Valeriy K. Chasovnikov

Background. As a result of the functioning of the biological carbon pump (BCP), atmospheric carbon is converted into organic forms (organic pump) or inorganic forms such as calcite (carbonate pump). Relevance. The ocean accounts for nearly half of global carbon sequestration, making the study of these processes a relevant task in marine research. The aim of this work is to determine the hydrochemical conditions underlying the functioning of the organic and carbonate pumps in the Northeastern Black Sea in 2022 and to identify the factors responsible for the shift in their seasonal dynamics. Methods. In 2022, 14 expedition cruises (70 stations, 210 sampling depths) were carried out, with water sampling performed in the 0–50 m layer; temperature, salinity, and the concentrations of phosphorus, silicon, and inorganic nitrogen were measured, and quantitative and taxonomic analysis of phytoplankton was conducted. Results. An anomalous alteration of the timing of Emiliania huxleyi bloom (carbonate pump), which lasted from early June to late July, was recorded, while the period of diatom dominance (organic pump) shifted to August–September. Such a delayed and prolonged coccolithophore bloom, shifted by a full month, was documented for the first time. In 2022, the carbonate pump period was characterized by the following distinctive hydrological and hydrochemical features: stable water stratification with a shallow thermocline (located above the long-term average level) and high phosphorus concentrations combined with inorganic nitrogen deficiency. Conclusion. It was determined that the anomalous shift in the timing of carbonate pump functioning in 2022 resulted from a combination of factors: uncharacteristically stable stratification, persistent nitrogen deficiency, and elevated phosphorus concentrations in the active layer of the sea, which provided E. huxleyi with a competitive advantage for almost two months. Significant differences between the carbonate and organic pump dominance periods were revealed in temperature, salinity, silicon and nitrogen concentrations, and in the Si:N ratio. These findings improve our understanding of the switching mechanisms of the biological carbon pump in the Black Sea.

In the summer of 2022 and 2023, a shift was detected in the biological carbon pump system in the northeastern Black Sea, deviating from the traditional seasonal pattern: carbonate pump (late spring–early summer) → organic pump (summer–autumn). The coccolithophore Gephyrocapsa (=Emiliania) huxleyi (Lohmann) P. Reinhardt, 1972, responsible for the carbonate pump, dominated until the end of July, while the intensive growth of large diatom species representing the organic pump was shifted to August–September. These changes were associated with deviations in meteorological conditions from long-term averages. The absence of strong wind-induced mixing led to water column stabilization and the formation of a shallow thermocline. Low nitrogen and high phosphorus concentrations promoted a coccolithophore bloom in July, while low nitrogen levels prevented intensive diatom growth during summer. Thermocline deepening in September 2022 and August 2023 enhanced organic pump operation via a short-term bloom of the large diatom Pseudosolenia calcar-avis (Schultze) B.G. Sundström, 1986.

In this work, the dynamics of iron and manganese content in the surface layer of Gelendzhik and Blue Bays during 2023 was studied. Several exceedances of the MPC levels of iron and manganese were detected in both studied waters. High concentrations of iron and manganese are associated with strong winds and storm events, or with increased precipitation and large coastal runoff recorded on the eve of sampling.

The results of oceanological research carried out within the framework of the integrated scientific expedition "Black Sea-2023" and devoted to the study of the coastal zone of the sea on the basis of monitoring observations are presented. The hydrochemical parameters of the waters of the coastal shelf zone of the Black Sea are analyzed. In 2023, there was a decrease in the average annual stock of all biogenic elements in the active layer of the sea, compared with the hydrochemical background of 2022, and the minimum content of mineral nitrogen and phosphorus was recorded over the last six years of observations. Studies in areas with varying degrees of anthropogenic stress have revealed an improvement in the ecological state of the waters in the Gelendzhik Bay.

Экология гидросферы, Гидробиология

The biogeochemistry of waters is an essential regulator of phytoplankton dynamics, determining the level of species bloom and the change in dominants. This paper investigated the seasonal dynamics of phytoplankton and the nutrient concentrations and their ratios in the northeastern Black Sea in 2017–2021. Two taxonomic groups, diatoms and coccolithophores, determine the seasonal dynamics and significantly contribute to the total phytoplankton biomass. Coccolithophores formed blooms in early June annually, except in 2020. Large diatoms dominated in summer with a biomass exceeding 1000 mg m⁻³ annually, except in 2019. During the blooms of these taxonomic groups, their contribution to the total phytoplankton biomass exceeded 90%. Each group has characteristic biogeochemical niches in the nitrogen and phosphorus concentration coordinates. The position of the seasonal thermocline regulates the biogeochemistry of the water. With a high-lying and sharp gradient thermocline (the average for five years is 6.87 m), low nitrogen concentrations and a nitrogen-to-phosphorus ratio below the Redfield ratio are created in the upper mixed layer. These conditions are optimal for the dominance of coccolithophores. When the thermocline is deepened (the average for five years is 17.96 m), the phosphorus concentration decreases significantly and the ratio of nitrogen to phosphorus is significantly higher than the Redfield ratio, and these conditions lead to the dominance of large diatoms. The results of experimental studies with nitrogen and phosphorus additives in the natural phytoplankton population confirm the above statements. The addition of phosphorus leads to the increased role of coccolithophores in the total phytoplankton biomass, the addition of nitrogen alone contributes to the growth of large diatoms, and the combined addition of phosphorus and nitrogen in a ratio close to the Redfield ratio leads to the dominance of small diatoms.

