Glacio-geomorphic constraints on the climate history of the high, arid Chajnantor Plateau, subtropical northern Chile

该项目将调查阿塔卡马沙漠东部边界极端干旱的亚热带地区冰川形成的时间、原因和后果。一项初步研究的结果表明，智利北部亚热带高地安第斯山脉壮观的查南托高原过去曾存在覆盖200平方公里的冰帽，那里的降雪量太少，不足以形成今天的冰川冰。这些新的结果提出了几个耐人寻味的问题：安第斯山脉这一干旱地区的冰川有多广泛？与该地区其他干旱和潮湿的记录相比，冰川形成的时间如何？发展和维持这些冰川需要在降水和大气环流方面有哪些变化？冰川、冰缘和与冰川相关的河流侵蚀过程在干旱环境下的景观演变中的相对重要性是什么？解决这些问题是该项目的目标，该项目将沿着三个主要方面进行：1)冰川地貌测绘和年代测定，2)冰川数值模拟，以及3)气候模拟。这项研究的主要组成部分是建立查南托高原及其邻近的安第斯山脉、阿尔蒂普罗和阿塔卡马沙漠地区的严格地貌年代学，特别是包括以北约70公里处的塔蒂奥间歇泉地区。这项工作的重点将放在冰川沉积和相关特征上。该地区的岩石允许可靠地测量原位产生的宇宙成因同位素，如10Be、26Al和36Cl。这使得对冰川、反复无常的冰川和冰川抛光的基岩进行测年，不仅可以描述冰川最大扩张的时期，还可以描述更详细的冰川退缩历史。冰川模拟的主要目的将是估计作为古气候指标的平衡线高度和冰川质量平衡的历史。特别是，它将被用来评估需要多少降水才能维持野外地区的大型冰体。反过来，这将通过建立任何拟议的气候变化机制必须满足的标准来指导大气建模工作。大气模型实验和诊断将被用来检验气候学假说，这些假说可以解释在冰川时期智利亚热带安第斯山脉所需的降水量增加。高分辨率区域模式将在现代控制运行和LGM情景下运行，以涵盖大约30年。冰川的历史和调节它的气候机制在高纬度地区被相对较好地记录下来，但热带和亚热带的冰川历史就不那么有说服力了。在S 18度到S 27度之间的亚热带安第斯山脉目前没有冰川，即使在海拔6公里以上的山脉上，但显示出过去冰川活动的证据。这一地区的山脉很容易就冷到足以维持今天的冰川，但降雪量太少了。该项目将确定冰川最后出现的时间，以及当时维持冰川所需的额外降雪量。这一信息是了解当时大气环流，即气候，为该地区带来更多水分的不同之处的重要线索。因此，这项研究将为亚热带地区由于气候特殊变化而产生的湿和干模型提供重要的约束。换句话说，了解安第斯山脉干旱地区的气候历史有助于预测气候变化对干旱亚热带地区水资源变异性的影响。此外，人类占领研究区和邻近的阿塔卡马沙漠的历史与该地区的水历史有关，这项研究将有助于解决这一问题。这个项目既是国际性的，也是跨学科的。它将建立智利查南托高原“科学保护区”的更多科学用途，许多天文天文台都在那里运作。它还将与智利大学的地球科学家建立工作关系。此外，该项目的论文和演示文稿将在大气科学和地貌学之间的文献中建立正式的联系。该项目由地貌学和土地利用动力学计划和国际科学与工程办公室支持。

This project will investigate the timing, causes, and consequences of glaciation in an extremely arid subtropical landscape on the eastern boundary of the Atacama Desert. Results of a pilot study demonstrate the past existence of an ice cap covering over 200 square kilometers on the spectacular Chajnantor Plateau in the high, subtropical Andes of Northern Chile, where far too little snow falls to form glacial ice today. These new results raise several intriguing questions: How extensively glaciated was this arid part of the high Andes? How does the timing of the glaciation compare with other records of aridity and moistening from the region? What changes in precipitation and atmospheric circulation were required to develop and maintain these glaciers? What is the relative importance of glacial, periglacial, and glacially-related fluvial erosion processes in landscape evolution in arid settings? Addressing these questions is the goal of this project, which will proceed along three main fronts: 1) mapping and dating of glacial landforms, 2) numerical glacier modeling, and 3) climate modeling. The major component of the research is to establish a rigorous geomorphologic chronology for the Chajnantor Plateau and immediately adjacent areas of the Andes, Altiplano and Atacama Desert, specifically including the Tatio Geysers area about 70 km to the north. The brunt of the work will focus on glacial deposits and related features. The rocks of the area permit reliable measurement of in-situ produced cosmogenic isotopes such as 10Be, 26Al, and 36Cl. This allows dating of moraines, erratics, and glacially polished bedrock to describe not only periods of maximum ice expansion but also more detailed histories of glacial retreat. The primary purpose of the glacier modeling will be to estimate the history of equilibrium line altitude and glacier mass balance as a paleoclimate proxy. In particular, it will be used to evaluate how much more precipitation is needed to sustain large ice bodies in the field area. This, in turn, will guide atmospheric modeling efforts by establishing a criterion that must be met by any proposed climate change mechanism. Atmospheric model experiments and diagnostics will be used to test climatological hypotheses that could explain the required precipitation increases in the subtropical Chilean Andes during glacial times. High-resolution regional models will be run to encompass approximately 30 years in both a modern control run and in an LGM scenario. Broader significance.The history of glaciation and the climate mechanisms that modulate it are relatively well documented at high latitudes, but tropical and subtropical glacial histories are less robust. The subtropical Andes between 18 degrees S and 27 degrees S are presently unglaciated, even on mountains higher than 6 km, but show evidence of past glacial activity. The mountains in this region are easily cold enough to sustain glaciers today, but simply receive far too little snowfall. This project will establish when glaciers were last present and the amount of additional snowfall needed at that time to sustain them. This information is an important clue to understanding what was different about atmospheric circulation, i.e., climate, at that time to bring more moisture to the region. Therefore, this study will provide an important constraint on models of wetting and drying in the subtropics as a result of specific changes to climate. In other words, understanding the history of climate in the dry parts of the Andes contributes to predicting the impacts of climate change on water resource variability in arid subtropical areas. Additionally, the history of human occupation of the study area and the adjacent Atacama Desert are tied to the history of water in the region, which this study will help to resolve. This project is both international and cross-disciplinary in scope. It will establish additional scientific uses of the Chilean "science preserve" of the Chajnantor Plateau, where many astronomical observatories operate. It will also establish a working relationship with geoscientists at Chilean universities. Moreover, the papers and presentations resulting from this project will create a formal link in the literature between atmospheric sciences and geomorphology.This project is supported by the Geomorphology and Land Use Dynamics Program and the Office of International Science and Engineering.