ИСТИНА

One-layer and two-layer hydraulic models were used for calculations of the Black Sea level changes beginning from the Last Glacial Maximum. The longitudinal profiles of the bed of the Bosporus and Dardanelles straits and the Marmara Sea with lithological characteristics were used as the initial conditions. The entrance boundary condition was the changing discharge at the Bosporus Black Sea end, mostly from the East European Plain and the Danube basin. The exit boundary condition at the distant point of the longitudinal profile (at the Aegean Sea) was the changing oceanic level. Loose sediments from both straits were eroded by powerful flow down to the basement rock. The critical point was the altitude of the rock sill in the Dardanelles (-70 m), as that in the Bosporus was lower (-80 m). When the ocean level was lower than the sill, the level of the Black Sea was controlled by discharge from the sea through the straits and by their geometry. At the stage of maximum discharge 20.0-18.5 kyr BP (the “hydrocratic” transgression of the Black Sea) sea level reached -62 m. Later, with diminishing discharge it decreased to -66…67 m. Since 13.7 kyr BP, when the ocean level exceeded the altitude of the Dardanelles sill, the level of the Black Sea, became controlled by the ocean level and close to it. That was the stage of “eustatic” transgression. About 12 kyr BP the fresh water flow from the Black Sea through the Bosporus decreased sufficiently, so that it did not prevent the salt water intrusion from the Marmara Sea any more.