Micrometre-sized volcanic glasses in polar ices and snows

Explosive volcanic eruptions can follow long cycles of activity1, and the material that they inject into the atmosphere may affect the climate2. We report here the discovery of ultrathin micrometre-sized glass shards from such eruptions, extracted from both ancient Antarctic ices and recent snow samples from Greenland, in which they have been well preserved by ‘deep freezing’. When such shards have been preselected using a high-voltage electron microscope, microanalysis of their eight major constituent elements gives new clues about the origin of major volcanic acid fallout previously detected in the cores (including important characteristics of their parent eruptions), and reveals complex volcanic ash layers that could reflect periods of world-wide enhanced volcanicity. Moreover, the very small Reynolds numbers of the micrometre-sized shards make them promising tracers of dust transport processes in the ancient atmosphere.