Collaborative Research: Ice sheet sensitivity in a changing Arctic system - using geologic data and modeling to test the stable Greenland Ice Sheet hypothesis

格陵兰冰盖（GrIS）中有足够的水，如果它融化，将会使大多数沿海城市的海平面显著上升，给社会带来巨大后果。面对冰盖对海平面上升的加速贡献，GrIS将如何适应北极变暖、海冰减少和相关降水模式的变化仍不确定。这是一个令人担忧的问题，因为未来海平面的上升在很大程度上取决于GrIS对北极变化的反应。科学界目前还没有决定是采用在温暖期大幅减少的动态GrIS模式，还是相对稳定的模式，即使在比今天更温暖的时期也是如此。这一建议解决了北极降水增加抵消GrIS在温度升高期间质量损失的想法。研究人员将通过在过去和正在进行的暖期提供北极系统变化和相关GrIS动态的重要新信息来验证这一点，并采用冰盖建模工作，综合针对过去和未来GrIS模拟的所有新数据。研究人员明确地将多个科学学科结合起来，以更好地了解北极系统的关键组成部分，如降水、温度、海冰覆盖和GrIS质量平衡是如何相互联系的。其结果将对北极系统、GrIS和全球海平面上升的命运具有根本的相关性。本项目将培养6名研究生和1名博士后。跨领域的研究项目与推广计划的范围并行，以开发各种可交付成果，包括开发iBook和公共推广活动。此外，该团队还将参加布法罗和纽约市的公共推广活动，在那里公众和科学家们在一个随意的环境中互动。最后，这项工作与NASA正在进行的任务和NSF的其他项目有协同作用。技术方面：由于最近在数值冰盖模型和格陵兰岛新的冰下地形方面取得的进展，结合精细的野外方法和地质年代学技术，对北极变暖的冰冻圈变化进行协调的跨学科努力的时机已经成熟；格陵兰冰原和海冰构成了北极冰冻圈最大、最关键的组成部分。在气温升高期间，北极降水增加可以抵消GrIS质量损失的假设源于最近的发现，这些发现表明，在间冰期，它可能比预期的更稳定。研究人员将：在全新世中期热极大期（9,000至5,000年前）期间和之后，利用强大的方法将湖泊沉积物地层学与新的亚冰地形学和新的高灵敏度宇宙成因同位素方法相结合，生成新的GrIS边缘重建；从湖泊和海洋沉积物中重建全新世的湿度、温度和海冰条件，并对现有的北极冰芯和其他古气候资料进行先进的综合；并采用由冰缘和气候重建推动的最先进的数值冰盖模型来测试GrIS变化的一系列气候和动态控制。如果这一观点得到支持，那么它将表明在温暖时期GrIS相对稳定。然而，如果该项目提供证据证明GrIS在比现在更温暖的全新世中期大幅退缩，反过来，GrIS对温度的反应比降水变化更敏感，那么结果将支持紧密耦合的冰盖大小-温度联系，反过来，GrIS对海平面上升的近期贡献更大。这两种结果都将对北极系统、GrIS和全球海平面上升的命运产生根本性的影响。

NontechnicalThere is enough water in the Greenland Ice Sheet (GrIS) that, were it to melt, it would raise sea level in most coastal cities significantly with huge consequences for society. In the face of accelerated ice sheet contribution to sea level rise, it remains uncertain how the GrIS will adjust to a warming Arctic, declining sea ice and related changing precipitation patterns. This is a concern, given that future sea level rise is strongly dependent on the GrIS response to arctic change. The scientific community is currently undecided between a model of a dynamic GrIS that becomes greatly reduced during warm periods and a model where it is relatively stable, even through periods warmer than today. This proposal addresses the idea that increased arctic precipitation offsets GrIS mass loss during times of elevated temperature. The researchers will test this by contributing significant new information on arctic system change and related GrIS dynamics during past and ongoing warm periods, and employing an ice sheet modeling effort synthesizing all new data aimed at both past and future GrIS simulations. The researchers explicitly combine multiple scientific disciplines to provide a better understanding of how key arctic system components such as precipitation, temperature, sea-ice cover and GrIS mass balance are interconnected. The results will be of fundamental relevance to the fates of the arctic system, the GrIS and global sea level rise.This project will train six graduate students and one post-doctoral researcher. The cross-cutting research program is paralleled by the scope of the outreach plan, to develop a variety of deliverables, including development of an iBook and public outreach events. In addition the team will participate in public outreach events in Buffalo and New York City, where the public and scientists interact in a casual setting. Finally, this work has synergies with ongoing missions at NASA and other programs within the NSF.TechnicalDue to recent advances in numerical ice sheet models and new sub-ice topography of Greenland, combined with finely-tuned field approaches and geochronologic techniques, the time is ripe for a coordinated, cross-disciplinary effort focusing on cryosphere variability in a warming Arctic; the Greenland Ice Sheet (GrIS) and sea ice constitute the largest, and most critical components of the arctic cryosphere. The hypothesis that increased arctic precipitation can counterbalance GrIS mass loss during times of elevated temperatures stems from recent findings suggesting that it may be more stable than expected during interglacials. The researchers will: generate new GrIS margin reconstructions during and since the mid-Holocene Thermal Maximum (9,000 to 5,000 years ago), with a powerful approach that combines lake sediment stratigraphy with new sub-ice topography and novel high-sensitivity cosmogenic isotope methods; develop new Holocene climate reconstructions of moisture, temperature and sea ice conditions from lake and ocean sediments and an advanced synthesis of existing arctic ice core and other paleoclimate data; and employ state-of-the-art numerical ice sheet modeling fueled by ice margin and climate reconstructions to test a range of climatic and dynamic controls on GrIS change. If the idea is supported, then it would suggest a relatively stable GrIS during warm periods. If, however, this project provides evidence that the GrIS retreated considerably during the warmer-than-present mid-Holocene and in turn, that the GrIS has reacted more sensitively to temperature than to precipitation change, the results would support a tightly coupled ice sheet size-temperature link and in turn, a much greater near-term GrIS contribution to sea level rise. Either result will be of fundamental relevance to the fates of the arctic system, the GrIS and global sea level rise.