THE CIRCULATION AND HYDROGRAPHY OF THE MARMARA SEA

A comprehensive set of data collected during 1986-1992 reveal seasonal and interannual variability in the circulation and hydrography of the Marmara Sea. Waters, which have contrasting properties and originate from the adjacent basins, supply the two-layer stratified flows in the Sea of Marmara. Turbulent entrainment into the upper layer in the exi t region of the Bosphorus jet, and wind-stirring in winter, both contr ibute equally to the basin vertical mixing. The upper layer circulatio n of the Marmara Sea is determined from ADCP measurements and from dyn amical calculations based on hydrographic data. The mean upper layer c irculation is anti-cyclonic, mainly driven by the southward flowing Bo sphorus jet in the enclosed domain. The Bosphorus inflow is well defin ed, except during the periods of low discharge in autumn and winter, w hen the jet becomes weaker and tends to become attached to the west co ast near the exit. Mediterranean waters, entering from the Dardanelles , supply the suhalocline layer. The negatively buoyant plume of well-o xygenated water is the only means of renewal of the deep waters, parti ally compensating for the oxygen consumed by the degradation of organi c matter sinking from the upper layer into the lower layer. Yet the su bhalocline waters remain permanently deficient in oxygen, as a result of the internal balances of diffusion, advection and consumption. The depth to which the plume penetrates is a function of the seasonal char acteristics of the inflow density (modified in the Strait) and the wea k interior stratification.