On the Dynamics of the Southern Black Sea

The geostrophic circulation and distributions of the Cold Intermediate and the Mediterranean water masses along the Turkish coast of the Black Sea are described on the basis of hydrographic data collected during 1987–1989 surveys of the R/V Bilim. The regional circulation was found to consist of a meandering rim current conforming mainly on the topographic slope and a series of anticyclonic eddies attached to the shelf break. The eddies, observed in the period of the surveys, seem to be quasi-permanent features and are controlled by the topography and also modified by the barotropic-baroclinic instability of the flow. Further details and structural variability of the circulation were inferred by satellite imagery. The distribution of the CIL waters was found to follow the regional circulation. The characteristics of the CIL are continually modified as it is advected eastward by the rim current and partially entrapped in the anticyclonic eddies. The CIL waters are identified by core temperatures of about 6.5 °C in the Bosphorus exit region and 7.0–7.2 °C in the southeastern part of the Black Sea. The Mediterranean underflow, crossing the the southwestern Black Sea shelf region, is subject to continuous mixing due to interaction with the CIL waters. By the time the Mediterranean effluent reaches the shelf break (at depths of 100–150m), it is identified by a colder and slightly less saline water mass relative to the ambient conditions. This modified water mass then intrudes into the deeper levels of the basin in the form of patches of colder and relatively oxygen-rich water, and leads to the partial ventilation of the subhalocline waters.