Collaborative Research: Geological constraints on the disappearance of the Laurentide Ice Sheet

劳伦泰德冰原曾经覆盖了北美大陆的大部分地区。在地球最近的地质历史中，它在寒冷时期生长和膨胀，在温暖时期收缩。今天，美国最后的遗迹是巴恩斯冰帽，位于巴芬岛中部。虽然在LIS比现在大得多的时候跟踪它的大小相对简单，但限制LIS最小值的大小和频率更具挑战性，但可以提供一个长期的背景，以评估巴恩斯冰盖目前的小状态。对于这个项目，研究人员将使用新的尖端地质技术来拼凑LIS达到当前尺寸的频率。该团队将由一位早期职业生涯的西班牙裔地球科学家领导，该项目将培养一名博士和两名本科生。调查人员将参加向公众开放的机构开放日，并通过机构实习项目招募本科生参与。了解过去的温暖期及其对冰冻圈的影响，有助于将现代的变暖和冰川消亡置于更长期的背景下。它是地球上最具活力的冰盖，在第四纪经历了多次大陆尺度的扩张和收缩。在陆地和海洋环境中发现了过去冰盖最大值的证据，但间冰期冰盖的最小范围在很大程度上是未知的。巴恩斯冰帽是美国最后遗留下来的遗迹，在末次盛冰期（~27- 20ka）曾经覆盖了北美大陆的大部分地区。研究人员将测量巴恩斯冰盖沿线最近暴露的基岩中的多种宇宙核素（铍-10、碳-14、氖-21、铝-26和氯-36），以量化在间冰期期间，LIS/巴恩斯冰盖达到现代规模的频率和持续时间。他们将使用一种新的野外方法，该方法依赖于浅层基岩岩心（而不是表面样本），并将其与具有不同半衰期的多种宇宙形成核素的库存相结合，以量化第四纪暴露的总时间和基岩表面由于冰的消退而暴露的埋藏时间。结果将与最近格陵兰冰盖项目2 （GISP2）钻孔下的宇宙生成核素测量结果进行比较，后者表明格陵兰冰盖在第四纪期间多次几乎完全消融。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。

The Laurentide Ice Sheet (LIS) once covered much of the North American continent. It grows and expands during cold periods and contracts during warm periods in Earth's recent geological past. Today, the last remaining vestige of the LIS is the Barnes Ice Cap, located on central Baffin Island. While tracking the size of the LIS at times when it was significantly larger than today is relatively straightforward, constraining the size and frequency of LIS minima is much more challenging but can provide a long-term context in which to evaluate the current small state of the Barnes Ice Cap. For this project, the investigators will use new, cutting-edge geological techniques to piece together how often the LIS reaches its current dimensions. The team will be led by an early-career Hispanic geoscientist, and the project will train one doctoral and two undergraduate student. The investigators will participate in institutional open houses that are available to the public and recruit undergraduate student participation through institutional internship programs. Knowledge of past warm periods and their effect on the cryopshere can help place modern warming and glacier demise in a longer-term context. LIS is Earth's most dynamic ice sheet having undergone repeated continental-scale expansions and contractions through the Quaternary. Evidence for past ice-sheet maxima is found in terrestrial and marine settings, yet the minimum extent of the LIS during interglaciations is largely unknown. The Barnes Ice Cap, the last remaining vestige of LIS, once covered much of the North American continent during the Last Glacial Maximum (~27-20 ka). The investigators will measure multiple cosmogenic nuclides (Beryllium-10, Carbon-14, Neon-21, Aluminum-26, and Chlorine-36) from recently exposed bedrock along the Barnes Ice Cap to quantify how frequently and for how long the LIS/Barnes Ice Cap achieves its modern dimensions during interglaciations. They will use a new field method that relies on shallow bedrock cores (rather than surface samples), which will be combined with the inventory of multiple cosmogenic nuclides with different half-lives, to quantify total Quaternary exposure and burial durations of bedrock surfaces just now being exposed by receding ice. Results will be compared to recent cosmogenic nuclide measurements from beneath the Greenland Ice Sheet Project 2 (GISP2) borehole that suggest the Greenland Ice Sheet nearly completely deglaciated on several occasions through the Quaternary.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.