Fig. 1. Stratigraphy and geochemistry of shards found in NGRIP1 and NEEM-2011-S1⁶ cores.

QUB-1819c is a shard potentially corresponding to a Japanese volcano (see Supplementary Note 1) (QUB stands for Queen’s University Belfast). a Schematic diagram of the NGRIP1 ice core. b Total alkali versus silica (TAS) diagram⁶⁰. c Additional major oxide bi-plots for glass shards. Only samples for which analytical totals exceeded 90 % and those that might represent a tephra population are shown. Shards in sample T7 were measured by scanning electron microscope energy dispersive spectroscopy (SEM-EDS); all other shards were measured by wavelength dispersive spectroscopy (WDS). Gray shading characterizes the previously reported range of ME glass geochemistry for both proximal and distal deposits^6,9,61,62. Tephra populations in T3 and T7 may correspond to fallout from Mt. Rainier eruptions (Supplementary Note 1). d Location of Mt. Baekdu and NGRIP1 core.