Role of Plankton in the Vertical Flux of Particulate Organic Carbon in the Kara Sea during the Autumn–Winter Transition Period

Abstract— The study is based on material collected by sequential sediment traps moored on the outer shelf of the Kara Sea slope during the 2020 autumn–winter transition period. Small sediment traps were used to estimate the annual flux. The flux of total sedimentary matter and of particulate organic carbon (POC) increased from 0.8 g m^–2 d^–1 and 0.02 gC m^–2 d^–1 in September to 4.5 g m^–2 d^–1 and 0.08 gC m^–2 d^–1 in December. The contribution of the POC flux to the total matter flux decreased from 2.6% to 1.9%. The flux of the planktonic components was determined by zooplankton fecal pellets, whose contribution to the biogenic POC flux decreased from 20% in September to 1% in December. The contribution of protists to the biogenic POC flux decreased from 2.2% in September to 0.1% in December. The influence of the river runoff was manifested in the multiple increase in fluxes of fecal pellets and protists compared to the values measured in the autumn on the outer shelf of the Kara Sea not affected by the river plumes. Annual fluxes of sedimentary matter and POC measured by small sediment trap data increased with depth from 341.4 g m^–2 year^–1 and 7.0 gC m^–2 year^–1 at 70 m to 864.1 g m^–2 year^–1 and 12.4 gC m^–2 year^–1 at 150 m. The total contribution of all planktonic components to the annual biogenic POC flux was 48% at 70 m and 20% at 150 m.