Biogeochemistry of waters is an essential regulator of phytoplankton dynamics, determining the level of species bloom and the change of dominants. The paper investigated the seasonal dynamics of phytoplankton and the nutrient concentration and their ratios in the NE Black Sea in 2017-2021. Two taxonomic groups, diatoms, and coccolithophores, determine seasonal dynamics and significantly contribute to the total phytoplankton biomass. Coccolithophores annually, except in 2020, formed bloom in early June. Large diatoms in summer annually, except in 2019, dominated with biomass exceeding 1000 mg m-3. During the bloom of these taxonomic groups, their contribution to the total phytoplankton biomass exceeded 90%. Each group has characteristic biogeochemical niches in the nitrogen and phosphorus concentrations coordinates. The regulation of the biogeochemistry of water is the position of the seasonal thermocline. With a high-lying and sharp gradient thermocline (the average for five years is 6.87 m), low nitrogen concentrations and a nitrogen-to-phosphorus ratio below the Redfield ratio are created in the upper mixed layer. These conditions are optimal for the dominance of coccolithophores. When the thermocline is deepened (the average for five years is 17.96 m), the phosphorus concentration decreases significantly and the ratio of nitrogen to phosphorus is significantly higher than the Redfield ratio, and these conditions lead to the dominance of large diatoms. The results of experimental studies with nitrogen and phosphorus additives in the natural phytoplankton population confirm the above statements. The addition of phosphorus leads to an increased role of coccolithophores in the total phytoplankton biomass, the addition of nitrogen alone contributes to the growth of large diatoms, and the combined addition of phosphorus and nitrogen in a ratio close to the Redfield ratio leads to the dominance of small diatoms.

The results of long-term oceanological studies that were carried out as part of the Black Sea 2017–2021 complex scientific expedition and are devoted to the study of the coastal zone of the sea based on monitoring observations are presented. During all five years, a stable trend of a decrease in the content of silicon in the active layer of the coastal-shelf zone of the sea was observed. During the last 3 years, there has been an increase in the reserves of mineral phosphorus and a decrease in the content of mineral nitrogen. As a result of this variability in the content of phosphorus, nitrogen and silicon, during 2021, such stoichiometric relationships between them were established that a rare situation arose in the hydrochemical regime of the Black Sea waters. Phosphorus ceases to be the main element limiting the processes of development of biological communities, and among the three main biogenic elements, any of the parameters could act as a limiting factor or have a joint limiting effect on the development of photosynthesis.

Aim.To study the state of the marine ecosystem of the recreational‐tourist zone of the Caucasian sector of the Black Sea through the example of a beach near the mouth of the Agoy River.Material and Methods. Phytoplankton, heterotrophic bacterioplankton, infusoria, holoplankton, meroplankton, ichthyoplankton, zoobenthos of loose bottom sediments and hydrochemistry samples of the water and bottom sediments were collected in June 2012 on three sections from the mouth of the Agoy River to the coastal runoff zone (depths 2.5–7.5 m). The identification of species of plankton and of the zoobenthos and of the chemical parameters of water and sediments was carried out according to standard methods. Results.It was revealed that most of the beach area, where psammophilic biocenoses of Lucinella divaricate and Chamelea gallina (Bivalvia) were located, was in satisfactory condition. An increase in the density of Lucinella divaricate, a rare species in the late 1990s, was noted. In the runoff zone, there was observed the appearance of cyanobacteria and the suppression of zoobenthos, expressed through the replacement of mollusc biocenoses by the biocenosis of the polychaete, Capitella capitate, with a biomass two orders of magnitude lower than the average for the area. High numbers of heterotrophic bacterioplankton (4.5 million cell/ml) and infusoria (64 million ind./m3) could indicate bacterial contamination of this zone. The negative impact of waste water on plankton is manifested in a decrease in the population of netted zooplankton, their abnormal development, and the increasing role of microheterotrophs.Conclusions.The results obtained give an image of the state of marine coastal ecosystems of recreational‐tourist and cordoned areas of the Caucasus and can be useful for the further monitoring of this region.

In the course of studies of hydrochemical monitoring data for the period from 2017 to 2019, we found that the Gelendzhik bay, which belongs to semi-closed water areas, has an increased background of mineral and organic nitrogen forms compared to the background in the Golubaya bay corresponding to the open coast. Increased concentrations of mineral forms of nitrogen in the Gelendzhik bay we detected, probably due to anthropogenic impact.