Nitrate isotope measurements from CTD niskin depth profiles from cruise PS100 in the Fram Strait during July-August 2016.

Nitrate isotope samples were collected onboard the R/V Polarstern in the Fram Strait from 18th June - 6th September 2016 as part of the Geotraces transect with samples analysed by the Changing Arctic Ocean programme. Seawater samples were filtered inline from the Niskin bottles, and frozen at -20degC until analysis on land. Samples were measured for δ¹⁵N-NO3 and δ¹⁸O-NO3 of nitrate using the Denitrifier method and bacterial strain P. aureofaciens. Samples were corrected using international reference standards IAEA-N3 and USGS-34 and an internal standard of North Atlantic Deep Water was run to check for inter-run comparability. Final values were calculated using the correction scheme of Weigand et al., (2016) with reproducibility of 0.1 and 0.3‰ for δ¹⁵N-NO3 and δ¹⁸O-NO3 respectively.