Firn–ice transition-zone features of four polythermal glaciers in Svalbard seen by ground-penetrating radar

Abstract

AbstractDetailed ground-penetrating radar (GPR) surveys on the firn–ice transition zones of Kongsvegen, Nordenskjoldbreen, Hansbreen and Werenskioldbreen, Svalbard, are presented. We discuss features seen in GPR radargrams in all polythermal glaciers down-glacier of the firn line. The firn line of a polythermal glacier in GPR data is easily detected with both 50 and 200 MHz radar. By comparison with satellite images, characteristic patterns of reflection are shown to be caused by superimposed ice, but the reflections from the interface between the superimposed ice and the underlying glacier ice are of unknown origin. Layered reflections within the superimposed ice and firn area are likely from layers of ice lenses and relatively low-density firn in the firn area, and from bubble-rich and bubble-poor ice in the superimposed-ice zone. Dipping foliations in the glacier ice down-glacier of the firn line show that the layered reflections from the firn line are preserved, though in much weaker form, even when the firn has been transformed to solid ice.