Downward vertical flux of protist cells and biomass in the northern Barents Sea during August 2018, Nansen Legacy cruise 2018707 JC 1-2

Samples for protist cell and biomass flux were collected with short-term drifting sediment traps between 75° and 85°N in the northern Barents Sea with R/V Kronprins Haakon in August 2018 as part of the Nansen Legacy project (cruise 2018707, JC 1-2). High-density bottom water was collected at the station and filtered (Whatman GF/F 0.7µm), and then filled into the trap cylinders (KC Denmark, aspect ratio >6) prior to their deployment. Afterwards, the sediment traps were deployed with 2 or 4 cylinders at each depth (30, 40, 60, 90, 120, 200m) for a duration between 22 to 25 hours. Depending on the sea ice conditions, the sediment traps were deployed in open water, anchored to a sea ice floe or within an ice lead. Upon retrieval, the content of the cylinders from each depth was pooled and stored at 4°C in dark until further analyses. For protist examination, a subsample of 100ml was transferred to a brown glass bottle and fixed with a mixture of glutaraldehyde-lugol. Protists were identified to the lowest possible taxonomic level in accordance with the World Register of Marine Species (WoRMS) and counted under an inverted light microscope (Nikon Eclipse TE-300 and Ti-S) using the Uthermöhl method (Edler & Elbrächter, 2010; Utermöhl, 1958). Protist carbon biomass flux was calculated from abundances using established geometric relationships for biovolume conversion (Hillebrand et al., 1999) and biovolume-to-carbon conversion factors (Menden-Deuer & Lessard, 2000).