Major oxide concentrations of individual glass tephra shards from tephra deposits in the Greenland TUNU2013 [78.04°N/33.88°W] and Summit2023 [72.6°N/38.3°W] ice cores. Deposits analysed are (i) TUNU2013_58.04-58.14m, (ii) Summit2023_180.52-108.69m, and (iii) Summit2023_108.22-108.37m. 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. Sample ID, sample depth (m), sample age (Year CE), tephra name (if known), source volcano, and normalised oxide values are provided.