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TRIMLINES AND RECENTLY EXPOSED TERRAIN AS INDICATORS OF RAPID CLIMATIC CHANGE IN THE QUEEN ELIZABETH ISLANDS, ARCTIC CANADA
WOLKEN, GABRIEL Dept. of Earth and Atmospheric Sciences, University of Alberta.
Climate change during the 20th and 21st centuries has resulted in extensive modification of polar regions; this trend is expected to continue as predicted temperature increases in these regions exceed those elsewhere on the globe (IPCC, 2001). Consequently, the Arctic is a key region to investigate and monitor in order to assess both past and present climatic variability. However, because the instrumental record in the Canadian High Arctic extends back only ~50 years, it is essential to investigate other proxy records to determine variability over longer time scales, in order to provide a more meaningful measure of natrual variability, and to function as reference against which modern and future conditions may be compared.
The Queen Elizabeth Islands (QEI), Arctic Canada, represents an area of ~410,000 km2 and contains ~5% of the terrestrial ice found in the Northern Hemisphere (Koerner, 1989). Evidence for a substantial reduction in terrestrial ice cover in the QEI following the Little Ice Age (LIA) (~1600 – 1900 AD), is in many cases indicated by lighter-toned zones that display an abrupt ice-distal margin, extending back to the modern ice mass. These trimlines or so-called “lichen-free zones” also record the former position and maximum extent of perennial snowfields, which mark the position of the former equilibrium-line altitude (ELA). Supervised classification methods were used with orthorectified multispectral imagery (ASTER, 2000-2002; Landsat 5 and 7, 1993-2002) to map trimlines throughout the QEI. Modern ice margins were derived through supervised and unsupervised classification processes of the same imagery, and 1959/60 ice outlines were acquired from the National Topographic Database (NTDB) (provided by Geomatics Canada). Differences revealed between modern and former ELAs, as well as the removal and rapid retreat of former ice masses, serves to substantiate the impact of 20th century warming in the QEI.
IPCC, 2001, Summary for policymakers: Climate change 2001: impacts, adaptation, and vulnerability. Report of Working Group II of the IPCC.
Koerner, R. M., 1989, Queen Elizabeth Islands Glaciers. Geological Survey of Canada.
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