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Ventilation of Black Sea anoxic waters

Objective


Foreseen Results

The objectives of this research are to combine years of observational data available in the participating laboratories with existing and presently developed models of increasing complexity to study various regimes of convection/advection/diffusion processes in the Black Sea with emphasis on their combined effects on transport and retention of pollutants, and the renewal of basin waters.
The Black Sea is practically an enclosed sea with restricted exchange through the Bosphorus Strait. As a result, a strong permanent pycnocline (halocline) develops and prevents deep ventilation in the basin interior. These restrictions are responsible for anoxia in 87 % of its volume. For all the Black Sea riparian countries, shoaling the oxic/anoxic interface which might occur as a response to decrease in fresh water input due to intensive irrigation projects in the Former Soviet Union (Murray et al., 1989) might have a catastrophic effect. Recent data reveal a remarkable stability of the oxic/anoxic interface and of the chemocline in terms of isopycnal co-ordinates on a long term scale. However, our understanding of the real reasons for such stability is poor and, furthermore, a considerable variability of the Black Sea pycnocline structure has also been revealed by recent basin wide surveys showing variations in the intensity of the pycnocline ventilation on a decadal time scale.

Also, in recent decades, devasting alterations in the ecosystem of the Black Sea have been registered. These changes occurred partly due to eutrophication. The last phenomenon, being a response to anthropogenic inputs for the shelf area, is closely related to intensity of the ventilation within the upper pycnocline for the open part of the sea. The Black Sea pycnocline is ventilated either due to rather slow vertical diffusion or through lateral injection of dense Marmara Sea water, coming with Bosphorus inflow, mixed with oxygenated water of the Cold Intermediate Layer.

In this study, which is complementing to other on-going studies, attention will be given to :
(i)the effects of the Mediterranean Water coming out of the Bosphorus (dynamics, topographical control, mixing and spreading on the shelf, and cascading along the continental slope, intrusion and spreading into the basin interior);
1- Cold Intermediate Water (CIW) formation (shallow convention processes on the shelf, trapping and dynamical controls by shelf topography, three dimensional and meso-scale effects and interaction with rim current and eddies) and resulting transport of sediment and radioactive pollutants from shelf regions to the interior and abyssal regions with gravity currants, remobilization of pollutants, and contribution to overall sedimentation processes;
2- controls of the stratification and material exchange across the main pycnoline (the role of CIW formation and the inflow of Mediterranean water including shelf and entrainment processes on the vertical exchange of water, nutrients, hydrogen sulphide, oxygen and other radioactive contaminants; short and long term climatic control and influences on the ventilation); assessment description and understanding of the Black Sea chemocline peculiar structure and variability.

Coordinator

Université de Liège
Address
85,
4000 Liège
Belgium

Participants (4)

MARINE HYDROPHYSICAL INSTITUTE - UKRAINIAN NATIONAL ACADEMY OF SCIENCE
Ukraine
Address
2,Kapitanskaya Street 2
335000 Sevastopol
P.P.SHIRSHOV INSTITUTE OF OCEANOLOGY - RUSSIAN ACADEMY OF SCIENCES
Russia
Address
23,Nakhimovsky Ave. 36
117851 Moscow
UNIVERSITY OF HAMBURG
Germany
Address
Troplowitzstrasse 7
22529 Hamburg
University of Sofia Kliment Ohridski
Bulgaria
Address
5,James Bourchier Street
1126 Sofia