Late-Pleistocene and Holocene history of the Black Sea as indicated by stable-isotope studies

Oxygen and carbon-isotope analyses of carbonate and carbon-isotope analyses of organic matter from a 6-meter core suggest that the Black Sea was fresh or brackish between 17,000 and 9000 years ago. In the lower parts of the core the fraction of redeposited carbonate may be as high as 80%. It is possible that postdepositional exchange of oxygen isotopes in the extremely fine-grained carbonate below 1.5 meters in the core has occurred. First signs of increasing salinity in the basin can be detected in the oxygen isotopes of the carbonate that was deposited about 1500 to 2000 years prior to the onset of sapropel deposition. This interval appears to be the one between the first influx of saline Mediterranean water after the last glacial maximum and the establishment of anoxic bottom conditions in the Black Sea. The isotope data indicate a gradual rise of salinity until about 3000 years ago when the present level appears to have been reached.