Seasonal patterns of vertical flux along an Atlantic-Arctic gradient in the Northern Barents Sea

Abstract

The northern Barents Sea is strongly influenced by sea ice loss and inflow of Atlantic water. This affects the pelagic marine ecosystem, which ultimately has implications for the vertical transport of organic matter to the seafloor. We deployed short-term sediment traps along a revisited transect across a latitudinal gradient through the seasonal ice zone in the northern Barents Sea to compare spatial patterns of vertical flux among four contrasting seasons (August and December 2019, March and May 2021). To characterize the composition of vertical flux, we sampled for particulate organic carbon (POC), Chlorophyll a (Chla), protist abundance and biomass, fecal pellets, stable isotopes, HPLC and highly branched isoprenoids (HBIs). In accordance with previous findings, our results show that POC and Chla fluxes are highest in spring and summer (means of 178 and 159 mg POC mˉ² d‾¹, respectively), and lowest in winter. Spatial variability was highest in spring and strongly dependent on the position of the sea ice edge relative to the location. δ¹³C and δ¹⁵N measurements supported the seasonal character of vertical flux. Our results demonstrate that vertical flux in the Northern Barents Sea is highly variable across seasons and locations and not only determined by seasonal ice zone dynamics, but also by episodic storm events, advected under-ice phytoplankton blooms, and horizontal inflow of Atlantic Water. Studies on the influence of such infrequent processes on vertical flux are limited, although they may have implications for carbon cycling and export in a future Arctic under climate change.