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



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.


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


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.


  1. Culkin, F. and Smed, J., 1979. The History of Standard Seawater. Oceanologica Acta, 2(3), pp. 355-364.
  2. Pawlowicz, R., 2013. Key Physical Variables in the Ocean: Temperature, Salinity, and Density. Nature Education Knowledge, 4(4), 13.
  3. Uchida, H., Kawano, T., Nakano, T., Wakita, M., Tanaka, T. and Tanihara, S., 2020. An Expanded Batch-to-Batch Correction for IAPSO Standard Seawater. Journal of Atmospheric and Oceanic Technology, 37(8), pp. 1507-1520.
  4. Pawlowicz, R., Wright, D.G. and Millero, F.J., 2011. The Effects of Biogeochemical Processes on Oceanic Conductivity/Salinity/Density Relationships and the Characterization of Real Seawater. Ocean Science, 7(3), pp. 363-387.
  5. Brewer, P.G. and Bradshaw, A., 1975. The Effect of the Non-Ideal Composition of Sea Water on Salinity and Density. Journal of Marine Research, 33(2), pp. 157-175.
  6. Millero, F.J., 2013. Chemical Oceanography. 4th Edition. Boca Raton: CRC Press, 591 p.
  7. Savenko, A.V., Savenko, V.S. and Pokrovskii, O.S., 2021. Sorption-Desorption Transformation of the Runoff of Dissolved Microelements at River-Sea Geochemical Barrier (Based on Data of Experimental Laboratory Simulation). Water Resources, 48(2), pp. 285-290.
  8. Ivanov, V.A. and Belokopytov, V.N., 2013. Oceanography of Black Sea. Sevastopol: ECOSI-Gidrofizika, 210 p.
  9. Hiscock, W.T. and Millero, F.J., 2006. Alkalinity of the Anoxic Waters in the Western Black Sea. Deep Sea Research Part II: Topical Studies in Oceanography, 53(17-19), pp. 1787-1801.
  10. Vinogradov, M.E. and Nalbandov, Y.R., 1990. Influence of Water Density Variations on the Distribution of the Physical, Chemical and Biological Characteristics of the Open Regions of the Black Sea. Oceanology, 30(5), pp. 769-777 (in Russian).
  11. Zatsepin, A.G., Ostrovskii, A.G., Kremenetskiy, V.V., Piotukh, V.B., Kuklev, S.B., Moskalenko, L.V., Podymov, O.I., Baranov, V.I., Korzh, A.O. [et al.], 2013. On the Nature of Short-Period Oscillations of the Main Black Sea Pycnocline, Submesoscale Eddies, and Response of the Marine Environment to the Catastrophic Shower of 2012. Izvestiya, Atmospheric and Oceanic Physics, 49(6), pp. 659-673.
  12. Konovalov, S.K., Vidnichuk, A.V. and Orekhova, N.A., 2018. Spatio-Temporal Characteristics of the Hydrochemical Structure of Water in the Deep-Sea Part of the Black Sea. In: A. P. Lisitzin, ed., 2018. The Black Sea System. Moscow: Scientific World, pp. 106-119. (in Russian).
  13. Murray, J.W., Jannasch, H.W., Honjo, S., Anderson, R.F., Reeburgh, W.S., Top, Z., Friederich, G.E., Codispoti, L.A. and Izdar, E., 1989. Unexpected Changes in the Oxic/Anoxic Interface in the Black Sea. Nature, 338(6214), pp. 411-413.
  14. Kirkpatrick, J.B., Fuchsman, C.A., Yakushev, E.V., Staley, J.T. and Murray, J.W., 2012. Concurrent Activity of Anammox and Denitrifying Bacteria in the Black Sea. Frontiers in Microbiology, 3, 256.
  15. Dubinin, A.V., Dubinina, E.O., Kossova, S.A. and Berezhnaya, E.D., 2017. Ventilation of the Black Sea Anoxic Zone: Evidence from the Sulfur Isotope Composition of Sulfate. Doklady Earth Sciences, 475(2), pp. 877-882.
