The Black Sea basin filling by the Mediterranean salt water during the Holocene

The origin of the bottom counterflow in Bosphorus Strait during the early Holocene, its temporal development and the Black Sea filling by the Mediterranean salt water is discussed in this paper. At 10 ka, the depth of the strait was 10 m, the velocity of accumulation body growth in the southern part of the strait was 3 mm/year, and the velocity of the ocean transgression was 13.5 mm/year. The freshwater balance of the Black Sea is accepted as it is now. Based on mathematical modeling the bottom counterflow breakthrough occurred when the depth of the strait was 16.5 m, at about 9400 years ago. Before this, salt water penetrated into the Black Sea in the autumn-winter seasons during short periods of time, when the Bosphorus upper stream was absent. The Navier–Stokes equations were used to describe the water circulation. Temporal dependencies of the counterflow depth, water discharge in counterflow and depth of the halocline in the Black Sea was calculated.The halocline reached the depth of 100 m about 7200 years ago, and a situation close to present one (the lower Bosphorus flow brought salt into the Black Sea, with the upper stream returning it to the Sea of Marmara. The water discharge in the low water layer was insignificant during the time interval from 9400 to 8400 years ago. Then, it quickly rose to about 700 km3/year.