Counterflowing waters of the Black Sea and Mediterranean Sea are mixed by turbulent entrainment processes along their course through the Turkish Straits. In the Bosphorus Strait, the entrainment into the upper layer from below is abruptly increased when the flow is accelerated in the narrower southern reach, where the flow passes through a contraction. In contrast, the lower layer salinity decreases towards the north first by gradual entrainment within the Strait and later at an increased rate in the wide continental shelf region upon exit into the Black Sea. After passing over the sill located north of the Strait, the flow on the continental shelf proceeds in the form of a gravity current following the local slopes. The topography of the shelf region, assembled from various sources of high-resolution surveys and maps, is reminiscent of a river delta. The water properties and thickness of the Mediterranean plume is modified by turbulent entrainment, shelf currents, stratification, bottom friction and slope. The flow first spreads out on the mid-shelf slope, follows the delta features to reach the shelf edge and, finally, cascades down the steep continental slope. Horizontal spreading by convective instabilities and eastward propagation of anomalous properties along the continental slope are characteristic features of the deeper region adjacent to the shelf. The behaviour of the density current is revealed by results obtained from a reduced gravity model, suggesting that the slope and fine-scale features of the bottom topography are crucial elements in determining plume behaviour. The model results are found to be robust to environmental changes and in good correspondence with observed flow features, especially when the topography with realistic fine scales and slope are adequately represented. (C) 2001 Elsevier Science B.V. All rights reserved.