The Near Bottom Hypoxia and Hydrogen Sulphide Formation on the Black Sea Shelf

Abstract

Purpose. Estimation of the Northwestern part of the Black Sea Shelf in modern period. Methods. The sample of average daily measurements of the temperature, salinity on the surface, level, wind velocity and direction during 2007, 2012 and 2017 had been done. The analyses of the cruise investigation parameters and NASA satellite photos had been done in this region as well. Results. Increasing of nutrient, heavy metals, oil concentration in the Danube, Dnieper and Dniester of water runoff was fixed during the last 50 years. It was the reason of its permanent accumulation in marine ecosystem. Also it was the reason of anthropogenic eutrophication development in the sea water in spring and at the beginning of summer time. Later, at the end of summer and in autumn the dissolved oxygen is decreasing in the bottom layers because of destruction of organic matter. In the last years, decreasing of nutrient from the rivers input was marked. It provided the increasing the transparency in the sea column and made the water condition more positive. But for assessment of the whole ecosystem state the complexes monitoring is absolutely necessary. In September of 2017 the special investigation cruise was done. The result shown the deficit of the dissolved oxygen – hypoxia in the near bottom layer is spreading in the center of the shelf ecosystem (the depths are more than 20 m). The oxygen concentrations were less than 2,0 ml/l.. The reason of this negative phenomena was provided by NASA satellite photos of eutrophication process in summer and marking of upwelling at the shallow waters during the warm period in 2007, 2012 and 2017. Conclusions. Anthropogenic eutrophication development in the sea water was fixed as well as the near bottom hypoxia and hydrogen sulphide formation in the Ukrainian part of the Northwestern shelf of the Black sea in the modern period. Spatial scale of this phenomena is comparable with the scales from 70's of last century.