Data were collected as part of the DiatomARCTIC project during the Multidisciplinary Arctic Program - Last Ice sampling campaign (82.576 N 62.471 W), 7-23 May, 2018. The bottom 10 cm of ice samples were collected during this time from neighbouring first-year and multi-year sea ice floes, from which the following parameters were determined: chlorophyll a, exopolymeric substances, ice algal taxonomic composition, oxygen-based net community production and bulk-ice nitrate, nitrite and phosphate concentrations. All samples were melted without dilution and were processed by K Campbell. This work is a contribution to the Diatom ARCTIC project (NE/R012849/1; 03F0810A), part of the Changing Arctic Ocean program, jointly funded by the UKRI Natural Environment Research Council and the German Federal Ministry of Education (BMBF) and Fisheries and Oceans Canada (DFO) Science and the Marine Productivity Laboratory Program. The Multidisciplinary Arctic Program (MAP) - Last Ice is funded by Fisheries and Oceans Canada (DFO) Science in support of Tuvaijuittuq Marine Protected Area (MPA). Additional support was provided by Polar Continental Shelf Program (PCSP, Project 10718) and the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Funds to CM and CHSR.

Persistent organic pollutant concentrations in artificial sea ice experiments at the Roland von Glasow Air-Sea-Ice Chamber (RvG-ASIC) at the University of East Anglia, UK. Experiments involved investigating chemical contaminant behaviours during sea ice formation and melt in order to assess possible exposure risk to sea ice biota. Funding was provided by: NERC ENVISION Doctoral Training Centre (NE/L002604/1). NERC and the German Federal Ministry of Education and Research (BMBF) funded Changing Arctic Ocean program EISPAC project (NE/R012857/1). British Antarctic Survey Collaboration Voucher. EUROCHAMP-2020 Infrastructure Activity under grant agreement (No 730997).

Perfluoroalkyl substances (PFAS) concentrations in artificial sea ice experiments at the Roland von Glasow Air-Sea-Ice Chamber (RvG-ASIC) at the University of East Anglia, UK. Experiments involved investigating chemical contaminant behaviours during sea ice formation and melt in order to assess possible exposure risk to sea ice biota. NERC ENVISION Doctoral Training Centre (NE/L002604/1). NERC and the German Federal Ministry of Education and Research (BMBF) funded Changing Arctic Ocean program EISPAC project (NE/R012857/1). British Antarctic Survey Collaboration Voucher. EUROCHAMP-2020 Infrastructure Activity under grant agreement (No 730997).

Samples of snow, sea ice, seawater (0.5 m and 5 m depths) and meltponds were collected from two ice-covered stations located in the Barents Sea (81 N), during the "Nansen Legacy Q3" summer cruise of the Norwegian research vessel Kronprins Haakon on 26-28 August 2019. Perfluoroalkyl substances (PFAS) concentrations, salinity and stable oxygen isotopes were measured in all samples to determine sources and environmental fate of PFAS during late summer. NERC ENVISION Doctoral Training Centre (NE/L002604/1). NERC and the German Federal Ministry of Education and Research (BMBF) funded Changing Arctic Ocean program EISPAC project (NE/R012857/1). The Nansen Legacy research is funded by the Research Council of Norway (# 276730).