ 13 С(CH4) = -52‰, СН4/С2Н6 = 37.66 – 42.62). These high concentrations of ethane and rather heavy isotopic
composition are attributed to considerable amounts of gas of thermogenic genesis in sediments of the mud
volcano “K-2”.
The analysis of chemical composition of pore waters of sediments from the mud volcano “Malenki” shows that
there is a discharge of gas-saturated sulfate-calcium fluid with mineralization of up to 1700 mg/l. In the crater of
the mud volcano “K-2” there is a discharge of several fluids which differ in ionic composition and level of
mineralization: sulfate-calcium with mineralization of up to 1800 mg/l, hydrocarbonate-calcium (up to 500 mg/l)
and chloride-sodium. The concentration of these anions in pore waters in background regions is not higher than 8
and 0.4 mg/l. Methane concentrations in bottom sediments of background areas increase with depth, and
especially this abrupt rise is observed in areas of mud volcanoes. Radioactive-labeled substrates revealed high
velocities of methane oxidation and sulfate reduction not only in surface layers of bottom sediments (1-2 cm)
where there are methanotrophic bacteria, but also in the well-recovered deep layers of sediments (Klerkx et al.,
2003; Dagurova et al., 2005). High velocities of methane oxidation (0.12-4.7 ml СН4 dm -3 day -1 ) and the
abundance of aerobic methanotrophic bacteria (10 7 cell/ml, versus 10-10 4 cell/ml in background areas) are
recorded on the boundary “water-bottom sediments” in areas of mud volcanoes. Molecular microbiological
analysis shows that Baikal bacteria possess genes responsible for synthesis of methane monooxygenases which
provide methane oxidation. It is established that methanotrophic bacteria of type I prevail in Baikal bottom
sediments which have the highest homology with members of the genus Methylobacter.
The archaeal component of sediments obtained from the three sites of Lake Baikal (mud volcanoes “Malenki”
and “K-2” and the background site) has been studied with 16S rRNA gene fragment analysis. Identical
sequences of archaea have been found in sediments from mud volcanoes. They are characteristic of sediments
and GH crystals from both sites. Archaea are represented by 9 phylotypes belonging to the phylogenetic
subdivision Euryarchaeota and nine phylotypes representing Crenarchaeota. The comparison of sequences of
Baikal archaea with microorganisms which participate in anaerobic methane oxidation in marine ecosystems
shows that they belong to the same order Methanosaeta as groups ANME-1 and ANME-2. However, Baikal
sequences do not form a common cluster with them and are not identical in structure to groups from marine
ecosystems. They occupy an intermediate position on the phylogenetic tree between groups ANME-2 and
ANME-3.
This work was supported by RAS Presidium Programme 18.10, SB RAS Integration Project No. 58, and RFBR
Grant No. 08-05-00709-a.