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Water-level fluctuations in the Black Sea since the Last Glacial Maximum

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Disciplines
  • Biology
  • Earth Science
  • Geography

Abstract

Two IFREMER oceanographic surveys carried out in the northwestern Black Sea in 1998 and 2002 complement previous seabed mapping and subsurface sampling by various international expeditions. They show that the lake level rose on the continental shelf to at least the -40 to -30 m isobath based on the landward limit of a Dreissena layer representative of very low salinity conditions (<5‰). The Black Sea then shows clear evidence for an onset of marine conditions at 7150 BP. From these observations, Ryan et al. (1997) concluded that the Black Sea could have filled abruptly with saltwater cascading in from the Mediterranean. Despite critical discussions of this interpretation, recent IFREMER discoveries of well preserved drowned beaches, sand dunes, and soils appear to lend support to the flood hypothesis. This new evidence includes (1) multibeam echo-sounding and seismic reflection profiles that reveal wave-cut terraces at about -100 m, (2) Romanian shelf cores that show an erosion surface indicating subaerial exposure well below the sill of the modern Bosphorus, (3) 14C ages documenting a colonization of the former terrestrial shelf surface by marine molluscs at 7150BP, (4) evidence of sea water penetration into the Black Sea in the form of recent canyon heads at the Bosphorus outlet, and (5) palynological analysis and dinocyst studies that pinpoint the arrival of freshwater during the Younger Dryas and, later, the rapid replacement of Black Sea dinocysts by a Mediterranean population.

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