ON CHANGES IN THE HYDROPHYSICAL AND HYDROCHEMICAL STRUCTURE OF THE UPPER 200 m LAYER OF THE BLACK SEA IN THE LAST DECADE AND A HALF

According to the long-term monitoring of the north-eastern part of the Black Sea at the Gelendzhik testing site of the IO RAS, a trend of salinization and warming of the surface waters of the Black Sea has been observed in the last 15 years. As a result, the increase in salinity of the surface water layer over these years is approximately 0.5 PSU and temperature - by 0.5 °C. At the same time, the density of water in the upper 300 m layer increases, which is expressed in an increase in isopycnals and a decrease in their depth. It was found that in the period 2014–2024, the depth of the redox interface did not change and in the observation area amounted to 156 ± 9 m, while the values of the potential density at which hydrogen sulfide appears changed from 16.15 ± 0.02 to 16.25 ± 0.02 kg/m³. It follows that the generally accepted binding of the appearance and disappearance of hydrochemical parameters to certain values of water density cannot be considered absolute and changes over time. In the conditions of the revealed salinization and warming of the active layer of Black Sea waters in the last 15 years, the distribution of oxygen and hydrogen sulfide by depth can be considered as more stable characteristics, less susceptible to climate change, at least during the observation period of 2014–2024 described in the article.