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

Abstract

The surface circulation of the Marmara Sea was studied with satellite-tracked drifers during 2 feld experiments. A total of29 drifers were released in September 2008 and February 2009 at key locations south of the Bosphorus and in the central part of thesea. Te spatial structures and temporal variability are described together with the atmospheric conditions of the Marmara Sea duringthe period of study. The behavior of drifers with respect to the wind was qualitatively analyzed. The pseudo-Eulerian velocity statisticswere computed from the interpolated positions and maps of the mean currents were produced using the data sorted by experiment.The results are the frst of their kind in the area and complement previous fndings obtained by means of hydrographic and ADCPmeasurements. Te overall surface fow is westward oriented from the Bosphorus Strait to the Dardanelles Strait. A jet-like fow thatenters the Marmara Sea from the Bosphorus Strait and, meandering, crosses the sea prevailed during the entire study period. Te surfacecirculation of the Marmara Sea is quite complex and displays very high variability. For example, the drifer data reveal that during thestudy period the mean fow was confned immediately north of Marmara Island in the western part of the sea. Tis was due to thepresence of a large anticyclone in the northwestern area of the sea that had never been observed before. Additionally, sudden reversalsand a complex eddy activity (mainly anticyclonic) were observed. Wind plays an important role in the surface circulation. Te upperlayer currents seem to respond very rapidly to the direct and indirect efect of the wind forcing.