LATE HOLOCENE GLACIER FLUCTUATIONS IN THE MACKENZIE AND SELWYN MOUNTAINS, NORTHWESTERN CANADA

Over the past 40 years, tropospheric warming in the western Canadian Arctic has been nearly double that of the global average. The amplitude of this warming shows that this region is responding sensitively to climate change, but at present almost nothing is known about past glacier and climate fluctuations in the region’s interior mountain ranges. To address this knowledge gap, we visited alpine sites in the Mackenzie and Selwyn mountains. Most glaciers in the region are small cirque and valley glaciers ranging in size from 0.1 to 10 km². Analysis of aerial photographs, satellite imagery and helicopter surveys reveal readily observable glacier deposits consisting of a single group: unvegetated lateral and terminal moraines that demarcate extents that were approximately 50% greater than they are today. For some glaciers, these deposits consist of two closely-spaced moraine crests. Equilibrium line altitude (ELA) reconstructions from three glaciers, whose moraines were sampled for cosmogenic nuclide dating, suggest ELA depressions of 85 m +/- 20 m, compared to modern reconstructed ELA’s. We collected 22 samples from moraine boulders for beryllium-10 surface exposure dating to establish chronologic control on glacier fluctuations. We await analysis on 15 samples; however, seven samples from three moraines yield a median age of 700 +/- 54 a. Preliminary results suggest that mountain glaciers in the Mackenzie and Selwyn mountains reached their maximum Holocene extents 200-400 years earlier than most glaciers in southwestern Canada, which fits the general trend of southward decrease of Holocene moraine ages in western Canada. However, expanded resolution of the timing of maximum glacier extents in this region is needed to validate these claims. Our data elucidate the nature and timing of late Holocene glacier activity in northwestern Canada and lengthen the reconstructed climate record of this sensitive region.