Permafrost and climate change at Herschel Island (Qikiqtaruq), Yukon Territory, Canada

Herschel Island, in the southern Beaufort Sea, is dominantly a glacier ice thrust feature composed of ice-rich, perennially frozen sediments. Climate data are available for Herschel Island from 1899 to 1905 and 1995-2006. Air temperatures at Herschel Island are similar to sites on the adjacent mainland. Late winter snow depth is only about 20 cm, or half the depth on the mainland, and local topography defines the sites of annually recurring snowdrifts. Near-surface ground temperatures, thaw depths, and ground ice contents have been investigated over a 750-m transect leading up Collinson Head, the easternmost part of the island. The ground temperature profile to 42-m depth indicates recent warming of permafrost because the temperature decreases with depth. The temperature at 15-m depth is -8.0 degrees C, the same as the annual mean temperature at 1-m depth at windswept sites along the transect. A simulation of the ground thermal regime, calibrated with local ground properties, equilibrated with the climate of 1899-1905, and driven by the climate of the region during the 20th century reproduces the present ground temperature profile and the annual temperature cycle for 1-m depth at windswept sites. The model indicates that the mean annual temperatures at the top of permafrost and at 20-m depth have increased by 2.6 and 1.9 degrees C, respectively, since 1899-1905, and the perturbation in ground temperature has reached about 120-m depth. Active layer thickness measured in the terrain types studied on Herschel Island is about 55 cm, 15 to 25 cm greater than field data from these units collected in 1985.