WAS THE LAST RAPID SEA CHANGE IN THE BLACK SEA LINKED TO A CATASTROPHIC EVENT RECORDED BY MANKIND ?

Two IFREMER oceanographic surveys carried out in the Black Sea in 1998 and 2002 in the frame of European projects complement previous seabed mapping and subsurface sampling studies realised in the Black Sea by various international expeditions. Until the Ryan and Pitman theory, it was admitted that the Black Sea was predominantly a freshwater lake interrupted by possible marine invasions coincident with high sea level during the Quaternary.

From recent surveys carried out on the north-western continental shelf of the Black Sea it comes that the Black Sea's lake level rose on the shelf to at least the isobath -40 to -30 m given by the landward limit of extend of the Dreissena layer characteristic of freshwater conditions. This rise in freshwater level could coincide with the answer of the Black Sea as an important catchment basin of the melt water drained from the melting of the ice cap ensuing the Melt Water Pulse 1. It is possible that at that time the lake level filled by freshwater rose to the level of its outlet and spilled into the Mediterranean. However, in mid-Holocene at 7.5 ky BP the onset of salt water conditions are clearly evidenced in the Black Sea. From these observation Ryan et al. (1997) came to the conclusion that the Black Sea could have been filled by saltwater cascading from the Mediterranean. Even if this hypothesis have been discussed (Aksu et al., 1999, 2002), the recent discoveries of the excellent preservation of drowned beaches, sand dunes and soils during IFREMER surveys seem to bring arguments to the Ryan and Pitman assumption.

The multibeam echo-sounding and the seismic reflection profiles acquired during these 2 surveys revealed wave-cut terraces at an average water depth of -100 m. More, evidence of sea water penetration is marked at the Bosphorus outlet as the recent canyon heads mapped during the last cruise in 2002 seemed to reveal. The cores recovered on the Romanian continental shelf present an erosion surface evidencing subaerial exposure well below the level of the modern Bosphorus outlet. The 14C ages documented a simultaneous colonisation of the terrestrial surface by marine molluscs at 7.1 ky BP. Last palynology analysis and studies of the dynokysts population, precise a real onset of freshwater arrival during the Younger Dryas and abrupt replacement of Black Sea dynokyst by Mediterranean population.