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 exit region of the Bosphorus jet, and wind-stirring in winter, both contribute equally to the basin vertical mixing. The upper layer circulation of the Marmara Sea is determined from ADCP measurements and from dynamical calculations based on hydrographic data. The mean upper layer circulation is anti-cyclonic, mainly driven by the southward flowing Bosphorus jet in the enclosed domain. The Bosphorus inflow is well defined, except during the periods of low discharge in autumn and winter, when the jet becomes weaker and tends to become attached to the west coast near the exit. Mediterranean water, entering from the Dardanelles, supply the suhalocline layer. The negatively buoyant plume of well-oxygenated water is the only means of renewal of the deep waters, partially compensating for the oxygen consumed by the degradation of organic matter sinking from the upper layer into the lower layer. Yet the subhalocline 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 characteristics of the inflow density (modified in the Strait) and the weak interior stratification.