LATEST PLEISTOCENE AND HOLOCENE GLACIER VARIABILITY OF THE ARRIGETCH PEAKS, ALASKA

The sensitivity of high latitude glaciers in the Brooks Range, Arctic Alaska, presents a unique opportunity to study centennial- and millennial-scale variability within the Arctic climate system over the past ~15,000 years. However, the Holocene glacial record in the Brooks Range is dated mainly by lichenometry, which is relatively imprecise. To address the gap in present knowledge, we apply cosmogenic ¹⁰Be exposure dating for the first time to the moraines and glacially scoured terrain of the Arrigetch Peaks area, south-central Brooks Range. Four cirque glaciers and their moraines were investigated during summer 2012. Guided by lichenometry, we sampled Neoglacial moraine boulders and paired samples of perched erratic boulders on glacially eroded bedrock beyond the Neoglacial moraines. The lichenometric results indicate moraine building events at approximately 1800, 3500, and 5000 yr B.P. ¹⁰Be ages collected from the neoglacial moraines, as well as valley deglaciation samples outboard of the neoglacial moraines, are pending at the time of this writing and will be presented. Finally, comparative photographs taken during the summer of 2012 add to previous photos taken in 1911, 1962, and 1979, establishing a 101 year record of glacial change. These photographs show initial rapid retreat followed by decelerating recession of Arrigetch glaciers up to the present. The use of lichenometry, ¹⁰Be dating, and the photographic record provides a powerful combination for reconstructing glacial fluctuations from the latest Pleistocene to the present. We expect that these results will constrain multiple glacial advances over the past 5,000 years more precisely than lichenometry, and reinforce our understanding of glacial behavior during Neoglaciation in the Brooks Range. In addition, samples beyond the Neoglacial moraines will constrain the latest Pliestocene deglaciation and may shed light on the presence or absence of a significant readvance during the Younger Dryas.