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

这一试点项目涉及重建阿拉斯加布鲁克斯山脉至全新世的山脉冰川波动的时间和程度，包括全新世的最高温度。具体地说，该项目将收集数据来检验这一假设，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百年来的重大变化。布鲁克斯山脉以前的冰川地质研究依赖于地衣测量学，得出的结论是，冰川在全新世中期达到冰间最大值，约为5ka。这一结果是出乎意料的，因为在全新世的后半段，由于轨道强迫而导致的夏季日照强度的下降在高纬度地区最为明显。如果夏季的日照是对冰川范围的主要控制，那么布鲁克斯山脉的冰川应该在小冰期(19世纪)晚些时候达到最大程度，就像它们在阿拉斯加南部所做的那样。PI怀疑邻近北冰洋海冰覆盖的季节性持续时间影响了过渡季节产生雪的水分的可用性。这项研究建立在PioS最近成功地利用前冰川湖泊沉积物产生全新世冰川活动记录和对阿拉斯加其他地方的全新世冰川巨石进行宇宙成因10Be测年的基础上。它将全新世中晚期冰川10Be测年与湖泊取芯相结合，生成了全新世冰川变化的准确日期记录。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将搜索隐语，作为环北极全新世标志层搜索的一部分。

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.