A hydrological model of the Black and Caspian Seas in the late Pleistocene and early–middle Holocene

Abstract

This topic area has been a controversial one since the concept of a catastrophic Black Sea flood was first proposed, and there is still considerable disagreement between experts as to the exact sequence of events. This paper describes a numerical model of the Caspian and Black sea basins together with flows through the Manych spillway and the Bosphorus strait. The model has been calibrated against the deductions made by various researchers concerning past water levels, and parameters such as river flow volumes and evaporation rates have been assigned to give reasonable agreement with these deductions. The model successfully predicts flow through the Manych spillway during the early Khvalynian transgression of the Caspian Sea between 15.2 and 12.3 ky BP – and not thereafter. The Black Sea is predicted to reach a lowstand of −163 m in about 11 ky BP and then to fill relatively rapidly due to increased river inflow combined with a breakthrough of Mediterranean water across the Bosphorus sill in about 10.5 ky BP. This is followed by a period of high outflow through the Bosphorus and, between 9.3 and 8 ky BP, by rapidly rising salinity due to marine inflow at depth. The model also highlights two significant points of conflict with the physical evidence. These concern the lack of apparent reason for the sudden onset of sapropel formation in the Black Sea in 7.6 ky BP and the significant erosion that has apparently occurred across the Manych sill.