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Studies of Black Sea cetaceans were carried out in September 2018 (11 days, 799 km of the survey route) and June 2019 (12 days, 1174 km of the survey route). The research vessel followed a survey route off the Caucasian coast of the Black Sea from Anapa to Adler at a distance of up to 165 km from the coast. There were 103 sightings of cetaceans (548 individuals) in 2018 and 347 sightings (1280 individuals) in 2019. Three species were recorded: common dolphin, bottlenose dolphin, and harbor porpoise; their ratios were 78.1 : 20.8 : 1.1 in 2018 and 90.1 : 7.1 : 2.8 in 2019. Common dolphins were sighted everywhere; in June, they were encountered more frequently in the coastal water area; in September, in the open sea. This was probably preconditioned by the availability of prey. Bottlenose dolphins and harbor porpoises performed short-distance seasonal migrations and preferred to remain in local coastal habitats.

Results of the study of water exchange between the Azov and Black seas based on the data of contact measurements in 2019 are presented. Estimates of the scale of the Sea of Azov plume were obtained under conditions of a strong northeasterly wind (9–10 m/s). The results of field measurements confirmed the determining role of wind in water exchange through the Kerch Strait, which made it possible to form statistics on the flow of the Sea of Azov waters into the Black Sea based on wind reanalysis data over the past twenty years. A new method for calculating the flow of the Sea of Azov water through the Kerch Strait based on the comparison of satellite and field data is proposed and applied. The calculation of the Sea of Azov water transport is generally based on the assessment of the spatial characteristics of the Sea of Azov plume in the Black Sea and, in particular, on the determination of the dependence of its area on wind parameters. The average annual transport of the Sea of Azov water estimated using the new method practically coincides with the average value of all estimates of water exchange through the Kerch Strait, obtained using other calculation methods. We also considered the reverse case of the inflow of the Black Sea waters into the Sea of Azov after the end of the period of intense flow of the Sea of Azov waters into the Black Sea.

The water exchange between the Black Sea and the Azov Sea is investigated on the base of the marine observations aboard the R/V Deneb in 2018 and 2019. The surveys were conducted under different weather conditions, which led to large variability of the results. The northern wind contributes to the formation of water transfer to the south, which exceeds by five to six times the water transfer to the north; the southern wind leads to filling of the entire cross-section, 17 km wide, with waters flowing northward and a volume up to 30 times higher than the average flow rate of the Don River for the modern low-water period. In this study, the water circulation patterns of the Azov Sea on the surface and in the bottom layers were constructed, confirming the drift scheme of water movement. Inflows of Black Sea water to Temryuk Bay are described in detail. The classification of types of water stratification in Temryuk Bay was based on data from the Southern Scientific Center, Russian Academy of Sciences; four types have been distinguished, and restructuring of the types of stratification in relation to the sea salinization is observed.

A criterion or index for assessing the hazard of storm-induced coastal erosion is suggested. It is based on comparison of actual beach volume $$~{{V}_{b}}$$ and its optimal value $${{V}_{{b^{*}}}}$$ sufficient to avoid irreversible beach changes due to severest storm attack over the year. The erosion hazard level is determined taking into account the difference of $$~{{V}_{b}}$$ and $${{V}_{{b^{*}}}}$$ ; it reaches the maximum (3 points) when the actual beach volume becomes less than a half the optimal value (0 points corresponds to $$~{{V}_{b}}$$ > $${{V}_{{b^{*}}}}$$ ). To calculate the erosion index, a representative beach profile is required, as well as the data on the mean sand size and wind/wave regime. The erosion index is tested on the coasts of the Anapa bay-bar (Black Sea) and southern part of the Vistula Spit (Baltic Sea). The index makes it possible distinguish vulnerable sections of the coast, and at the same time it reflects the sediment deficit volume that could be used in shore protection designs.

—The article considers the modern dynamics of Bakalskaya Spit (northwestern Crimea), the distal part of which separated in 2010, becoming an island. It is shown that in the last 200 years, the coastline to its east and west has retreated. Analysis of satellite data and geodetic surveys revealed that in the last 30 years, the distal part of the spit shifted northeast by 300 m and the western branch of the spit shifted east by 160 m. After separation of Peschany Island, its area was 0.56 km2; by 2018, it had contracted to 0.31 km2. The width of the strait that formed is about 1 km. It has been suggested that an increase in storm activity and an abnormally high Black Sea level in the previous period led to formation of the island under decreased sediment influx conditions.

