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

这项研究的目的是确定夏季变暖驱动的冰撤退和融水生产的签名重建的行为，坚持在西北缅因州在最后一个冰河时代结束的冰帽。通过绘制和测定冰川地貌记录缅因州冰帽衰退的模式和时间，以及根据海洋沉积物地球化学重建来自缅因州海湾腐烂冰帽的融水通量，研究人员将评估这个冰帽系统是否与格陵兰冰芯中记录的突然气候变化一致波动，或者它是否在北大西洋stadial事件中撤退，反映了夏季变暖，因此具有强烈的季节性。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解释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态的理解。整体研究工作将为本科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，该公园是该地区最高的山脉卡塔丁的所在地，也是阿巴拉契亚小径的北方末端。研究人员将与巴克斯特公园管理局密切合作，以创新的方式教育公众了解该地区交织在一起的冰川和气候历史及其更大的全球背景。具体目标包括开发3D打印的景观模型，这些模型将与公园场地的教育标语一起沿着展示。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。最后一个冰河时代的结束以一系列壮观的突然气候振荡为特色。在北大西洋地区，冰芯记录了“stadial”间隔之间的突然转换，例如“Heinrich Stadial 1”（HS 1;约18，000 - 14，700 kyr ago）和“新仙女木”（YD; ~ 12，800 - 11，600 kyr ago），其特征是寒冷的年平均温度，以及介于两者之间的Bølling-Allerød 'interstade'（B-A; 14，700 - 12，800 kyr ago），其特征是年平均温度较高。然而，北大西洋区域新出现的证据表明，由于表层海洋淡化和海冰形成，格陵兰冰芯年平均温度的特征可能反映了在stadials期间极端季节性的事件，严重的海冰引起的冬季冷却掩盖了夏季变暖的不同趋势。由于冰川对夏季温度高度敏感，因此，在最后一个冰河时代结束时的冰川变化记录可用于评估季节性在气候突变中的作用。为了检验季节性假设，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帽的垂直变薄和横向退缩，以及融水释放到缅因州海湾的相对模式。制图将得到最近获得的高分辨率激光雷达高程数据的帮助，陆地年代学将得到冰川地貌10 Be表面暴露测年和湖泊沉积物14 C测年的支持。有孔虫痕量金属测量将与δ 18 O配对，以重建进入缅因州湾的融水通量。这项工作的结果将被用来确定是否或不冰川冰消退期间HS 1，然后稳定在B-A时间，预测的季节性假设和一致的模式，在北大西洋沉积物中登记的表面清新。冰川和融水重建将作为GFDL地球系统模型套件的指标，用于测试北大西洋季节循环对夏季大气变暖和淡水通量的响应，提供数据-该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准。

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.