The materials were obtained in the eastern part of the Kara Sea in September 2015 and 2022 and in the period of season ice formation in the last decade of October 2023 during 63, 89 and 92 cruises of RV “Arademik Mstislav Keldysh”. In the period of ice formation phytoplankton was characterized by poor species composition when dominating dinoflagellates and diatoms. Maximum numbers did not exсeed 3.5×10 cell/L, biomass was 5.0–25.2 mcg/L, which are the lowest values for the whole vegetation period in the Kara Sea. Higher species diversity, 2 to 3 times higher numbers and 5 to 10 times higher biomass of phytoplankton were observed in September. Latitudinal areas with different properties of pelagic environment, algae species complex and quantitative characteristics of phytoplankton were allocated. In all observations area of continental slope and external shelf border were characterized by maximum algae values of numbers and biomass. For inner shallow shelf high variability of environmental conditions and phytoplankton communities were typical. Existence of stable phytoplankton complex and similarity of seasonal suссession processes were established for extensive area of the middle shelf of the Kara Sea desalinated by riverine discharge with surface salinity from 25 to 30 PSU. In September – October “deep” maximum in phytoplankton vertical distribution characteristic for earlier periods of seasonal succession was absent.
Sukhanova et al. (2025) studied this question.