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

这个试点项目解决重建的时间和范围内的山区冰川波动的布鲁克斯范围阿拉斯加通过全新世，包括全新世热最大。具体而言，该项目将收集数据，以检验以下假设，即需要夏季日照以外的因素来解释北美北极地区山地冰川范围的重大百年尺度变化。以前对布鲁克斯山脉的冰川地质研究依赖于地衣测量法，得出的结论是，冰川在全新世中期达到了间冰期的最大值，大约5 ka。这一结果是出乎意料的，因为在全新世后半期，由于轨道强迫，夏季日射量的减少在高纬度地区最为明显。如果夏季日照是冰的主要控制因素，那么布鲁克斯山脉的冰川将在小冰期（世纪）晚期达到最大程度，就像阿拉斯加南部一样。PI怀疑，在邻近的北冰洋海冰覆盖的季节性持续时间的影响，在过渡季节的水分生成雪的可用性。最近，美国科学家利用冰前湖沉积物和阿拉斯加其他地方全新世冰碛石的宇宙成因10Be年代测定成功地记录了全新世冰川活动。它结合了10Be测年的中期和晚期全新世冰碛湖取芯，以产生一个良好的记录，通过全新世冰川的变化。湖相沉积物的地质年代学将以一套放射性同位素为基础，PI将寻找隐火山岩，作为环北极寻找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.