  16. Volkov, I.I., Kontar, E.A., Lukashev, Yu.F., Neretin, L.N., Nyffeler, F. and Rozanov, A.G., 1997. Upper Boundary of Hydrogen Sulfide: Implications for the Nepheloid Redox Layer in Waters of the Caucasian Slope of the Black Sea. Geochemistry International, 35, pp. 540-550.
  17. Yilmaz, A., Coban-Yildiz, Y., Telli-Karakos, F. and Bologa, A., 2006. Surface and Mid-Water Sources of Organic Carbon by Photoautotrophic and Chemoautotrophic Production in the Black Sea. Deep Sea Research Part II: Topical Studies in Oceanography, 53(17-19), pp. 1988-2004.
  18. Kremling, K., 1974. Relation between Chlorinity and Conductometric Salinity in Black Sea Water. In: E. T. Degens and D. A. Ross, 1974. The Black Sea – Geology, Chemistry, and Biology. Tulsa, USA: American Association of Petroleum Geologists, pp. 151-154.
  19. Gershanovich, D.E., Ryabinin, A.I. and Simonov, A.I., eds., 1992. Hydrometeorology and Hydrochemistry of Seas in the USSR. Vol. 4. The Black Sea. Issue 2. Hydrochemical Conditions and Oceanological Basis for the Formation of Biological Productivity. Saint Petersburg: Gidrometeoizdat, 220 p. (in Russian).
  20. Pawlowicz, R., 2010. A Model for Predicting Changes in the Electrical Conductivity, Practical Salinity, and Absolute Salinity of Seawater due to Variations in Relative Chemical Composition. Ocean Science, 6(1), pp. 361-378.
  21. Andrulionis, N.Yu. and Zavyalov, P.O., 2019. Laboratory Studies of the Main Component Composition of Hypergaline Lakes. Physical Oceanography, 26(1), pp. 13-31.
  22. Millero, F.J., 2010. History of the Equation of State of Seawater. Oceanography, 23(3), pp. 18-33.
  23. Millero, F.J. and Huang, F., 2009. The Density of Seawater as a Function of Salinity (5 to 70 g kg−1) and Temperature (273.15 to 363.15 K). Ocean Science, 5(2), pp. 91-100.
  24. Kayukawa, Y. and Uchida, H., 2021. Absolute Density Measurements for Standard Sea-Water by Hydrostatic Weighing of Silicon Sinker. Measurement: Sensors, 18, 100200.
  25. Khoruzhii, D.S., Ovsyanyi, E.I. and Konovalov, S.K., 2011. Comparison of the Results of Determination of the Carbonate System and the Total Alkalinity of Seawater According to the Data Obtained by Using Different Analytic Methods. Physical Oceanography, 21(3), pp. 182-194.
  26. Kremling, K., 1999. Determination of the Major Constituents. In: K. Grasshoff, K. Kremling and M. Ehrhardt, eds., 1999. Methods of Seawater Analysis. Weinheim: WILEY-VCH. Chapter 11, pp. 229-251.
  27. Millero, F.J., Feistel, R., Wright, D.G. and McDougall, T.J., 2008. The Composition of Standard Seawater and the Definition of the Reference-Composition Salinity Scale. Deep Sea Research Part I: Oceanographic Research Papers, 55(1), pp. 50-72.
  28. McDougall, T.J., Jackett, D.R., Millero, F.J., Pawlowicz, R. and Barker, P.M., 2012. An Algorithm for Estimating Absolute Salinity in the Global Ocean. Ocean Science, 8(6), pp. 1123-1134.
  29. Sauerheber, R. and Heinz, B., 2015. Temperature Effects on Conductivity of Seawater and Physiologic Saline, Mechanism and Significance. Chemical Sciences Journal, 6(4), 1000109.
  30. Stunzhas, P.A. and Yakushev, E.V., 2006. Fine Hydrochemical Structure of the Redox Zone in the Black Sea According to the Results of Measurements with an Open Oxygen Sensor and with Bottle Samplers. Oceanology, 46(5), pp. 629-641.
  31. Andrulionis, N.Yu., Zavialov, I.B. and Rozhdestvenskiy, S.A., 2024. Major Ion Composition of Waters in the Kerch Strait and the Adjacent Areas. Physical Oceanography, 31(1), pp. 79-98.

Download the article (PDF)