Environmental Engineering Reference
In-Depth Information
methane reached 10 times higher values of up to 550 nM above the seep (Fig.
3). Below the chemocline at most stations methane values increased rapidly to
approximately 10 µM at about 500 m, and remained stable around 10.5 to 11.3
µM from 500 to 2100 m water depth. Exceptions were the upper slope stations
in the North-West (7617) where methane concentrations increased from 0.4
to 2.7 µM from 150 to 295 m, and in the South-West (7623), where methane
concentrations increased from 0.5 at 150 m to 4.5 µM at 340 m (Fig. 4). The
water columns sampled at the lower slope position (064 and 072) showed very
similar concentration profiles with maximum values of 12.5 µM (Fig. 5).
13
CH
4
[nM]
CH
4
(per mil)
δ
0
200
400
600
800
-70
-60
-50
-40
0
0
20
20
40
40
60
60
80
80
100
100
Figure 3.
Water column methane concentrations (nM) at the seep 038 (full circles) and
reference site 055 (open circles) located on the north-western shelf of the Black Sea. Carbon
isotopic composition (δ
13
C
CH
4
vs. VPDB) of the dissolved methane from the water column
above the seep site (038, full squares) and reference site (055, open squares).
3.4 Isotopic Composition of Water Column Methane
The stable carbon isotopic composition of methane was measured at the
north-western station (7617), the central station (7605), at the lower slope
station (064), and at the two shelf stations (038, seep and 055, reference, Fig.
4,5,3). At the central station (7605, Fig. 4) δ
13
C
CH
4
values in the anoxic deep
water varied around - 54 ‰ and the shallowest sample taken at 30 m water
depth had aδ
13
C
CH
4
value of -42 ‰. A striking change in isotope fractionation
