Primary production (PP) and chlorophyll “a” concentration (chl “a”) estimates in the Eurasian Arctic are discussed, where the continued climatic warming with increased “Atlantification” advance the sea ice losses. The maximum integrated PP and the total chl “a” content observed in the marginal ice zone (MIZ) of the Barents Sea with weakened stratification of the water column and reached 1109 mgC m–2 day–1 and 118 mg m–2. Nearby the ice edge in the Nansen Basin, the main part of PP formed in the upper mixed layer and did not exceed 469 mgC m–2 day–1, the chl “a” content of 56 mg m–2. In the early and late phytoplankton bloom in MIZ, the typical leading role of picophytoplankton in carbon fixation revealed. Large centric diatoms, microphytoplankton, dominated at the peak bloom stage in 2020 with the dense marine ice cover of the Nansen Basin. A similar phenomenon was previously observed only in the Arctic shelf seas and was not recorded in the high-latitude basins of the Arctic Ocean. With the sparse ice cover of the Nansen Basin in 2021, the main primary producers at the peak bloom were pico- and nanophytoplankton. The low variability of assimilation numbers at all bloom stages (1.7 ± 0.3 mgC mg chl “a”–1 h–1) indicates the acclimatization of phytoplankton to changing environment. The ecological flexibility of the primary production are link of the MLZ ecosystems in the studied seas of the European Arctic during the period of climate change is confirmed.