Arctic melt and summer temperature during past warm periods: a new ice core proxy

北极冰川融化对当地社区、生态系统和基础设施以及全球海平面产生深远影响。过去冰融化的长期记录有助于科学家更好地了解导致冰融化的过程，例如夏季气温和冰中吸收阳光的烟灰和其他颗粒的浓度。特别是，研究过去的温暖期很重要，因为它们为我们未来的气候提供了潜在的类似物。重建过去表面熔体的一种方法是通过视觉检测无气泡层。然而，过了大约5000年，融化层就不再可见了，因为冰层被冰流大大变薄，而且气泡溶解在冰晶中。该奖项支持开发一种新技术来重建北极冰芯过去的融化，并将该技术应用于研究格陵兰岛和阿拉斯加北极冰芯过去的温暖期。该奖项支持俄勒冈州立大学的一名研究生，为STEM（科学、技术、工程和数学）劳动力做出贡献。研究人员将为来自服务不足地区的中学生和高中生开发有关冰芯和气候变化的课程材料，在俄勒冈州立大学举办两次STEM教师研讨会，并支持俄勒冈州农村社区的学生俱乐部。冰川冰芯保存了过去地表融化的记录，可用于了解过去因气候强迫（无论是自然的还是人为的）而导致的融化强度变化。传统上，研究人员通过视觉检测无气泡层来重建冰芯过去的表面融化。不幸的是，这种方法不适用于老冰和/或深冰，因为在这些地方，融冰层已无法直观地识别。研究人员将采用一种新的冰芯代表表面融化强度：氙/氮比。在没有融水再冻结的情况下，冰样品中的氙/氮比值反映了大气比值。然而，由于氙的高溶解度，在表面熔体存在的情况下，氙/氮比变得强烈富集。研究者将使用这个代理来解决四个重要的科学问题：(1)北极全新世热极大期的时间和强度是什么；(2)末次间冰期格陵兰岛融化的程度和幅度；(3)在长时间尺度上，北极融化的驱动因素是什么；(4)与过去一万年相比，北极目前的融化速度如何。研究者建议测量Renland和GISP2冰芯（都来自格陵兰岛）和Mt. Hunter冰芯（来自阿拉斯加）。氙/氮熔体代理将被校准以重建当地的夏季温度。拟议的工作使用现有的冰芯样本，不涉及北极实地考察。该奖项支持俄勒冈州立大学的一名研究生，为STEM（科学、技术、工程和数学）劳动力做出贡献。研究人员将为来自服务不足地区的中学生和高中生开发有关冰芯和气候变化的课程材料，在俄勒冈州立大学举办两次STEM教师研讨会，并支持俄勒冈州农村社区的学生俱乐部。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Glacier ice melt in the Arctic has profound impacts on local communities, ecosystems and infrastructure, and global sea level. Long-term records of past ice melt help scientists better understand the processes that contribute to ice melt, such as summer air temperatures and the concentration of soot and other particles in the ice that absorb sunlight. In particular, past warm periods are important to study because they provide potential analogs for our future climate. One method to reconstruct past surface melt is through visual detection of bubble-free layers. However, beyond approximately 5000 years, the melt layers are no longer visible because the ice layers get strongly thinned by ice flow and because the air bubbles dissolve into the ice crystals. This award supports the development of a new technique to reconstruct past melt in Arctic ice cores and the application of this technique to study past warm periods in Arctic ice cores from Greenland and Alaska. The award supports a graduate student at Oregon State University, contributing to the STEM (Science, Technology, Engineering and Mathematics) workforce. The researchers will develop lesson materials on ice cores and climate change for middle and high school students from underserved regions, host two STEM teacher workshops at OSU, and to support student clubs across Oregon rural communities.Glacier ice cores preserve a record of past surface melting that can be used for understanding past variability in melt intensity in response to climate forcing - either natural or anthropogenic. Researchers have traditionally reconstructed past surface melt in ice cores using visual detection of bubble-free layers. Unfortunately, this method does not work for old and/or deep ice, where melt layers can no longer be visually identified. The investigator will apply a new ice core proxy for surface melt intensity: the xenon/nitrogen ratio. In the absence of refrozen meltwater, the xenon/nitrogen ratio in ice samples reflects the atmospheric ratio. However, because of the high solubility of xenon, the xenon/nitrogen ratio becomes strongly enriched in the presence of surface melt. The investigator will use this proxy to address four important scientific questions: (1) what is the timing and magnitude of the Holocene Thermal Maximum in the Arctic; (2) what is the extent and magnitude of Greenland melt during the Last Interglacial period; (3) what are the drivers of Arctic melt on long time scales; and (4) how do current melt rates in the Arctic compare to the last 10,000 years. The investigator proposes measurements on the Renland and GISP2 ice cores (both from Greenland), and the Mt. Hunter ice core (from Alaska). The xenon/nitrogen melt proxy will be calibrated to reconstruct local summer temperature. The proposed work uses existing ice core samples and does not involve Arctic fieldwork. The award supports a graduate student at Oregon State University, contributing to the STEM (Science, Technology, Engineering and Mathematics) workforce. The researchers will develop lesson materials on ice cores and climate change for middle and high school students from underserved regions, host two STEM teacher workshops at OSU, and to support student clubs across Oregon rural communities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.