Purpose. The work is purposed at studying the changes in distribution of water thermohaline characteristics in the main pycnocline and below (100–400 m) in the northern and northeastern parts of the Black Sea.
Methods and Results. The data of hydrological measurements (conductivity, temperature and depth) obtained by the scientists of Marine Hydrophysical Institute, RAS in the 20 cruises of R/V "Professor Vodyanitsky" in the northern and northeastern parts of the Black Sea in 2016–2021 were used. A gradual increase in water temperature and salinity below the main pycnocline was revealed; it extended up to the 16.9 kg/m3 (~ 370 m) isopycne. For the indicated period, the warming constituted 0.14 °C for isopycne 16.3 kg/m3 (~ 150 m), 0.09 °C for isopycne 16.5 kg/m3 (~ 180 m), and 0.02 °C for isopycne 16.9 kg/m3 (~ 370 m). During the same period, the salinity increase within the range of isopycnes 15.9–16.1 kg/m3 amounted to 0.03 PSU. The changes in temperature and salinity have resulted in the rise of isopycnic surfaces. The 15.8 kg/m3 isopycne rose from the 106 m horizon in 2016 to the 96 m one in 2021, and the 16.1 kg/m3 isopycne – from the 126 m horizon to the 115 m one. The rates of isopycne rises within the range 15.8–16.3 kg/m3 were maximum and amounted to 3–3.5 m/year.
Conclusions. In the last decade, the trends in increasing temperature and salinity in the upper 200–300 m layer are typical of the whole Black Sea area. Besides, this phenomenon is observed much deeper, up to the ~ 400 m depth. The intensity of warming decreases with depth. A comparison with the data from earlier measurements has shown that just during the indicated period, significant changes, particularly evident since 2018, took place. In general, the changes observed in the Black Sea thermohaline structure below the main pycnocline can be induced by the climatic changes, as well as by the increased inflow of the Mediterranean Sea waters (also transformed due to general climate warming) through the Bosphorus Strait.