Collaborative Research: Evaluating Snowlines Across the Tropics - The geomorphic imprint of tropospheric cooling and drying during the Last Glacial Maximum

该奖项的全部或部分资金来自《2021年美国救援计划法案》(公法117-2)。地球科学的一大未解之谜是，为什么全球气候在冰期和间冰期之间振荡，冰期是北美和北欧，数千米厚的冰盖横跨北美和北欧，间冰期是地球变暖，大陆冰盖限制在非常高的纬度。由于全球气候系统的综合性质，要解开这一谜团，需要了解气候系统要素在冰期和间冰期之间过渡期间发生变化的时间顺序，以及跨纬度气候变化的幅度。该项目将利用新出现的遥感数据集，包括高分辨率卫星图像和数字地形，处理热带纬度气候变化的严重程度。具体地说，研究人员将使用遥感数据重建整个热带地区以前的冰川范围，那里的冰川仅限于高海拔山脉难以到达的高地。这项研究将产生一个全球一致的数据集，这将允许测试关于地球低纬地区在最后一次冰川时期冷却了多少，以及热带变化如何影响主要气候重组的假设。该项目将在很大程度上依赖一组本科研究人员，并将与美国冰钻计划合作制作公共教育材料。方法方法基于这样一个认识，即过去全球气候系统的变化可能会影响山脉的地形。这一现象最明显的例子之一是冰川下的侵蚀模式改变了山谷。冰川只存在于温度足以常年结冰的地方，所以如果冰川在侵蚀和沉积地貌中留下了以前范围的迹象，那么就有可能计算出与这些冰川相关的冰冻线的位置。通过创建一个关于精心挑选的地区的热带冰川范围的全球数据集，该项目将实现三个目标：1)对上一次冰川期热带冰冻线的下限作出全球估计；2)利用热带冰川系统(哥斯达黎加)的“典型范例”数值模拟，评估年度冰冻线与热带冰川海拔之间的关系；3)确定上一次冰川期的流失率(温度随海拔变化)是否更陡峭。实现这些目标将促进对为什么全球气候在地球最近的地质历史中受到周期性变化的理解。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).One of the great unsolved mysteries of Earth science is why the global climate oscillates between glacial periods, when multi-kilometer thick ice sheets spread across North America and northern Europe, and interglacial periods, when the Earth is much warmer and continental ice sheets are restricted to very high latitudes. Due to the integrated nature of the global climate system, unlocking this mystery requires knowledge of the chronologic order in which elements of the climate system change during transitions between glacial and interglacial periods and the magnitude of climate changes across latitudes. This project will leverage new and emerging remotely sensed datasets, including high-resolution satellite imagery and digital topography, to address the magnitude of climate changes in the tropical latitudes. Specifically, the researchers will use remotely sensed data to reconstruct former glacial extents throughout the tropics, where glaciers were restricted to the hard-to-reach highlands of high-elevation mountains. The research will produce a globally consistent dataset which will allow the testing of hypotheses about how much the Earth’s low latitudes cooled during the last glacial period, and how tropical changes play into major climate reorganizations. The project will rely heavily on a team of undergraduate researchers and will collaborate with the U.S. Ice Drilling Program to produce public educational material.The methodological approach is based on the realization that past changes in the global climate system can imprint on the topography of mountains. One of the clearest examples of this phenomenon is the transformation of mountain valleys by erosional patterns beneath glaciers. Glaciers only exist where temperatures are cold enough for year-round ice, so if glaciers leave telltale signs of their former extents in erosional and depositional landforms, then it is possible to calculate the position of the freezing line associated with these glaciers. By creating a global dataset of tropical glacial extents in carefully selected areas, the project will achieve three goals: 1) produce a global estimate of the lower bound of the tropical freezing line during the last glacial period 2) use numerical modeling of a “type example” tropical glacial system (Costa Rica) to evaluate the relationship between the annual freezing line and the elevation of glaciers in the tropics and 3) determine whether the lapse rate (change in temperature with elevation) was steeper during the last glacial period. Achieving these goals will advance the understanding of why the global climate has been subject to cyclic variations during Earth’s recent geologic history.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.