Methodology:

Environmental samples were collected in the European High Arctic during the "Nansen Legacy Q3" summer cruise of the Norwegian research vessel Kronprins Haakon on 26-28 August 2019.

Sea ice cores (n = 4) at each site were drilled (spaced ~ 1 m intervals) and then immediately cut into horizontal layers (n = 7-10) that were between 0.1 and 0.2 m in length.

Melt ponds samples (n = 3) at each site were collected. Melt ponds were covered by a thin layer of ice, which was removed before sampling water (1 L).

Snow samples (n = 4) at each site were collected above each sea ice core (approximately 0.25 m2).

Seawater samples were collected approximately 20 m from snow and sea ice samples, at 0.5 and 5 m below sea ice.

PFASs were analysed using solid phase extraction (SPE) which took place onboard the ship with further analysis conducted at Helmholtz-Zentrum Hereon, Germany. Stable oxygen isotope and salinity analysis was undertaken at Lancaster University, UK.

Data collection:

PFAS: HPLC-MS/MS, using an HP 1100 LC system (Agilent Technologies, U.S.A.) coupled to an API 4000 triple quadrupole mass spectrometer (AB Sciex, U.S.A.). Analyst Software Version 1.5.

Salinity: Hach HQd40 logger with the CDC401 probe.

Stable isotope: Elementar pyrocube elemental analyzer linked to an Isoprime 100 mass spectrometer).

Data quality:

Mass-labelled chemical standards were used as recovery standards to assess analytical performance.

A 13-point mixed-standard calibration curve was used for quantification.

Sample replicates (n = 7) were used determine analytical method performance.

Method detection limits (MDL) were calculated from laboratory blanks (n = 5; SPE-filtered milliQ water) and field blanks (n = 2; collected washings of field sampling equipment with SPE-filtered milliQ water).