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

该奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。地球科学最大的未解之谜之一是，为什么全球气候在冰川期和间冰期之间摇摆不定。冰川期是指数公里厚的冰盖遍布北美和北欧的时期，间冰期是指地球变暖得多，大陆冰盖局限于高纬度地区的时期。由于全球气候系统的整体性，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变化的时间顺序，以及各纬度气候变化的幅度。该项目将利用新的和新兴的遥感数据集，包括高分辨率卫星图像和数字地形，来解决热带纬度地区气候变化的规模。具体来说，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，那里的冰川仅限于难以到达的高海拔山区高地。这项研究将产生一个全球一致的数据集，它将允许测试关于地球低纬度地区在最后一个冰川期冷却了多少的假设，以及热带变化如何影响主要的气候重组。该项目将在很大程度上依赖于一个由本科生组成的研究团队，并将与美国冰层钻探计划合作，制作公共教育材料。方法方法是基于这样一种认识，即过去全球气候系统的变化会对山脉的地形产生影响。这种现象的一个最明显的例子是冰川下的侵蚀模式对山谷的改变。冰川只存在于温度低到足以全年结冰的地方，因此，如果冰川在侵蚀和沉积地貌中留下了它们以前的范围的迹象，那么就有可能计算出与这些冰川相关的冻结线的位置。通过在精心挑选的地区建立热带冰川范围的全球数据集，该项目将实现三个目标：1)对末次冰期热带冰川线下界进行全球估计；2)利用一个“类型示例”热带冰川系统（哥斯达黎加）的数值模拟来评估热带地区年冰川线与冰川高程之间的关系；3)确定末次冰川期的递减率（温度随高程的变化）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。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 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.