Downward vertical flux of particulate organic carbon (POC) and nitrogen (PON) in the northern Barents Sea during August 2018, Nansen Legacy cruise 2018707 J/C 1-2

Samples for sinking mass flux of particulate organic carbon (POC) and nitrogen (PON) 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. Between 250-1000ml were filtered onto pre-combusted 0.7µm GF/F filters (Whatman, combusted for 7h at 450°C) for the analysis of POC and PON. The filters were then packed in combusted aluminium foil and stored at -20°C. In the lab, the filters were dried for 24h at 60°C and subsequently acid-fumed in HCl for 24h to remove all inorganic carbon. Afterwards, they were dried once again for 24h at 60°C, packed into tin capsules and measured with a CHN elemental analyzer (CE440, Exeter Analytical).