THE BLACK SEA DURING THE LAST 20.000 YEARS: SEA LEVEL, SALINITY AND CLIMATE

During the last glacial maximum the shelf zone of the Black Sea was not covered with water. The sea level was about - 130 m, the salinity very low, and there was no connection with any ocean. During the last 20.000 years the increase of sea level and salinity was continuous and not catastrophic; the climate changed periodically: Until about 14 kyr BP, there was an inflow to the Black Sea of melt water from the ice - shield of arctic and northern Europe over the drainage area of Danube, Dnjestr, Dnjepr and Don. Some of the water, mainly from the Danube, flowed along the Bulgarian coast to the Bosporus, depositing the transported sediments in a river bed parallel to the coast. Since 14 kyr BP water and sediment from the glaciers of the Alps has mainly influenced the sedimentation, as well as the outflow of water from the Black Sea to the Mediterranean. About 9.5 kyr ago the sea level of the Mediterranean reached - 34 m [1]. At this time water began to flow over the Bosporus to the Black Sea. Since then the sea level, the salinity and the sulfate content of the Black Sea have been increasing up to the present. The sea level have risen from about -20 m (7.5 kyr ago) to the present level. The salinity of the surface water has reached 17 per mil and the boundary of anoxity has risen to about -150 m. About 3450 years ago the salinity of the surface water increased to > 11 per mil and living conditions suitable for the unicell algae Emiliania huxleyi were attained. The first bloom of coccoliths took place and has been recurring with a periodicity of 11 years in connection with the 11 year sunspot cycles up to the present. A further time-marker consisting of a biomineralization process was found in a deep-sea core: framboidal greigite (clusters of Fe3S4- crystals) produced by sulfate reducing bacteria. The statistical distribution of these framboidal greigites indicates a periodic cold-warm change of the climate. A periodicity of 352 years is given by cosmic radiation from the sun via sunspot cycles over 7.000 years. The interaction between the influx of river water and Mediterranean water has influenced not only the climate but also the rise of the sea level of the Black Sea thus affecting the living conditions on its coast during the Holocene. References: [1] Aksu, A.E.et al., Marine Geol. 190 (2002), 119-149.