Environmental Engineering Reference
In-Depth Information
water column, but also the H
2
S spatial field. H
2
S boundary deepens 10-20 m
in the centers of these structures compared to the adjacent waters (Fig. 8B).
The isopycnal analysis of the H
2
S distribution on several transects across the
coastal zone show that an intensified exchange between oxic and anoxic wa-
ters may happen down to 500 m in the convergence zone between the MRC
and propagating anticyclonic gyres [61]. Such mesoscale mixing processes
can significantly enhance sulphide oxidation at the interface and contribute in
ventilation of the anoxic zone as a whole. The difference between the sulphur
isotopic composition of sulfate and sulphide is about 60 ‰ in the anoxic zone
of the Black Sea. Neretin et al. [63] hypothesized that a combination of very
low sulfate reduction rates throughout most of the water column (
<<
1nMd
−
1
,
[3]) and efficient mixing mechanisms below the chemocline producing sulphur
intermediates are the factors that cause high isotope depletion in sulphide. A
range of physical processes such as intensified winter mixing and coastal dy-
namics together with oxygen intrusions carried by the modified Mediterranean
Water may facilitate the formation and transport of intermediate sulphur species
into the anoxic interior.
A
B
Figure 9.
Geostrophic circulation [73] (A) and topography of the H
2
S upper boundary [61]
(B) in the north-eastern part of the Black Sea in September 1994; NAE stands for nearshore anti-
cyclonic eddy, CE stands for cyclonic eddy.
6. “IRREGULAR” VERTICAL SULPHIDE
DISTRIBUTIONS CAUSED BY LATERAL OXYGEN
INTRUSIONS
Overall, the average H
2
S vertical profiles look rather similar over the entire
Black Sea area. However, there are exceptions caused by intense perturbations
to the hydrodynamics along the Main Rim Current. Such an 'irregular' H
2
S
vertical distribution has been observed in the water column in the area adjacent
to Sakarya Canyon (Fig. 8). Results of the RV “Bilim” expedition conclusively
