Fig. 3: Ice core tephra occurrences relative to measured sulfate concentration.

Sulfate (SO₄²⁻) concentration measured by ion chromatography of 1–3 cm subsamples taken from across the volcanic peak in ice cores (a) NEEM (Greenland) and (b) EDC (Antarctica). In both panels, dashed lines indicate samples where one or more tephra glass shards were found and analyzed for major oxide geochemistry. Subsamples containing tephra populations that match LCY geochemistry are indicated by red stars and red shading. Light-red shading and stars show single-shard occurrence before the main population that correlates with LCY in the NEEM ice core. Additional samples where tephra is correlated to a known source (see Supplementary Fig. 4) are indicated by black shapes: Circle = Grímsvötn, Iceland⁵⁵; Cross = Eastern Aleutian Arc⁵⁶; Triangle = Marie Byrd Land, Antarctica⁵⁴. Bracketed numbers indicate how many shards of correlated composition were measured. Smaller peaks in NEEM SO₄²⁻ concentration on either side of the largest peak (LCY) can be attributed to the events identified by these tephra populations.