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Size-fractionated surface phytoplankton in the Kara and Laptev seas: environmental control and spatial variability

Andrey B. Demidov*, Irina N. Sukhanova, Tatiana A. Belevich, Mikhail V. Flint, Vladimir I. Gagarin, Valentina M. Sergeeva, Elena V. Eremeeva, Alexey V. Fedorov

*Corresponding author:

ABSTRACT: Climate-induced variability of phytoplankton size structure influences primary productivity, marine food web dynamics, biosedimentation, and exchange of CO2 between the atmosphere and ocean. Investigation of the phytoplankton size structure in the Arctic Ocean is important due to rapid changes in its ecosystems related to increasing temperature and declining sea ice cover. This study aims to estimate the contribution of surface micro-, nano- and picophytoplankton to the total carbon biomass (B), chlorophyll a concentration (chl a) and primary production (PP) in the Kara and Laptev seas and to study the relationships of these phytoplankton size groups with environmental factors which determine their spatial variability. Additionally, the comparison between chlorophyll specific carbon fixation rate (Pb), specific growth rate (µ), and carbon to chlorophyll ratio (θ) of phytoplankton size groups was performed. The investigation was carried out from August to September 2018. Generally, picophytoplankton was dominant in terms of Chl a and PP in the whole studied area. It was shown that the spatial variability of phytoplankton size classes was influenced by the river discharge and relies mainly on water temperature, salinity and dissolved silicon concentration. Microphytoplankton prevailed over the River runoff region under conditions of low salinity and relatively high water temperature, while picophytoplankton was predominant under conditions of high salinity and low water temperature. Being the first to characterize size-fractionated phytoplankton abundance in the Kara and Laptev seas, our study provides a baseline for future assessment of the response of Kara and Laptev seas ecosystems to climate-induced processes using the phytoplankton size structure.