Das Projekt "Ventilation of Black Sea anoxic waters" wird vom Umweltbundesamt gefördert und von Universität Hamburg, Zentrum für Meeres- und Klimaforschung, Institut für Meereskunde (IfM) durchgeführt. General Information: 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 per cent 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 isopycinal 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. .. Prime Contractor: Universite de Liage, Geohydrodynamics and Environment Research Laboratory; Liage; Belgium.
Das Projekt "Turbulentes Mischen bei sehr hohen Reynoldszahlen in der Bosporus Meeresstraße" wird vom Umweltbundesamt gefördert und von Universität Erlangen-Nürnberg, Department für Chemie- und Bioingenieurwesen, Lehrstuhl für Strömungsmechanik durchgeführt. A well-defined natural turbulent shear layer flow exists between the counter-flowing currents in the two straits connecting the Marmara Sea to adjacent seas, namely the Bosphorus and Dardanelles (these domains defining the limits of the Turkish Straits System, TSS), due to the density difference between the Aegean and Black Seas. For example in the Bosphorus Strait the heavier, more salty Aegean water flows in the lower layer towards Black Sea and the lighter Black Sea water flows in the upper layer towards the Marmara Sea. These two currents generate a shear layer with almost constant velocity gradient at the middle depth of the strait with a thickness of about 10 m or larger. Within this shear layer, turbulent mixing of scalar quantities like salt and heat takes place. The Reynolds number of turbulence is expected to attain very high values (3000). As a result of very high Reynolds number, Peclet number for temperature and salinity fields are also very high in the mixing layer. The constant velocity gradient, the high Reynolds number state of the flow and the mixing of two scalars (temperature and salinity) make the Bosphorus strait a unique natural laboratory ...