On the surface circulation of the Marmara Sea as deduced from drifters

The surface circulation of the Marmara Sea was studied with satellite-tracked drifters during 2 field experiments. A total of 29 drifters were released in September 2008 and February 2009 at key locations south of the Bosphorus and in the central part of the sea. The spatial structures and temporal variability are described together with the atmospheric conditions of the Marmara Sea during the period of study. The behavior of drifters with respect to the wind was qualitatively analyzed. The pseudo-Eulerian velocity statistics were computed from the interpolated positions and maps of the mean currents were produced using the data sorted by experiment. The results are the first of their kind in the area and complement previous findings obtained by means of hydrographic and ADCP measurements. The overall surface flow is westward oriented from the Bosphorus Strait to the Dardanelles Strait. A jet-like flow that enters the Marmara Sea from the Bosphorus Strait and, meandering, crosses the sea prevailed during the entire study period. The surface circulation of the Marmara Sea is quite complex and displays very high variability. For example, the drifter data reveal that during the study period the mean flow was confined immediately north of Marmara Island in the western part of the sea. This was due to the presence of a large anticyclone in the northwestern area of the sea that had never been observed before. Additionally, sudden reversals and a complex eddy activity (mainly anticyclonic) were observed. Wind plays an important role in the surface circulation. The upper layer currents seem to respond very rapidly to the direct and indirect effect of the wind forcing.