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.

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).

The paper considers the dependence of changes in the area of ice in the Kara Sea with fluctuations of the Ob and Yenisei rivers runoff during the period from 1978 to 2022. Over the period from 2004 to 2022, statistically significant positive correlations between the summary runoff of the Ob and Yenisei and the area of ice in the Kara Sea were found. There was an acceleration of ice formation processes, an elongation of the ice stabilization period, the beginning of ice melting in a later date and a higher resistance of ice to destruction during summer in the high-water content years of the Ob and Yenisei rivers.

In April 2018, complex studies of phytoplankton communities were carried out in the northwestern Barents Sea in the region of the Polar Front (74.8°-76.2° N) in a layer of 0-50 m. The region under study encompassed surface Arctic water and Atlantic water of the Fram branch (which conditionally corresponds to the Arctic water mass) divided from the Atlantic water mass by the Polar Front. Phytoplankton community on both sides of the front were represented by early spring complex, 90% of biomass was formed by diatoms (Achnanthes taeniata, Nitzschia grunowii, Thalassiosira antarctica). In water of Atlantic origin Phaeocystis pouchetii were found among the dominants. However, the level of development of microplankton was significantly higher in water from the Arctic Basin. The highest chlorophyll-a concentrations referred to surface Arctic water (3.13±0.43 mg/m³) and Atlantic Fram water (2.04±0.29 mg/m³). The concentration of chlorophyll-a at the stations performed in the Atlantic water mass was an order of magnitude lower - 0.50±0.26 mg/m³. Thus, during the early-spring period, the Polar Front is a powerful boundary that limits exclusively the level of development and quantitative indicators of the early spring microphytoplankton complex. The front line separates the more productive Arctic water, with average chlorophyll-a concentrations of 2-3 mg/m³, from the Atlantic water, in which concentrations of this pigment are an order of magnitude lower.

The ice cover variability of the Kara and Laptev seas in 1978–2022 and the effect of river runoff fluctuations on the ice processes in the seas are s