Recent changes in thickness of the Devon Island ice cap, Canada

Long-term rates of thickness change were derived at several spatial scales using a variety of methods for most of the Devon Island ice cap, Nunavut, Canada. Basin-wide thickness change calculations were derived for the accumulation zones of all major drainage basins as the area-averaged volume difference between balance and InSar fluxes at the altitude of the long-term equilibrium line (ELA). Thickness changes for ablation zones were derived as a function of the surface mass balance, flux across the EL and calving flux, averaged across the ablation areas. Average rates of thickness change are near zero in the accumulation zones of the northern and southwestern basins but reach -0.23 +/- 0.11 ma(-1) w.e. in the southeast basin due to dynamic thinning. Thickness changes were also estimated along five major outlet glaciers as a function of flux divergence and net surface mass balance and along the Belcher Glacier by comparing elevation values derived from 1960s aerial photography with those derived from 2005 NASA Airborne Topographic Mapper (ATM) surveys. Ice dynamics have had a significant influence on the pattern of thickness change of all outlet glaciers examined in this study. Volume changes derived from the basin-wide values indicate a net loss of -76.8 +/- 7 km(3) water equivalent from the main portion of the ice cap from 1960 to 1999, contributing 0.21 +/- 0.02 mm to global sea level over this time. This value is similar to 44% greater than previous estimates of volume change based on volume-area scaling methods and surface mass balance alone.