d13CH4 data are measured using the system described in:Schmitt, J., B. Seth, M. Bock, H. Fischer, "Online technique for isotope and mixing ratios of CH4, N2O, Xe and mixing ratios of organic trace gases on a single ice core sample", Atmospheric Measurement Techniques, 7/8, 2645-2665, 2014, doi:10.5194/amt-7-2645-2014All data are free of krypton interference during the mass spectrometric analysis. For details see:Schmitt, J., B. Seth, M. Bock, C. van der Veen, L. Möller, C. J. Sapart, M. Prokopiou, T. Sowers, T. Röckmann, H. Fischer, "On the interference of Kr during carbon isotope analysis of methane using continuous-flow combustion-isotope ratio mass spectrometry", Atmospheric Measurement Techniques, 6/1, 1425-1445, 2013, doi:10.5194/amt-6-1425-2013