Arctic mountain glacier response to past global changes - a pilot study from the Brooks Range, Alaska

该试点项目旨在重建阿拉斯加布鲁克斯山脉在全新世期间（包括全新世热最大值）山地冰川波动的时间和范围。具体来说，这个项目将收集数据来检验一个假设，即需要夏季日照以外的因素来解释北美北极山区冰川范围的百年尺度变化。以前在布鲁克斯山脉进行的冰川地质研究依赖于地衣测量，得出的结论是冰川在全新世中期（约5 ka）达到了间冰期的最大值。这一结果是出乎意料的，因为全新世后半期轨道强迫导致的夏季日照减少在高纬度地区最为明显。如果夏季日照是控制冰川面积的主要因素，那么布鲁克斯山脉的冰川在小冰河期（19世纪）晚期达到了最大值，就像阿拉斯加南部一样。PI怀疑邻近北冰洋海冰覆盖的季节性持续时间会影响过渡季节产生雪的水分的可用性。这项研究建立在PI？他最近成功地利用前冰川湖沉积物和阿拉斯加其他地方全新世冰碛巨石的宇宙成因10Be定年，生成了全新世冰川活动的记录。它结合了全新世中期和晚期冰碛的10Be定年和湖泊取心，得出了全新世冰川变化的准确年代记录。湖泊沉积物的地质年代学将以一套放射性同位素为基础，PI将寻找隐层，作为环北极搜索全新世标志层的一部分。

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.