This pilot project addresses reconstruction of the timing and extent of mountain glacier fluctuations in the Brooks Range of Alaska through the Holocene, including the Holocene thermal maximum. Specifically, this project will collect data to test the hypothesis that factors other than summer insolation are required to explain major centennial-scale changes in the extent of mountain glaciers in the North American Arctic. Previous glacial-geologic studies in the Brooks Range, which relied on lichenometry, concluded that glaciers reached their inter-glacial maximum during the mid-Holocene, about 5 ka. This result is unexpected because the decrease in summer insolation due to orbital forcing during the second half of the Holocene was most pronounced at high latitude. If summer insolation were the primary control on ice extent, then glaciers in the Brooks Range would have reached their maximum extent late during the Little Ice Age (19th century), as they did in the southern part of Alaska. The PI suspects that the seasonal duration of sea-ice cover over the adjacent Arctic Ocean influences the availability of moisture to generate snow during transitional seasons.
This study builds on the PI?s recent success at generating records of Holocene glacier activity using proglacial lake sediments and cosmogenic 10Be dating of Holocene moraine boulders elsewhere in Alaska. It combines 10Be dating of middle and late Holocene moraines with lake coring to generate a well-dated record of glacier variability through the Holocene. The geochronology of lacustrine sediments will be based on a suite of radioisotopes, and the PI will search for cryptotephras as part of a circum-arctic search for Holocene marker beds.