The article describes a technique for studying the spatiotemporal variability of the temperature of the water medium in the Black Sea shelf zone using a cluster of anchored temperature sensor chains (thermoresister chains). The cluster consists of three spaced thermoresister chains situated on the inner shelf of the northeastern Black Sea and operating as a part of the Gelendzhik Site of the Shirshov Institute of Oceanology, Russian Academy of Sciences (IO RAS). It is shown that the cluster makes it possible to effectively record the short-period spatiotemporal variability of the temperature field. The quantitative characteristics of this variability, as well as external factors determining it, are established. One of the factors is internal waves. The temperature variability can be used to determine the fluctuation amplitude, and recording these fluctuations at spaced thermoresistor chains makes it possible to find the velocity and propagation direction of internal waves. Some examples of recording trains of short-period internal waves are presented. Different methods are used to visualize the temporal variability of the vertical temperature distribution.

The coast of the shallow Azov Sea is characterized by a series of sand spits. Based on the results of drilling conducted on Dolgaya Spit, which separates the water area of Taganrog Bay from the rest of the Sea of Azov, we consider the structure of the upper part of the geological section of these coastal accumulative forms. Core samples obtained during drilling made it possible to determine the change in thickness of Holocene sand-shell deposits and underlying Middle Pleistocene layers. It is shown that the formation of the spit began more than 5 ka ago during the initial stage of the New Black Sea transgression and occurred as a result of sequential attachment of beach bars to it.

Based on long-term data on the spatial distribution and fluxes of streaming (bubbling) methane in the Black Sea, the study considers various types of streaming gas emissions contributing to the methane content in the anoxic zone of the Black Sea. The estimate for the annual influx of methane gas emissions to the methane budget in the Black Sea was 1.2 × 109 m3 or 0.9 Tg, which is significantly less than the estimates obtained by biogeochemical methods (2.30–5.65 Tg yr–1).

The article presents the results of geophysical and geomorphological works on the western shelf of the Crimean Peninsula (Yevpatoriya–Balaklava). The sedimentary sequence structure, seafloor topography, and paleogeographic reconstructions of the formation conditions of the western shelf in the Late Pleistocene–Holocene are considered. Geoacoustic profile analysis aided in identifying the main shelf morphostructures; a brief description is presented. The abrasion–accumulative complex is identified, which consists of the abrasion platform and associated accumulative clinoform, the formation of which is related to the coastline of Late Pleistocene Black Sea regression to depths of about 90 m, traced from Yevpatoriya to Yalta. On the shelf of Kalamita Bay, fragments of a drowned river network and coastal accumulative landforms such as bars were studied.

—The article considers the long-term relief dynamics of the submerged slope of the Anapa bay-bar. The Anapa bay-bar consists of five morphological elements—Solenoe Lake, the Bugazskaya bay-bar, Blagoveshchensky butte, the Vityazevskaya bay-bar, and the Vityazevo–Anapa sector—and each has its own particular features of changes in the submerged slope. The erosion–accumulation sites alternate from year to year. In general, from 2012 to 2018, the amount of sediments on the submerged slope of the Anapa bay-bar decreased by 1.89 million m3. From 2012 to 2018, accumulation of 0.20 and 0.14 million m3 was observed in the area of Solenoe Lake and Blagoveshchensky butte, respectively. From 2012 to 2018, the submerged slope was eroded by 0.52 and 0.64 million m3 in the area of the Bugazskaya and Vityazevskaya bay-bars, respectively, and from 2013 to 2018, by 1.08 million m3, in the Vityazevo–Anapa sector. Approximately 600 m of coastal area is subjected to the greatest alteration along the profile to a depth of 6–7 m: submerged bars form and migrate in this area.

Data on the hydrocarbon composition of bottom sediments from a water area adjacent to an area with massive cottage construction (Kazach’ya Bay, coast of Sevastopol, the Black Sea) are presented. Analysis of bottom sediments performed in the summer 2015 provided values for the pH, Eh, natural humidity, and content of chloroform-extractable compounds, petroleum hydrocarbons, petrochemicals, polyaromatic hydrocarbons, and n-paraffins. Sites with unfavorable and moderately unsatisfactory ecological state were identified. The effect of urban development on the coast on the deterioration of bottom sediments was demonstrated.

Using a landscape approach, the paper presents for the first time the results of a comparative analysis of spatiotemporal changes in the macrophytobenthos, performed in the Laspi Bay for the period from 1983 to 2008 with landscape maps of Laspi Bay compiled by the authors. In addition, it describes the distribution of the bottom natural complexes with key Black Sea phytocoenoses. It was found that over a span of 25 years, the plant components of bottom natural complexes in Laspi Bay underwent significant restructuring and degradation due to natural factors and anthropogenic activity in the coastal zone.