Characteristics and Possible Source of a 1479 A.D. Volcanic Ash Layer in a Greenland Ice Core

A microparticle concentration peak in a GISP2 ice core contains volcanic glass shards of rhyolitic composition that correspond in age to the 1479-1480 A.D. Mt. St. Helens Wn eruption. These glass shards are compositionally similar to the Wn tephra and constitute 83% of the total particle population. The shards are very coarse-grained (up to 40 μm diameter), suggesting rapid transport from their source to Greenland. A major sulfate peak in the ice occurs approximately 4 months after deposition of the glass shards. This difference in depositional timing suggests primarily tropospheric transport of the ash and stratospheric transport of the sulfate aerosol. Large-scale climatic perturbations following this eruption were evidently negligible. Glaciochemical seasonal indicators suggest a late-fall to early-winter 1479 A.D. eruption.