Errors in Calculating Density Using the CTD probe data in Suboxic Layer of the Black Sea

N. Yu. Andrulionis✉, O. I. Podymov

P. P. Shirshov Institute of Oceanology of RAS, Moscow, Russian Federation

✉ e-mail: natalya@ocean.ru

Abstract

Purpose. The purpose of this work is to study the density of water in two ways in the suboxiс 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 suboxiс 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 SO2-4 and HCO-3 were higher on average by 0.2 and 0.6%, respectively, both K+ and Ca2+ – by 0.2%, and the contents of Сl- 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 suboxiс 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.

Keywords

Black Sea, suboxiс layer, water density, water salinity, density measurement, CTD sounding, hydrochemical characteristics of water, ionic composition

Acknowledgements

The research was carried out with the support of Ministry of Education and Science of Russian Federation, Agreement No. 07-15-2021-941. The authors are grateful to Senior Researcher of Andreyev Acoustics Institute and Chief Specialist of IO RAS V. A. Soloviev for his assistance in studies and preparation of the paper.

Original russian text

Original Russian Text © N. Yu. Andrulionis, O. I. Podymov, 2024, published in MORSKOY GIDROFIZICHESKIY ZHURNAL, Vol. 40, Iss. 3, pp. 371–385 (2024)

For citation

Andrulionis, N.Yu. and Podymov, O.I., 2024. Errors in Calculating Density Using the CTD probe data in Suboxic Layer of the Black Sea. Physical Oceanography, 31(3), pp. 336-349.

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