Environmental Engineering Reference
In-Depth Information
average sulphide production in the Black Sea is 30-50 Tg yr
−
1
and represents
an average annual figure, and the total sulphide inventory is about 4.6
10
3
Tg, then the residence time of hydrogen sulphide in the water column would
is about 90-150 yr. This value compares well with the water exchange rate
between oxic and anoxic layers (e.g., [82]).
Temporal variations in the average depth of the chemocline in the Black
Sea and particularly in the sulphide boundary are mainly the result of climatic
changes in the density structure of the water column. The upper anoxic boundary
location versus density for this basin has not changed over the period from 1910
to 1995 [8]. However, recent data have shown a prominent increase in sulphide
concentrations, as well as nutrient levels, within the anoxic zone (at 1000-2000
m) supposedly due to anthropogenic impact [43] or climatic variations. Future
research is needed to reveal how significant this fact or it does reflect statistical
artifacts and measurements bias.
In this review we emphasize the importance of ventilation processes in the
Black Sea anoxic zone. The sulphide budget demonstrates that the Bosporus
flux cannot be considered a main factor for deep basin ventilation. More at-
tention in future studies should be paid to near-shore mesoscale dynamics
and their influence on chemocline processes and transversal exchange between
shore and open waters [39, 76]. Severe winter conditions accompanied by
strong horizontal and vertical mixing can initiate pronounced erosion of the
pycnocline. The propagation of anticyclonic gyres along the Rim Current may
serve as an additional source of dissolved oxygen into the upper anoxic layers
(e.g., Ovchinnikov et al. [73]). Field data for the winter season are critical to
progress in our understanding of the Black Sea ecosystem. These processes are
important for the specific biogeochemical pathways within the sulphur cycle in
the Black Sea, particularly for the production of sulphur intermediate species.
The regular monitoring of mesoscale physical and chemical dynamics should
be implemented in order to understand ventilation processes in the anoxic
interior.
×
Acknowledgements
The authors wish to thank N.N. Zhabina (P.P. Shirshov Institute of Oceanol-
ogy, Moscow) for invaluable analytical help and crews of RV
Akvanavt
,
Yantar
and
Petr Kotzov
for collaboration. We are grateful to T. Ferdelman (MPI MM)
for review and editorial assistance. This work was financially supported by the
Russian Fund for Basic Research (grant 05-05-65092), Project 14.4.3. “World
Ocean” of the Russian Academy of Sciences, and Project “Black Sea” of the
Russian Ministry of Science to IIV and the German Science Foundation and
Max-Planck-Society for LLN.
