The northern Barents Sea is a productive Arctic inflow shelf with a seasonal ice cover and as such, a location withan efficient downward export of particulate organic matter through the biological carbon pump. The region isunder strong influence of Atlantification and sea-ice decline, resulting in a longer open water and summer period.In order to understand how these processes influence the biological carbon pump, it is important to identify theseasonal and spatial dynamics of downward vertical flux of particulate organic matter. In 2019 and 2021, shortterm sediment traps were deployed between 30 and 200 m depth along a latitudinal transect in the northwesternBarents Sea during March, May, August and December. Vertical flux of particulate organic carbon, δ¹³C and δ¹⁵Nvalues, Chl-a, protists and fecal pellets were assessed. We identified a clear seasonal pattern, with highest verticalflux in May and August (178 ± 202 and 159 ± 79 mg C m^{− 2} d^{− 1}, respectively). Fluxes in December and Marchwere < 45 mg C m^{− 2} d^{− 1}. May was characterized by diatom- and Chl a-rich fluxes and high spatial variability,while fluxes in August had a higher contribution of fecal pellets and small flagellates, and were spatially morehomogenous. Standing stocks of suspended particulate organic matter were highest in August, suggesting a moreefficient retention system in late summer. The strong latitudinal sea-ice gradient and the influence of AtlanticWater probably led to the high spatial variability of vertical flux in spring, due to their influence on primaryproductivity. We conclude that the efficiency of the biological carbon pump in a prolonged open-water perioddepends on the reworking of small, slow sinking material into efficiently sinking fecal pellets or aggregates, andthe occurrence of mixing.

Seasonal patterns of vertical flux in the northwestern Barents Sea under Atlantic Water influence and sea-ice decline