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The present work represents the results of water circulation in the northern Black Sea analyzed based on the data of the surveys carried out in the 87th cruise of R/V Professor Vodyanitsky in July 2016. It is shown that during the survey the westward flows being the Rim Current (RC) manifestation are predominant within the studied water area. Based on the survey data, the latitudinal location of the Rim Current geostrophical deep stream is close to its climatic position. In the western part of the polygon, the Rim Current is divided into three branches. The northern branch is located over the shelf, the central one – over the continental slope and the southern one – over the deep-sea regions. The Sevastopol anticyclone is characterized by extremely asymmetric vertical development: its northern periphery over the shelf is weak, whereas the southern periphery over the continental slope is intensive. In the central part of the polygon the Rim Current intensifies, at that one intensive stream is traced. In the eastern part of the polygon two branches of the Rim Current are observed: the intensive northern one over the continental slope and the coastal shelf, and the one located closer to the deep-sea regions (its velocity is rather low and it weakens moving eastward). In the upper layer to the east off Cape Ai-Todor, the anticyclonic gyre is observed; whereas within the 50–100 m below it, the cyclonic turn of the currents is revealed.

The present paper represents the complex monitoring results of the hydrological field condition and water dynamics in the Black Sea northern part within the economic region of Russia carried out in the scientific expeditions in 2016 (87th, 89th and 91st cruises of R/V Professor Vodyanitsky). It is shown that distributions of all the thermohaline characteristics obtained from the data of three surveys demonstrate a pronounced seasonal character of a signal. It is manifested in consistent decrease of the upper mixed layer mean temperature, growth of temperature in the cold intermediate layer core and in deepening of the lower boundary of the upper mixed layer, the cold intermediate layer core and the hydrogen sulphide zone upper boundary. In course of three surveys, the Rim Current deep stream was located above the continental slope. The maximum velocities are observed nearby the Crimea southwestern coast. In the western part of the region considered, a well pronounced Sevastopol anticyclone (most distinct in October, 2016) is observed. The Sevastopol anticyclone manifests itself also in distributions of the hydrological characteristics. Temperature increase, salinity decrease and deepening of the lower boundary of the upper mixed layer and the cold intermediate layer core are observed on the sea surface in the anticyclone area.

A reanalysis of hydrophysical fields for 1971–1993 is used to study the formation mechanisms of the cold intermediate layer (CIL): the advective mechanism (associated with the advection of cold waters formed in the northwestern shelf (NWS)) and the convective mechanism (caused by wintertime convection inside cyclonic gyres in the central part of the sea). We consider the periods of alternating atmospheric conditions: the mild winter of 1980–1981, normal winter of 1987–1988, and cold winter of 1992–1993. Interannual features of replenishment and renewal of “old” CIL waters caused by these mechanisms are identified. In particular, cooled shelf waters sink along the continental slope and merge with “old” CIL waters during the mild winter of 1980–1981 more than 1 month later than during the cold winter 1992–1993 and more than 3 weeks later than during the normal winter of 1987–1988. The Sevastopol anticyclonic gyre and the northwest branch of the Black Sea Rim Current markedly influence the transformation of entrained cold NWS waters transported to the southwest and the central part of the water area. The local formation process of cold intermediate waters is found to be caused by the wintertime penetrating convection over domelike isosurfaces of temperature and salinity arising due to rising constant halocline (pycnocline) at the centers of cyclonic gyres because of the intensification of the wintertime circulation. Anomalously cold surface water, characterized by increased density, gradually sinks. An analysis of TS indices indicates that the transformed cold water spreads out over isopycnic surfaces with time, being entrained in cyclonic circulation and spreading throughout the sea, thus renewing “old” CIL waters.