Vladimir A. Silkin

In the Fram Strait, Atlantic Water (AW) flows northward through the eastern part of the strait, while Polar Surface Water (PSW) moves southward from the Arctic Ocean through its western part. Mixing of these water masses produces mixed AW (mAW). As these water masses move, significant changes occur in salinity, temperature, density, and nutrient concentrations, restructuring the phytoplankton community. Based on surveys conducted in August 2021 during the 84th cruise of the R/V Akademik Mstislav Keldysh, the dominant species were identified for each water mass. Among the key species (10 diatoms, 11 dinoflagellates, two coccolithophores, and one species each of chrysophyte, haptophyte, and ciliates), three ecological assemblages were distinguished: a cold-water PSW indicator complex (Porosira glacialis and Rhizosolenia hebetata f. hebetata among diatoms, the dinoflagellate Protoperidinium islandicum, and the ciliate Mesodinium rubrum); a warm-water AW complex (Navicula planamembranacea, Stephanopyxis turris, Rhizosolenia styliformis, the dinoflagellates Protoperidinium depressum and Tripos spp., and the coccolithophore Coccolithus pelagicus); and an mAW complex (the diatom Thalassiosira rotula, the coccolithophore Gephyrocapsa huxleyi, the haptophyte Phaeocystis pouchetii, and the chrysophyte Monochrysis sp.). Moving from south to north into the Fram Strait and from east to west towards the Greenland shelf, warm-water Atlantic indicator species were first replaced by mAW species, and then by cold-water species in the PSW. Maximum phytoplankton biomasses (up to 670.8 mg/m³) were observed in the marginal ice zone, driven by the intensive growth of large diatoms at depths within the euphotic zone where AW and PSW interact. If this interaction depth lies outside the euphotic zone, the phytoplankton biomass is determined by ciliates. In open water, large dinoflagellates contributed most to the biomass, indicating the decisive role of mixoplankton (mixotrophic plankton) in summer at high Arctic latitudes.

This article assesses the effectiveness of digital platforms as social media tools in electoral campaigns and the impact of digital platform algorithms on audience political behavior. Using secondary analysis of statistical data from research companies DataReportal, We Are Social, and Mediascope for 2014-2024, a comparative study was conducted of six social networks (Facebook, YouTube, Instagram, Twitter/X, TikTok, and VK) in six countries (the United States, Germany, Brazil, India, France, and Russia). It was found that Twitter/X (up to 0.58) and Facebook (up to 0.51) demonstrate the highest correlation between political discussions and voter turnout, while YouTube and Instagram, despite their high reach, show low conversion rates due to the predominance of entertainment content. A national specificity was identified: in Russia, the key platforms are VK (correlation 0.37) and YouTube (0.35) due to the current geopolitical situation.

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.

During the 84th cruise of the R/V Akademik Mstislav Keldysh in August 2021, patterns of phytoplankton composition transformation were revealed along a northward gradient. The study involved three transects in the Fram Strait and adjacent Arctic waters: a southern transect (from the Barents Sea shelf to the Greenland shelf), a middle transect across the Fram Strait, and a northern transect along the ice edge. Ten species of diatoms and eleven of dinoflagellates were identified, and their ecological preferences were characterized by determining the minimum, maximum, mean, and median values for abundance, biomass, depth of the biomass maximum, salinity, temperature, and the concentrations and ratios of nitrogen, phosphorus, and silicon. Significant gradients in temperature, salinity, silicon, and nitrogen concentrations were recorded along the south–north direction in the study area. The phytoplankton community responds to these changing factors through restructuring. Dinoflagellates predominantly dominate the southern and middle transects, whereas large diatoms make a substantial contribution to the phytoplankton biomass in the northern transect. Diatom biomass is determined by nitrogen concentration. The dependence of dinoflagellate biomass on that of small flagellates confirms the importance of mixotrophic nutrition. A hypothesis is proposed that the most probable criterion for the selective selection of diatoms northward is the half-saturation constant for nitrogen uptake, while for dinoflagellates, it is temperature.

During the 84th cruise of the R/V Akademik Mstislav Keldysh in August 2021, patterns of phytoplankton composition transformation were revealed along a northward gradient. The study involved three transects in the Fram Strait and adjacent Arctic waters: a southern transect (from the Barents Sea shelf to the Greenland shelf), a central transect across the Fram Strait, and a northern transect along the ice edge. Ten species of diatoms and eleven of dinoflagellates were identified, and their ecological preferences were characterized by determining the minimum, maximum, mean, and median values for abundance, biomass, depth of the biomass maximum, salinity, temperature, and the concentrations and ratios of nitrogen, phosphorus, and silicon. All identified species are of Atlantic origin. In summer, within the relatively warm Atlantic Waters, phytoplankton biomass was dominated by dinoflagellates of the genus Tripos and Protoperidinium depressum. Diatoms contributed insignificantly, with Stephanopyxis turris, Navicula planamembranacea, and Thalassiosira gravida being the most frequently observed. Northward, towards the Fram Strait, the dinoflagellate community shifted to include Protoperidinium breve, Protoperidinium brevipes, and Prorocentrum cordatum, while diatoms were increasingly represented by Thalassiosira rotula, Chaetoceros borealis, and Rhizosolenia styliformis. A further decline in temperature and salinity favored the dominance of the dinoflagellates Protoperidinium pellucidum and Gyrodinium lachryma, and the diatoms Eucampia groenlandica, Rhizosolenia hebetata f. semispina, and Rhizosolenia hebetata f. hebetata. The dinoflagellates Protoperidinium granii and Protoperidinium islandicum, along with the diatom Porosira glacialis, thrived at the lowest temperatures and salinities. Diatoms generally grew at silicon concentrations of 1–3 µM and nitrogen concentrations above 1 µM, except for R. hebetata f. semispina, R. hebetata f. hebetata, and Porosira glacialis. The dinoflagellates P. depressum, P. islandicum, P. brevipes, P. breve, and Gyrodinium lachryma were associated with lower nitrogen concentrations (< 2 µM), while others preferred higher levels. Diatom biomass was regulated by ambient nitrogen concentration, whereas dinoflagellate biomass was correlated with the biomass of small flagellates.

The modern Arctic is characterized by a decreased ice cover and significant interannual variability. However, the reaction of the High Arctic ecosystem to such changes is still being determined. This study tested the hypothesis that the key drivers of changes in phytoplankton are the position and intensity of Atlantic water (AW) flow. The research was conducted in August 2017 in the northern part of the Barents Sea and in August 2020 in the Nansen Basin. In 2017, the Nansen Basin was ice covered; in 2020, the Nansen Basin had open water up to 83° N. A comparative analysis of phytoplankton composition, dominant species, abundance, and biomass at the boundary of the ice and open water in the marginal ice zone (MIZ) as well as in the open water was carried out. The total biomass of the phytoplankton in the photic layer of MIZ is one and a half orders of magnitude greater than in open water. In 2017, the maximum abundance and biomass of phytoplankton in the MIZ were formed by cold-water diatoms Thalassiosira spp. (T. gravida, T. rotula, T. hyalina, T. nordenskioeldii), associated with first-year ice. They were confined to the northern shelf of the Barents Sea. The large diatom Porosira glacialis grew intensively in the MIZ of the Nansen Basin under the influence of Atlantic waters. A seasonal thermocline, above which the concentrations of silicon and nitrogen were close to zero, and deep maxima of phytoplankton abundance and biomass were recorded in the open water. Atlantic species—haptophyte Phaeocystis pouchettii and large diatom Eucampia groenlandica—formed these maxima. P. pouchettii were observed in the Nansen Basin in the Atlantic water (AW) flow (2020); E. groenlandica demonstrated a high biomass (4848 mg m⁻³, 179.5 mg C m⁻³) in the Franz Victoria trench (2017). Such high biomass of this species in the northern Barents Sea shelf has not been observed before. The variability of the phytoplankton composition and biomass in the Franz Victoria trench and in the Nansen Basin is related to the intensity of the AW, which comes from the Frame Strait as the Atlantic Water Boundary Current.

The seasonal dynamics of the NE Black Sea phytoplankton follow the following pattern: small diatoms (spring) → coccolithophorid Emiliania huxleyi (late spring–early summer) → large diatoms (summer). Our hypothesis states that nitrogen and phosphorus concentrations regulate the seasonal phytoplankton dynamics. A minimum number of parameters is enough to understand the mechanisms of dominant species change. Based on the concept of intracellular regulation, the following parameters were evaluated: the minimum nitrogen and phosphorus quotas; half-saturation constants for nitrogen and phosphorus uptake; the maximum specific growth rate of the dominant phytoplankton species. Computational experiments on the model show the following: (1) in spring, a species with a high maximum specific growth rate becomes dominant; (2) in late spring and early summer, a species with a low minimum nitrogen quota and a low half-saturation constant for nitrogen uptake is observed; (3) in summer, a low minimum phosphorus quota and a low half-saturation constant for phosphorus uptake allow the species to become dominant.

Экология гидросферы, Гидробиология

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.