Trends in Acceleration of Climate Changes in the Thermohaline Structure of the Black Sea Upper Layer

G. K. Korotaev, V. N. Belokopytov, V. L. Dorofeev✉, A. I. Mizyuk, O. S. Puzina, A. L. Kholod

Marine Hydrophysical Institute of RAS, Sevastopol, Russian Federation

✉ e-mail: dorofeyev_viktor@mail.ru

Abstract

Purpose. The purpose of the study is to assess the trends in a change of the Black Sea thermohaline structure on the interannual time scales in 2000–2020 based on three reanalyses performed using different methods, as well as direct observations.

Methods and Results. Four datasets are applied to perform the research. The first one is an array of temperature and salinity profiles on a regular grid with a 10-day time resolution and a 10′ × 15′ spatial resolution for 2000–2021, which is based on the data of 13952 oceanographic stations. The second set is formed according to the results of reanalysis carried out using the MHI Black Sea circulation model. The ERA-5 atmospheric reanalysis results are used as an atmospheric forcing. The satellite data on sea surface temperature and altimetry are assimilated in the model. The third dataset represents the reanalysis results obtained based on the NEMO model regional configuration. The atmospheric forcing is also preset using the ERA-5 reanalysis results. The following data are engaged in assimilation: the arrays of temperature and salinity profiles, and the satellite altimetry and sea surface temperature measurements. The BLKSEA_MULTIYEAR_PHY_007_004 product of the Copernicus Marine Service containing the reanalysis of daily average fields for the Black Sea basin from 01.01.1993 to 30.06.2021 constitutes the fourth set. The described four data sets have made it possible to analyze the trends in temperature and salinity changes in the upper layer of the Black Sea.

Conclusions. It is shown that since 2005, an increase in the average sea surface temperature in the Black Sea area has resulted in a tendency towards disappearance of the cold intermediate layer in its traditional understanding as a subsurface layer with a water temperature ≤ 8 °C. Besides, the accelerated sea water warming within the main pycnocline is observed. The sea haline regime in 2012–2015 is characterized by a transition from freshening to salinization of the sea surface layer that is related to a change in the external budget of fresh water, and a long-term increase in water salinity in the main pycnocline.

Keywords

retrospective analysis, Black Sea, seawater temperature, salinity, climatic changes, thermohaline structure

Acknowledgements

The observational data (array 1) and climate profiles were prepared within the framework of state assignment of FSBSI FRC MHI FNNN-2024-0014, the numerical models intended for simulations were prepared within the framework of state assignment of FSBSI FRC MHI FNNN-2024-0012, reanalysis calculations based on the MHI model (array 2) and the NEMO model (array 3) were prepared within the framework of state assignments of FSBSI FRC MHI FNNN-2023-0001) and the Ministry of Education and Science FMWE-2023-0002 of the Federal programs “Climate” and “Ecology”.

Original russian text

Original Russian Text © The Authors, 2025, published in MORSKOY GIDROFIZICHESKIY ZHURNAL, Vol. 41, Iss. 3, pp. 264–278 (2025)

For citation

Korotaev, G.K., Belokopytov, V.N., Dorofeev, V.L., Mizyuk, A.I., Puzina, O.S. and Kholod, A.L., 2025. Trends in Acceleration of Climate Changes in the Thermohaline Structure of the Black Sea Upper Layer. Physical Oceanography, 32(3), pp. 283-296.

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