Firn Pack Changes on White Glacier, Axel Heiberg Island, Nunavut

Abstract

The near-surface processes and variability within the firn pack of Arctic glaciers are a significant source of uncertainty in estimating future glacier responses to climate warming. This study provides the first characterization of the firn pack of White Glacier, Axel Heiberg Island, Nunavut, and an analysis of recent firn pack changes (2013-2019). Utilizing ground penetrating radar (GPR) surveys the firn pack thickness, extent, and associated topographic controls on firn distribution were determined. Two methods of GPR analysis were tested in this study. The first followed the traditional approach of conducting visual interpretation of radargrams to identify zones of backscatter associated with firn. The second is a proposed new methodology that uses average backscatter values from each radar return as a proxy indicator of firn presence in the subsurface. The results of these two approaches showed that the firn pack on White Glacier has reduced in extent, and reductions in average backscatter values suggest that the density of the firn has increased in the near surface. Overall, the long-term firn area decreased in extent by 3.96 km2 (10% of the total glacier area) between 2013 and 2018. Rates of surface lowering were determined using dual-frequency GPS surveys. For spring 2018 to spring 2019 the rate was -0.165 ± 0.29 m a-1 in the accumulation area, likely driven by the near surface densification. The potential for average backscatter values to provide information about near surface snow water equivalence is also explored.