№ 1 (2024)

The Stokes drift generated by surface waves affects many physical processes occurring in the coastal zone of the sea, including heat and salt transport, as well as transport of pollutants. Taking into account the parameters of sea currents caused by the Stokes drift is important for a more correct description of the general hydrodynamic structure of coastal waters. Moreover, sea currents generated by surface waves make a significant contribution to the processes of accumulation and redistribution of pollutants in the coastal zone of the sea. The article presents the results of the study of the Stokes drift on the northeastern shelf of the Black Sea near Gelendzhik for the period from 2003 to 2022. Seasonal and interannual features of variability of Stokes current velocities and directions have been identified. It has been shown that from December to April, excluding February, the Stokes transport has comparable repeatability in directions towards the coast, away from the coast, and towards the northwest. In February, the main flow tends to the open sea. In May and June, the repeatability of currents towards the coastline increases significantly, with the contribution of currents to the southeast increasing at the beginning of summer. In July, the currents directed to the southeast and away from the coast become almost identical in terms of repeatability. From August to November, the proportion of currents directed away from the coast increases with a gradual decrease in the repeatability of currents towards the southeast. In multi-year terms, the flow directed away from the coast to the open sea prevails (repeatability of 34.3%). The same flow has the highest mean velocity (0.053 m/s). Repeatability of the long-shore currents directed towards the southeast and northwest is almost the same, but the currents towards the northwest are much more intense.

The paper analyses decade-average (2013–2022) statistical and spectral characteristics of mesoscale and synoptic variability of the wind field for the atmosphere surface layer and the surface current to reveal regularities and peculiarities of the wind variability and quasi-stationary alongshore current near Cape Kikineiz of the Southern Coast of Crimea. Complex instrumental monitoring was carried out under open sea conditions using clusters of hydrometeorological and oceanological meters at the stationary oceanographic platform of the Black Sea hydrophysical sub-satellite testing area of Marine Hydrophysical Institute of RAS. The author used a dataset of chronological sequences of mean-hourly vector-averaged data for May–October and November–April half-year periods to quantify the values and identify trends in the interseasonal variability of wind and current field characteristics. During the selected time periods, clear seasonal differences in the thermal structure and dynamics of both the surface wind field and coastal waters were observed near the coast. Based on instrumental monitoring materials, peculiarities of coastal water circulation under seasonal variability of local wind conditions were studied. The spectral analysis results estimate the energy contribution of breeze wind circulation to the seasonal intensification of the mesoscale variability of the alongshore current. During the entire annual cycle, multiscale alongshore reciprocating wind fluctuations, parallel to the Main Ridge of the Crimean Mountains, were detected at the seacoast apart from the background large-scale wind field. Such wind fluctuations influence the variability of the coastal-waters alongshore circulation, which allows studying the conditions and peculiarities of the bimodal distribution formation of the direction recurrence of the quasi-stationary alongshore current near Cape Kikineiz.

Carbon dioxide is one of the green gases and its entry into the atmosphere and further redistribution in the waters of the World Ocean not only plays a significant role in the climate on the Earth, but also affects the characteristics of waters. The research of inland seas, e.g. the Black Sea, makes it possible to study the influence of atmospheric CO₂ on the characteristics of waters and to assess the contribution of regional ecosystems to the total budget of the CO₂ flux of the World Ocean. The paper presents numerical estimates of the sea–air CO₂ flux, analyzes its direction and identifies factors that determine the values of the CO₂ flux in the northeastern part of the Black Sea during a cold period. For the analysis, the data obtained during the cruise of R/V Professor Vodyanitsky in December 2022 were used. The values of the sea–air flux of carbon dioxide were calculated taking into account the wind speed and pCO₂ gradient between the sea surface and the near sea surface atmosphere.
According to the direct measurements of pCO₂, the value of the CO₂ flux in December 2022 varied widely from ‒0.05 to ‒8.74 mmol·m^‒2·day^‒1, the average value being ‒2.11 ± 1.79 mmol·m^‒2·day^‒1. It was established that during the cold season, the CO₂ flux was directed from the atmosphere to the sea surface. Thus, the waters of the Crimean coast serve as a stock of atmospheric CO₂. Local minima of flux values were observed in the southeastern regions of the Crimean coast. When analyzing the correlation of the CO₂ flux with temperature, wind speed and ΔpCO₂, the strongest relationship was found with wind speed (‒0.93), while the weakest one was with ΔpCO₂ (0.22). Therefore, the intensity of the sea–air CO₂ flux was determined by wind speed, while the direction of the flux was determined by ΔpCO₂. The temperature contribution manifested as change in the concentration of CO₂ in the water column.

Nutrient concentration in the water of sea mouths of rivers is a limiting factor in the life activity of hydrobionts. Therefore, studying this parameter is important for assessing the current state of mouth ecosystems and its forecasting. Until now, the variability of nutrients has been analysed by their average concentrations over heterogeneous or short-term periods, extremes or individual surveys, which do not reflect the regime of these elements in the modern climatic period. The paper aims to give a modern description of the nutrient concentration variability in the Chernaya River estuarine zone and to assess water quality based on these components of the ecosystem. For the analysis, we used data from hydrochemical surveys for 1991–2020. Water quality was assessed by the nutrient water pollution index, whereas self-purifying capacity of the estuarine zone was assessed using a transformation index of selected nutrients. The distributions of nutrient concentrations were found to be extremely asymmetrical. In this regard, we obtained for the first time the distributions of medians of nitrates, nitrites, ammonium nitrogen and phosphates in the water of the Chernaya River estuarine zone. In the study area, these median concentrations of nutrients did not exceed the maximum permissible values. Analysis of the temporal variability of average annual nutrient concentrations showed the absence of significant trends. The obtained results can be used for balance estimates and calculations of the assimilation capacity of the Chernaya River estuarine zone.

The paper assesses the quality of the marine environment of Laspi Bay near the Batiliman Stow according to main chemical and microbiological parameters under various recreational impacts on the water area. The material for the study was water and fouling samples taken in May, July and October 2023. The qualitative and quantitative composition of hydrocarbons was determined by gas chromatography on a Crystal 5000.2 chromatograph with a flame ionization detector in the Scientific and Educational Center for Collective Use «Spectrometry and Chromatography» of A. O. Kovalevsky Institute of Biology of the Southern Seas of RAS. Diagnostic markers of the origin of hydrocarbons were used to identify possible sources of organic substances. The abundance of bacteria groups (saprophytic heterotrophic, hydrocarbon-oxidizing, lipolytic and phenol-oxidizing) was determined by the method of tenfold dilutions using elective nutrient media. From May to October 2023, the concentration of hydrocarbons in the coastal waters of the Batiliman Stow was 0.013–0.304 mg∙L^–1. The composition of n-alkanes indicated the absence of oil pollution in the studied water area. The exceedance of the maximum permissible concentration for hydrocarbons, noted in July at one of the stations, is of natural origin and is associated with an active intake of allochthonous compounds. The quantitative assessment of the mentioned bacteria groups in the water and microperiphyton of macrofouling indicates an increase in the abundance of indicator groups of bacteria in all samples taken in July. Nevertheless, the results of the hydrocarbon content study and the quantitative assessment of the main microbiological indicators in the water and microperiphyton of macrofouling suggest that there are active bacterial self-purification processes in the water area of the Batiliman Stow. According to microbiological indicators, the studied area can be classified as conditionally clean.