Secondary standards of Lipari, BCR-2Ga, ML3B-G, StHS6/80-G, and Old Crow for major element oxide tephra glass analyses obtained from individual glass shards from samples TUNU2013_58.04-58.14m, Summit2023_180.52-108.69m, and Summit2023_108.22-108.37m in the Greenland TUNU2013 [78.04°N/33.88°W] and Summit2023 [72.6°N/38.3°W] ice cores. Normalised analytical data (totals to 100%) and the original analytical totals are reported (before normalisation) all as weight %. Data was obtained using electron probe micro-analysis (EPMA) at the University of Bern, Switzerland and the University of St Andrews, UK.