Is the high-elevation region of Devon Ice Cap thickening?

Abstract

Devon Ice Cap, Nunavut, Canada, has been losing mass since at least 1960. Laser-altimetry surveys, however, suggest that the high-elevation region (>1200m) of the ice cap thickened between 1995 and 2000, perhaps because of anomalously high accumulation rates during this period. We derive an independent estimate of thickness change in this region by comparing ∼40 year mean annual net accumulation rates to mean specific outflow rates for 11 drainage basins. The area-averaged rate of thickness change across the whole region is within error of zero (0.01 ± 0.12 m w.e. a-1), but two drainage basins in the northwest are thickening significantly, and two basins in the south are thinning significantly. The laser-altimetry observations are biased towards the drainage basins where we find thickening. Recent changes in the rate of accumulation or the rate of firnification cannot explain the observed thickening, but decreased ice outflow, due to the penetration of Neoglacial cooling to, and subsequent stiffening of, the basal ice, may provide an explanation. Thinning in the south may result from increased ice outflow from basins in which fast flow and basal sliding extend above 1200 m.