RESULTS OF MARINE SCIENTIFIC RESEARCH OF THE SOUTHERN SCIENTIFIC CENTRE OF THE RUSSIAN ACADEMY OF SCIENCES (SSC RAS) IN THE SEA OF AZOV IN 2003-2018 PART 1: HYDROLOGY AND HYDROCHEMISTRY
The results of analysis of long-term expeditionary research of the SSC RAS (the Southern Scientific Centre of the Russian Academy of Sciences), focused on the Sea of Azov and the oceanographic database of the SSC RAS (thermohaline structure, water transparency, hydrochemical parameters) are summarized and presented. It is noted that the distribution of isotherms on maps dated 1962-2008 shows an increase in the area of “warm” fields for the winter and spring seasons and an increase in the area of “cold” fields for the autumn one. The same trend is also maintained when comparing annual water temperature curves for the Taganrog Bay and the central part of the sea. The long-term average annual vertical oceanographic sections along the line running through the deepest part of the Sea of Azov from the mouth of the Don River to the Kerch Strait with a total length of 350 km are presented. It is noted that, under conditions of unsteady runoff, a change in frontogenesis occurs in the Taganrog Bay. Thus, an increase in the flow of the Don River in 2018 up to the level typical for the period 2001- 2005 led to the intensified formation of fronts in the Taganrog Bay. The water salinity throughout the bay has decreased, however, the values of the maxima in the western and eastern regions increased. The cases of inflow of the waters with higher salinity into the mouth of the seashore and into the arms of the Don Delta are recorded. Based on the information concerning Secchi disk depth (the depth of visibility of a white disk), which characterizes the relative transparency of water, four main types of seasonal variability of relative transparency of the Azov waters were identified, and all four types were found out to have similar features with phytoplankton dynamics. On the basis of the expeditionary observations of the SSC RAS in 2007-2018, seasonal dynamics and spatial differences in the concentrations of dissolved organic carbon in the waters of the Lower Don, the Taganrog Bay, the Sea of Azov and the northeastern part of the Black Sea are shown. It is noted that high values and increased variability of concentrations of organic carbon from the Don and Azov waters are the result of intrabasin life processes, including intensive production of microalgae, their consumption by consumers, and active bacterial processing of dead organisms with accumulation of organic matter in the water.