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lower Crimean slope had their oxic-anoxic interfaces at approximately 120 m
and 180 m, respectively, whereas the shelf stations 038 and 055 were situated
fully in the oxic part of the water column. It has been previously observed that
the chemocline is deeper at the slope compared to the central basin (e.g. [45]
and references therein).
3.2 Sediment Methane Concentrations
Short sediment cores of up to 40 cm length were retrieved at stations 7617
and 7623 on the upper slope and at station 7605 in the central basin. Methane
concentration profiles of all three cores looked relatively similar with concen-
trations around 10 and 12 µM at the surface and decreasing values towards
the core bottom with concentrations between 4 and 8 µM (Fig. 2). The profile
shape with higher concentrations at the surface and lower concentrations at the
bottom indicates a methane flux from the top to the bottom of the core.
CH 4 [ µ M]
0
2
4
6
8
10
12
0
5
10
15
20
25
30
35
40
Figure 2. Methane concentrations in three sediment cores recovered from the NW slope (7617,
open triangles), SW slope (7623, open circles), and the central basin (7605, full circles). The
linear decrease of methane from top to bottom of the cores indicates a diffusive flux of methane
from the water column into the sediments.
3.3 Water Column Methane Concentrations
All stations except the seep station 038 showed methane concentrations of 8
to 50 nM with increasing depth in the oxic water column. At the seep station 038,
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