Environmental Engineering Reference
In-Depth Information
autotrophic methanogenesis is responsible for more than 90% of methane pro-
duction in the water column and sediments of the Black Sea [52, 72].
Figure 8.
Carbon isotopic composition of methane in sediments of the Black Sea. 1 - [40]; 2
- [2, 71]; 3 - [39]; 4 - [51].
Four methane samples studied by Hunt [40] were collected at depths of
4.8-6.3 m below the sediment surface in deep part of the Black Sea in the zone
where (as many suggest) a biogenic methane appears [5, 92]. However methane
samples analyzed by Hunt [40] had δ
13
C values typical for biogenic methane.
13
Cupto-91‰) has been recently found
in sediments of the central Black Sea [88].
Cold methane seeps discovered in 1988 during the expedition of the Institute
of Biology of the Southern Seas (Sevastopol) are active sources of methane [83].
By now, methane seeps have been discovered around the whole periphery of
the Black Sea at different depths up to 2100 m [28]. The annual flux of methane
into the water column of the western part of the Black Sea from these sources
have been estimated to be 9.8 10
10
mol. According to Dimitrov's data [26],
CH
4
emission to the atmosphere in the area of cold seeps varies from 2 to 10
10
10
mol of methane per year.
The first analysis of the isotopic composition of methane coming in the
form of bubble streams from a carbonate construction (at 226 m water depth)
gave δ
More isotopically lighter methane (δ
13
C of -58.2‰ [48], the value indicative of its microbiological origin.
We carried out extensive investigations of the isotopic composition of methane
from the Black Sea seeps in samples collected directly from vents by submarine
“Jago” during the international expedition within the framework of GOSTD-
ABS project (under the leadership of Prof. W. Michaelis, Hamburg University)
in June - July 2001. Table 14 shows the chemical composition of gases as well
as the isotopic composition of carbon and hydrogen of methane from gas seeps
[71]. A group of German participants of GOSTDABS has obtained similar to
our results. The carbon isotopic composition of methane in cold seeps varied
from -62.4 to -68.3‰ [81]. δ
13
C and δD data given in Table 14 unambigu-
