Stable isotopic composition (d13C and d15N) of sinking particulate matter measured from short-term sediment traps in the northern Barents Sea during August 2019, Nansen Legacy cruise 2019706 Q3

Samples for carbon and nitrogen isotopic composition of sinking organic matter 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 2019 as part of the Nansen Legacy project (cruise 2019706, Q3). 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 18 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 carbon and nitrogen stable isotopic composition. The filters were then packed in combusted aluminium foil and stored at -80°C. In the lab, the filters were dried for 24h at 60°C and subsequently packed 5x9 tin capsules (Elemental Microanalysis), and then measured with a Thermo Fisher Scientific EA IsoLink IRMS System, which consists of a Thermo Fisher Scientific Flash Elemental Analyzer and a Thermo Fisher Scientific DeltaV Isotope Ratio Mass Spectrometer. Samples were analyzed at the CLIPT stable isotope biogeochemistry lab at UiO, funded by the Research Council of Norway through its Centers of Excellence funding scheme #223272 (Centre for Earth Evolution and Dynamics). Standards for isotopic ratios for carbon and nitrogen were Vienna PeeDee belemnite and air, respectively. Alanine (JALA, Fischer Scientific) was used for internal quality assurance with an analytical precision of δ¹³CVPDB = -20.59 +- 0.05 ‰ (n = 47 runs) and δ15NAIR = -3.16 +- 0.10 ‰ (n = 57), respectively. L-glutamic acid (JGLUT, Fischer Scientific) and glycine (POPPGLY, Fischer Scientific) were used as internal reference material. Internal references and quality assurance for δ13CVPDB were calibrated against calcium carbonate (NBS19) and lithium carbonate (LSVEC) with consensus values 1.95 ‰ and -46.6 ‰, respectively, and for δ15NAIR against L-glutamic acid (USGS40 and USGS41) with consensus values -4.52 ‰ and 47.57 ‰, respectively.