Surface snow samples were collected daily from a Canadian high Arctic location at Eureka, Nunavut (80N, 86W) from the end of February to the end of March in 2018 and 2019. The snow samples were collected at several sites representing distinct environments: sea ice, inland close to sea level, and a hilltop ~600 m above sea level. Ion Chromatography (IC) analysis was performed for most of the snow samples. Snow salinity measurement is mainly for surface snow. Surface ozone was measured at sea level (from the Zero Altitude PEARL Auxiliary Laboratory (0PAL)) and lower tropospheric BrO (0-4 km) was measured by MAX-DOAS instrument (at ~610 m located at the Polar Environment Atmospheric Research Laboratory (PEARL)). This study was supported by the UK NERC Arctic office via two UK-Canada bursary programs: "The role of tundra snowpack chemistry in the boundary layer bromine budget at Eureka, Canada" (2018), and "A second investigation of the role of tundra snowpack chemistry in the boundary layer ''bromine explosion''" (2019). The Eureka MAX-DOAS BrO measurements made at the PEARL Ridge Laboratory by the Canadian Network for the Detection of Atmospheric Change (CANDAC) was primarily supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Space Agency (CSA), and Environment and Climate Change Canada (ECCC).

This dataset includes stable nitrogen isotopes of 1- nitrate in sea water (d15NNO3) from three sites (i.e. Southern Barents Sea, Northern Barents Sea, Greenland Sea) and 2- of bulk tissue (d15Nbulk) and compound specific stable nitrogen isotopes on amino acids (d15NAA) measured in adult harp seals from five sites (i.e. Southern Barents Sea, Northern Barents Sea, Greenland Sea, Labrador shelf, Baffin Island) and in adult ringed seals from two sites (Baffin Island and Canadian Archipelago) in the Arctic and sub-Arctic. The sea water samples for analyses of d15NNO3 were collected in 2017 and 2018 as part as two ARISE cruises (JR16006 and JR17005). The seal samples were collected from 2015 to 2019 as part of Norwegian commercial sealing and student field courses from the University of Tromso in Norway (Northern and Southern Barents Sea, Greenland Sea) and the Inuit subsistence and commercial harvests in Canada (Labrador Sea, Baffin Island, Canadian Archipelago). Analyses of d15NNO3 were carried out at the University of Edinburgh, UK. Analyses of d15Nbulk and d15NAA of seal muscle tissue were carried out at the Liverpool Isotopes for Environmental Research laboratory, University of Liverpool. Results are reported here in standard delta-notation per-mil relative to atmospheric N2. Funding was provided by the ARISE project (NE/P006035/1 and NE/P006310/1), as part of the Changing Arctic Ocean programme, funded by the UKRI Natural Environment Research Council (NERC).