Environmental Engineering Reference
In-Depth Information
Table 16.
The carbon isotope composition of the Black Sea methane.
13
C,
‰
Description of samples
δ
Reference
−
67.6
∗
1
Methane from the upper
Figure 8
Holocene sediments
−
60.4
÷−
91.0
2
Methane from cold seeps
−
65.8
Figure 9
−
62.0
÷−
72.0
−
3
Methane from bubble streams
64.5
[89]
−
58.5
÷−
68.4
4
Dissolved methane in
−
55.4
[89]
the sulfidic zone
−
50.8
÷−
58.0
5
Dissolved methane in
−
35.2
[89]
the chemocline zone
−
19.0
÷−
48.5
[88]
6
Dissolved methane in
−
54.3
[89]
the oxic zone
−
40.0
÷−
66.6
[88]
−
7
Thermogenic methane
45.7
[89]
dissolved in the sulfidic
−
÷−
43.0
47.5
zone above mud volcanoes
8
Methane from mud volcanoes
−
30.0
÷−
50.0
Table 15
∗
Numerator - the average δ
13
C;
13
C.
denominator - range of δ
13
C
average
= -45.7‰) was found at depths of
900-2070 m at station 28 around mud volcano in the central part of the western
gyre.
Using the total amount of microbial methane produced in the water column
(M
bio
=6210
10
M year
−
1
) as well as the total amount of methane oxidized
(M
tot
= 77.7 10
10
M year
−
1
), we can calculate the total production of methane
from seeps and mud volcanoes (M
sip
+M
volc
.
= 14.8 10
10
M year
−
1
) [52].
We also know δ
isotopic composition of methane (δ
13
C of methane from external sources: from cold seeps of
13
C = -65.8‰ (Table 16); from mud volcanoes of δ
13
C
volc
= -40‰ (Table
δ
13
C of biogenic methane is -67.6‰ (Table 16 No. 1), the rating value
16). Theδ
13
C of dissolved
methane (-55.4‰; Table 16, No. 3) increased by -9.1‰ (a difference in the
carbon isotope composition between methane in bubbles and anaerobically
oxidized methane) served as a basis for our calculations. We calculated the
δ
13
C of total dissolved methane (δ
13
C
tot
) is -64.5‰. The δ
of δ
13
C of external methane coming from mud volcanoes and seeps using the
isotope-mass balance:
