The Arctic climate strongly affects phytoplankton production and biomass through several mechanisms, including warming, sea ice retreat, and global atmospheric processes. In order to detect the climatic changes in phytoplankton biomass, long-term variability of chlorophyll a (Chl-a) was estimated in situ with the changes in the surface sea temperature (SST) and salinity (SSS) in the Barents Sea and adjacent waters during the period of 1984–2021. Spatial differences were detected in SST, SSS, and Chl-a. Chl-a increased parallel to SST in the summer-autumn and spring periods, respectively. Chl-a peaks were found near the ice edge and frontal zones in the spring season, while the highest measures were observed in the coastal regions during the summer seasons. SST and Chl-a demonstrated increasing trends with greater values during 2010–2020. Generalized additive models (GAMs) revealed that SST and Chl-a were positively related with year. Climatic and oceanographic variables explained significant proportions of the Chl-a fluctuations, with six predictors (SST, annual North Atlantic Oscillation index, temperature/salinity anomalies at the Kola Section, and sea ice extent in April and September) being the most important. GAMs showed close associations between increasing Chl-a and a decline in sea ice extent and rising water temperature. Our data may be useful for monitoring the Arctic regions during the era of global changes and provide a basis for future research on factors driving phytoplankton assemblages and primary productivity in the Barents Sea.

Effects of the sea-ice edge and the Polar Frontal Zone on the distribution of chlorophyll-a levels in the pelagic were investigated during multi-year observations in insufficiently studied and rarely navigable regions of the Barents Sea. Samples were collected at 52 sampling stations combined into 11 oceanographic transects over a Barents Sea water area north of the latitude 75° N during spring 2016, 2018, and 2019. The species composition, abundance and biomass of the phytoplankton community, chlorophyll-a concentrations, hydrological and hydrochemical parameters were analyzed. The annual phytoplankton evolution phase, defined as an early-spring one, was determined throughout the transects. The species composition of the phytoplankton community and low chlorophyll-a levels suggested no phytoplankton blooming in April 2016 and 2019. Not yet started sea-ice melting prevented sympagic (sea-ice-associated) algae from being released into the seawater. In May 2018, ice melting began in the eastern Barents Sea and elevated chlorophyll-a levels were recorded near the ice edge. Chlorophyll-a concentrations substantially differed in waters of different genesis, especially in areas influenced by the Polar Front. The Polar Front separated the more productive Arctic waters with a chlorophyll-a concentration of 1–5 mg/m³ on average from the Atlantic waters where the chlorophyll-a content was an order of magnitude lower.

We studied the spatial patterns of the planktonic ecosystems at two Arctic sites strongly affected by Atlantic Inflow (FS, the Fram Strait; and BS, the Barents Sea). A high degree of similarity in the bacterial abundance (mean: 3.1 × 10⁵ cells mL⁻¹ in FS vs. 3.5 × 10⁵ cells mL⁻¹ in BS) was found, while other plankton characteristics were different. Bacterial biomass reached a maximum in BS (3.2–7.9 mg C m⁻³), while viral abundances tended to be higher in FS (2.0–5.7 × 10⁶ particles mL⁻¹). Larger bacterial cells were found in BS, suggesting the presence of different bacterial populations at both locations. The virus-to-bacteria ratio was significantly higher in FS than in BS (13.5 vs. 4.7). Chlorophyll a concentration was extremely low (<0.25 mg m⁻³). The highest zooplankton abundance was in the surface layer (919 individuals m⁻³ in FS vs. 602 ind. m⁻³ in BS). Zooplankton biomass strongly varied (1–39 mg C m⁻³), with the maximum in BS. High proportions of boreal taxa in the total zooplankton abundance indicate the Atlantification of pelagic ecosystems in the Arctic. Plankton indicators are correlated with temperature, salinity, and sampling depth. Strong intercorrelations were found between major plankton groups, suggesting tight links in the studied plankton ecosystems.

This paper describes the comprehensive studies of phytoplankton carried out in April 2018 in the northwestern Barents Sea, in the Polar Front region (74.8°–76.2° N), at a distance of 10–100 km from the ice edge at depths ranging from 0 to 50 m. The hydrological, hydrochemical, and microbiological parameters of the seawater are determined simultaneously. An early-spring species complex is observed on both sides of the front; 90% of the biomass of which is formed by the diatoms Pauliella taeniata, Fragilariopsis oceanica, and Thalassiosira antarctica var. borealis. The taxonomic composition of microalgae communities in water masses of different origin has an 83% similarity. The average abundance and biomass of microalgae and chlorophyll-a content per m² in Atlantic waters reaches 37 170 cells/L, 0.12 μg/L, and 0.5 mg/m³, respectively. In Arctic waters, these values are about 30 times higher, 0.87 million cells/L, 2.59 μg/L, and 3.13 mg/m³, respectively. The results obtained suggest that the Polar Front is not a boundary between various algal communities, but separates highly productive Arctic waters from Atlantic waters with low phytoplankton abundance.

In the marine environment, bacteria and viruses play a significant role in carbon fluxes, remineralization processes, and the infection of various organisms. We performed a survey in the northeastern Barents Sea, a region adjacent to the Arctic Ocean, to investigate spatial patterns of microbial plankton, after the main productive period, in October 2020. Two main water masses occurred in the study region—colder Arctic Water and warmer Barents Sea Water, representing transformed Atlantic Water. Multivariate analyses detected patchiness in the horizontal distribution of bacteria and viruses, and their abundances showed no clear association with the water masses. There was an obvious vertical pattern in microbial concentration, with the highest estimates in the upper layers. Surface viral and bacterial abundance varied in a wide range (2.20 × 10⁵–10.7 × 10⁵ cells·mL⁻¹ and 0.86 × 10⁶–14.98 × 10⁶ particles·mL⁻¹, respectively) and were correlated with each other. Bacterioplankton was dominated by small-sized cells (<2 μm, 0.04–0.06 µm³), and the average volume of bacterial cells tended to increase toward the seafloor. The ratio of viral to bacterial abundance (VBR) was 11 ± 1 and did not differ between water masses and depth layers. VBR were higher, compared to summer values, suggesting a strong impact of viruses on bacterioplankton, after the main productive season. Redundancy and correlation analyses showed that inorganic nutrients (nitrate and phosphate) and organic carbon from zooplankton were most responsible for the total variability in the microbial parameters. Water temperature and salinity, also, had a measurable impact, but their influence was lower. Bacterial abundance was lower than in other seasons and regions of the Barents Sea, while viral abundance was comparable, suggesting a stronger viral impact on Arctic marine bacteria in the autumn season.

In spring 2016, the thermohaline characteristics of water masses and the distribution of chlorophyll-a concentration in the pelagic zone of the eastern part of the Barents Sea were studied. For the first time, in the conditions of an abnormally warm year and the absence of ice cover, a complex of hydrobiological works was carried out on a section crossing the Barents Sea from south to north along the western coast of the Novaya Zemlya archipelago. High concentrations of chlorophyll-a > 1 ˂ 6 mg/m³ at all stations of the transect indicate a stage of spring bloom in the successional cycle of microalgae. Significant differences in the content of chlorophyll-a in waters of various origins were revealed. The highest concentrations of chlorophyll-a corresponded to Arctic surface water (5.56 mg/m³). Slightly lower values were observed in the transformed Atlantic waters of the Novozemelskoe and Kolguevo–Pechorskoe currents (3.53 ± 0.97–3.71 ± 1.04 mg/m³), and the lowest was in the Barents waters (1.24 ± 0.84–1.45 ± 1.13 mg/m³).