P2C2: Collaborative Research: The Role of Seasonality in Abrupt Climate Change - a Test by Reconstructing Fluctuations of a Late-Glacial Ice Mass in Eastern North America

这项研究旨在通过重建最后一个冰河时代末期缅因州西北部持续存在的冰盖的行为，来确定夏季变暖驱动的冰退缩和融水产生的特征。通过绘制冰川地貌并确定年代，记录缅因州冰盖衰退的模式和时间，以及根据海洋沉积物地球化学重建缅因湾消融冰盖的融水通量，研究人员将评估该冰盖系统是否与格陵兰冰芯记录的突然气候变化一致波动，或者它是否在北大西洋固定时期消退。反映了夏季变暖和强烈的季节性。通过这些冰川和融水变化的地质重建，研究人员将采用一个地球系统模型来评估变暖引起的融水通量对北大西洋地区季节性的影响。澄清季节性在气候突变中的作用将对破译气候突变的起源具有重要意义，并将有助于加深对导致冰河时代结束的全球气候动力学的理解。整个研究工作将为本科生和研究生阶段的下一代科学家提供实地培训和教育，并与缅因州的巴克斯特州立公园合作，深入加强公众参与。巴克斯特州立公园是该地区最高的山峰卡塔丁的所在地，也是阿巴拉契亚山道的北端。研究人员将与巴克斯特公园管理局（Baxter Park Authority）密切合作，以创新的方式向公众宣传该地区冰川和气候交织的历史，以及更大的全球背景。具体目标包括开发3d打印景观模型，这些模型将与公园场地的教育标语牌一起展示。研究人员还将与一个新媒体团队合作，开发一个信息丰富的智能手机应用程序，可以在整个公园使用。最后一个冰期的结束以一系列壮观的气候突变为特征。在北大西洋地区，冰芯记录了“平均”间隔的突变，如“Heinrich stadial 1”（HS1; ~18,000 - 14,700 kyr ago）和“Younger Dryas”（YD; ~12,800 - 11,600 kyr ago），其特征是年平均温度较低，而其间的Bølling-Allerød“interstade”（B-A; 14,700 - 12,800 kyr ago）的特征是年平均温度较高。然而，北大西洋地区新出现的证据表明，由于海洋表面的新鲜和海冰的形成，格陵兰冰芯的年平均温度特征可能反映了冬季极端季节性的事件，海冰引起的冬季严重降温掩盖了夏季变暖的不同趋势。由于冰川对夏季气温高度敏感，因此，在最后一个冰河期结束期间的冰川变化记录可用于评估季节性在气候突变中的作用。为了验证季节性假设，研究人员将结合地貌测绘、陆地冰川地质年代学和海洋沉积物地球化学来重建缅因州冰盖的垂直变薄和侧向退缩，以及融水释放到缅因湾的相对模式。测绘将借助最近获得的高分辨率激光雷达高程数据，陆地年代学将通过冰川地貌的10Be表面暴露年代和湖泊沉积物的14C年代来支持。有孔虫痕量金属测量将与δ18O配对，以重建流入缅因湾的融水通量。这项工作的结果将用于确定冰川冰是否在HS1期间消退，然后在B-A期间稳定，正如季节性假设所预测的那样，并与北大西洋沉积物中记录的地表更新模式相一致。冰川和融水重建将作为GFDL一套地球系统模型的度量标准，用于测试北大西洋季节周期对夏季大气变暖和淡水通量的响应，为气候突变的季节性假设提供数据模型测试。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。

This research aims to determine the signature of summer-warming-driven ice retreat and meltwater production by reconstructing the behavior of an ice cap that persisted in northwestern Maine during the end of the last ice age. By mapping and dating glacial landforms documenting the pattern and timing of Maine ice-cap recession, as well as by reconstructing meltwater fluxes from the decaying ice cap in the Gulf of Maine on the basis of marine sediment geochemistry, the researchers will evaluate whether this ice cap system fluctuated in concert with the abrupt climate changes as registered in Greenlandic ice cores, or whether it retreated during the North Atlantic stadial episodes, reflecting summertime warming and hence intense seasonality. Informed by these geological reconstructions of glacier and meltwater change, the researchers will employ an Earth System Model to evaluate the effects of warming-induced meltwater fluxes on seasonality in the North Atlantic region. Clarifying the role of seasonality in abrupt climate change will have important implications for deciphering the origins of abrupt climate change and will help to hone understanding of the global climate dynamics that brought the ice age to an end. The overall research effort will provide field-based training and education for the next generation of scientists at the undergraduate and graduate level, as well as in-depth enhanced public engagement in cooperation with Maine’s Baxter State Park, home of Katahdin, the highest mountain in the region and the northern end of the Appalachian Trail. The researchers will work closely with the Baxter Park Authority on innovative ways to educate the public about the intertwined glacial and climatic history of the region and its greater global context. Specific objectives include developing 3D-printed landscape models, which will be displayed along with educational placards at park venues. The researchers will also collaborate with a New Media team to develop an informative smartphone app that can be used throughout the park.The termination of the last ice age featured a spectacular series of abrupt climate oscillations. In the North Atlantic region, ice cores recorded abrupt switches between ‘stadial’ intervals, such as ‘Heinrich Stadial 1’ (HS1; ~18,000 – 14,700 kyr ago) and the ‘Younger Dryas’ (YD; ~12,800 – 11,600 kyr ago), which were characterized by cold mean-annual temperatures, and the intervening Bølling-Allerød ‘interstade’ (B-A; 14,700 – 12,800 kyr ago) that was characterized by warmer mean-annual temperatures. However, emerging evidence in the North Atlantic region indicates that, because of surface-ocean freshening and sea-ice formation, the signature of mean-annual temperatures in Greenlandic ice cores may reflect episodes of extreme seasonality during stadials, with severe sea-ice-induced winter cooling masking a divergent trend of summertime warming. Because glaciers are highly sensitive to summer temperatures, records of glacier change during the termination of the last ice age can therefore be used to evaluate the role of seasonality in abrupt climate change. To test the seasonality hypothesis, the researchers will use a combination of geomorphic mapping, terrestrial glacial geochronology, and marine sediment geochemistry to reconstruct both the vertical thinning and lateral retreat of the Maine ice cap and the relative pattern of meltwater release into the Gulf of Maine. Mapping will be aided by recently acquired high-resolution LiDAR elevation data, and the terrestrial chronology will be underpinned by 10Be surface-exposure dating of glacial landforms and 14C dating lacustrine sediments. Foraminiferal trace-metal measurements will be paired with δ18O to reconstruct meltwater fluxes into the Gulf of Maine. The results of this work will be used to determine whether or not glacial ice receded during HS1 and then stabilized during B-A time, as predicted by the seasonality hypothesis and consistent with the pattern of surface-freshening registered in North Atlantic sediments. Glacier and meltwater reconstructions will serve as metrics for a GFDL suite of Earth system models employed to test the response of the North Atlantic seasonal cycle to imposed summer atmospheric warming and freshwater fluxes, affording a data-model test of the seasonality hypothesis for abrupt climate change.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.