Spatial Distribution of Picophytoplankton in the White Sea in the Beginning of Summer

Abstract

Biomass of photosynthetic picoplankton (B_pic), its contribution to the total phytoplankton biomass (B_pic%), chlorophyll a concentration (Chl), and associated hydrophysical characteristics of the water masses in the White Sea were estimated in June 2015 at 47 stations located in the open parts and in the inlets of the Onega and Kandalaksha Bays and in the western part of the Basin. Spatial variability of mean values of B_pic in the photic layer (0.01–1.91 mg C/m³) was preconditioned by sub- and mesoscale heterogeneity of the hydrological conditions. The values of B_pic were higher near the frontal zones than those in the water masses characterized by quasi-homogeneous distribution of the thermohaline characteristics. The relative contribution of B_pic did not exceed 1% at half of the stations and varied from 1 to 8% for the rest of the studied water area. The value of B_pic% reached 40.5% in the Basin and did not exceed 2% during the phytoplankton bloom in Knyazhaya Inlet (Chl > 3 mg/m³) accompanied by the dominance of Skeletonema costatum sensu lato.