Gas measurements (N2, O2, Ar, CO2, CH4, N2O) of Camp Century and GRIP debris-rich ice.

Ice cores from Camp Century (77° 10' N; 61° 08' W) and GRIP (72° 34’N; 37° 37’W) were sampled and the Niels Bohr Institute in 2021 and 2023. Measurements of gas composition (N2, O2, Ar, CO2, CH4, N2O) were performed on 72 samples at the Université Libre de Bruxelles (Brussels, Belgium) using a custom-made system using a Thermo Scientific™ TRACE™ 1310 Gas Chromatograph. The system measured N2, O2 and Ar with a thermal conductivity detector and CO2 and CH4 with a flame ionization detector. Gas extraction was done under vaccum with melting/refreezing.A measurement of gas species in a sample (nmeasured) was corrected for the blank (nblank), the correction factor (CF), and the analytical bias (AB) as follows: ncorrected = (nmeasured - nblank) / (CF * AB) For O2, Ar and CH4, the blanks were under the limit of detection (LOD) and were, therefore, not considered in the correction. The N2 and CO2 blanks were 4.10× 10-7 ± 3.36 × 10-7 and 1.02 × 10-8 ± 1.14 10-8 mol. The CF is estimated as 0.81 ± 0.03 or 0.72 ± 0.01, depending on the line configuration. The AB is 1.06 ± 0.03, 1.06 ± 0.03, 1.05 ± 0.03, 0.86 ± 0.06 and 1.10 ± 0.04 for N2, O2, Ar, CO2, and CH4 , respectively. Uncertainties were propagated using standard error-propagation formulas, explicitly accounting for the covariance between dependent variables.See Ardoin et al. (submitted at The Cryosphere) for the complete method.