Оn reasons of the long-term trends in the variability of the dissolved oxygen concentration and salinity in the area of the cold intermediate layer of the Black Sea

by

A.A. Valle, A. B. Polonsky

 Institute of Natural and Technical Systems, RF, Sevastopol, Lenin St., 28

E-mail: ogorodovaa.a@mail.ru

DOI: 10.33075/2220-5861-2023-2-07-17 

UDC 551.465 (262.5)                                                                                          

Abstract:

   In this paper, we analyzed the spatio-temporal variability of salinity and dissolved oxygen concentration based on data obtained at 50 and 75 m horizons in the area of the western and eastern gyres of the Black Sea, as well as in the area of the depth slope near the northwestern shelf. We used data on dissolved oxygen concentration and salinity from 1923 to 2020, obtained both as a result of ship observations and measured by ARGO profiler buoys, and accumulated in the data bank of the Institute of Natural and Technical Systems.

   The data were averaged over three areas: the western and eastern parts of the sea (in the vicinity of the dome-shaped isooxygen rise associated with the cyclonic circulation of the Black Sea waters, which forms two semi-closed gyres), as well as in the area of the depth slope near the northwestern shelf, where a fairly large number of measurements were made.

   The following main results were obtained in the work. An analysis of trends identified on the basis of updated archival data from 1923 to 2020 revealed an increase in salinity, as well as a decrease in the concentration of dissolved oxygen in the upper part of the main pycnocline in the centers of the western and eastern cyclonic gyres. On the periphery of the western cyclonic gyre, in the area of the depth slope near the northwestern shelf, opposite trends were noted. This difference is likely to result from an increase in the vorticity of the wind field, which leads to an intensification of circulation and an increase in the rate of vertical rising of waters in the centers of cyclonic gyres and their lowering at the periphery of these gyres.

Keywords: concentration of dissolved oxygen, salinity, long-term variability, western and eastern cyclonic gyres, depth slope.

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