Downward vertical flux of particulate organic carbon (POC) and nitrogen (PON) in the northern Barents Sea during May 2021, Nansen Legacy cruise 2021704 Q2

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 May 2021 as part of the Nansen Legacy project (cruise 2021704, Q2). 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 12 to 27 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. At selected stations, single trap cylinders were deployed by divers 1m below the sea ice. 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).