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Oceanographic surveys in the Black Sea during 1998, 2002, and 2004 in the framework of a French-Romanian joint project, and recently in the framework of the European project ASSEMBLAGE, complement previous seabed mapping and subsurface sampling studies undertaken in the Black Sea by various international expeditions. Until the Ryan and Pitman flood theory and prior to this project, it was proposed that the Black Sea was predominantly a fresh-water lake interrupted by possible marine invasions coincident with high sea level during the Quaternary.

From the recent surveys carried out on the western part of the Black Sea it is evident that the Black Sea's lake level rose on the shelf to at least the isobath −40 to −30 m as ascertained by the landward limit of extent of the Dreissena layer characteristic of brackish to fresh-water conditions. This rise in the lake level could coincide with the answer of the Black Sea catchment's basin to the meltwater drained from the thawing of the ice cap ensuing Melt Water Pulse 1A (Bard et al., 1996). It is possible that at that time the lake level filled by fresh water reached the level of its outlet and spilled into the Mediterranean Sea. Later, in the mid-Holocene at 7.5 k.y. B.P., the onset of salt-water conditions is clearly evident in the Black Sea. From these observations Ryan et al. (1997) came to the conclusion that the Black Sea could have been filled by salt water cascading from the Mediterranean. Even though this hypothesis has been challenged (Aksu et al., 2002b, 1999b), the recent confirmation of the excellent preservation of drowned beaches, sand dunes, and soils during Ifremer (Institut français de recherche pour l'exploitation de la mer) surveys seems to support the Ryan and Pitman hypothesis (Ryan and Pitman, 1999).

The multibeam echo-sounding and the seismic reflection profiles acquired on the Romanian margin during our surveys revealed wave-cut terraces at an average water depth of 100 m. More evidence of seawater penetration is marked at the Bosphorus outlet by the presence of recent canyon heads mapped during the last cruise in 2002. The cores recovered on the Romanian continental shelf penetrated an erosion surface, indicating subaerial exposure well below the level of the modern Bosphorus outlet. The 14C ages documented a simultaneous colonization of the terrestrial surface by marine mollusks at 7.1 k.y. B.P. The most recent palynology analysis and studies of the dynocyst population (Popescu, 2004) document a real onset of fresh-water arrival during the Younger Dryas and abrupt replacement of Black Sea dynocyst by Mediterranean population, coincident with the onset of the marine mollusks.

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