Seasonal growth bands in pingo ice

Abstract

Field studies of pingo ice show that alternating clear and bubble bands may grow when water freezes at the top of a subpingo water lens. A study of the banding at one excellent exposure of pingo ice shows that the clear bands probably grew during propagation of the cold winter temperature waves, the bubble bands, from the warmer summer temperature waves. The likely cause for the gradual transitions from clear to bubble bands followed by the abrupt transitions from bubble to clear bands was marked asymmetry of the periodic temperature waves in permafrost overlain by an active layer whose thermal properties varied seasonally. Pingo growth, as determined from the growth of bands, shows good agreement with Stefan's equation where growth varied as the square root of time. Geochemical profiles show no systematic change with depth. Stable-isotope profiles for δ18O and δD show linear trends with depth and a depletion of the heavy isotopes. The co-isotope slope of 7.2 suggests freezing, with the input being impoverished in the heavy isotopes.