WATER EXCHANGE BETWEEN MEDITERRANEAN AND BLACK SEAS DURING LATE GLACIAL-HOLOCENE: EVIDENCE FROM MARMARA AND BLACK SEAS

Chrono-stratigraphy of sediment cores from the Marmara Sea and coastal plain of the Black Sea, together with seismic stratigraphic evidence, were used to investigate the timing of water exchange between the Mediterranean and Black seas. The results show that after the last glacial period, Mediterranean waters inundated the fresh/brackish Marmara "lake" at ~12 kyr BP. The seismic, bathymetric and core data indicate that the shoreline of the Marmara "lake" prior to the transgression was at -85 m, controlled by the bedrock sill depth of the Çanakkale (Dardanelles) Strait. Oxygen isotope data of mollusks shells in the Marmara Sea show that the salinity increase during the transgression was gradual, stabilizing at ~10 kyrs BP. Comparison of the oxygen isotope data sets from the Marmara and Black seas suggests no outflow from the Black Sea to the Marmara Sea existed during 12.8-10.6 kyr BP, followed by a possible outflow during the Younger Dryas. A sapropel layer was deposited in the Marmara basin between 10.5-6.4 kyr BP. The Ba data suggest that organic productivity was generally low during deposition of the sapropel, but high during initial stages of the marine transgression, just prior to the sapropel deposition. This distribution suggests that the sapropel deposition was initiated by the marine flooding of the Marmara Sea, and not by the Black Sea outflow. Chrono-stratigraphic and seismic evidence from the Sakarya coastal plain shows that the water-level in the fresh/brackish Black Sea was at -120 m just prior to 8.1 kyr BP. The water level started rising as a result of the marine flooding via the Istanbul (Bosphorus)Strait, and reached to -27 m by ~8.1 kyr BP and -18 m by 7.2 kyr BP. The latter date represents the salinity threshold needed for the Mediterranean euryhaline mollusks to colonize the Black Sea. The Black Sea outflow appears to be persistent only after about 8 kyr BP.