Purpose. The purpose of this work is to study the density of water in two ways in the suboxic layer of the Black Sea, to assess errors in calculating density using a standard method based on hydrophysical equipment data, to compare the results obtained with other characteristics of sea waters and to analyze the causes of these errors.
Methods and Results. The waters of the Black Sea suboxic layer were studied in May 2021 and October 2022. Water density was measured with a high-precision laboratory density meter and calculated from the CTD probe data using electrical conductivity by the EOS-80 equation of state. The turbidity values were measured by a turbidimeter while sampling. The concentrations of major ions of the major ion-salt composition in the studied samples were determined by a potentiometric titration, and their difference from the standard sea water IAPSO was assessed in the laboratory. The assessing procedure showed that, as compared to the standard sea water, the contents of SO42- and HCO3- were higher on average by 0.2 and 0.6%, respectively, both K+ and Ca2+ – by 0.2%, and the contents of Cl− and Na+ were lower on average by 0.4 and 0.3%, respectively. The content of Mg2+ was close to its content in standard sea water. It was found that within the range of conditional density (σt) 15.9−16.2 kg/m3, the vertical distribution of major ions was not linear, especially in relation to chlorides and sulfates.
Conclusions. As a result of determining the density of the waters of the suboxic layer of the Black Sea in two ways and comparing the obtained values, it was found that the errors in calculating the density according to the CTD probe data amount to 0.05–0.2 kg/m3 and are due to variations in the ion-salt composition and the presence of a large suspension concentrations. The density gradient measured by a density meter is approximately twice as large as that measured by a CTD probe.