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度干旱的亚热带景观中冰川作用的时间、原因和后果。一项初步研究的结果表明，在智利北部安第斯山脉的亚热带高原上，壮观的查南托高原上过去存在着一个覆盖200多平方公里的冰帽，那里的降雪太少，今天无法形成冰川。这些新的结果提出了几个有趣的问题：安第斯山脉的干旱地区冰川覆盖范围有多广？与该地区的其他干旱和湿润记录相比，冰川作用的时间如何？降水和大气环流的什么变化需要这些冰川的发展和维持？在干旱环境中，冰川、冰缘和与冰川相关的河流侵蚀过程在景观演变中的相对重要性是什么？解决这些问题是这个项目的目标，它将沿着三个主要方面进行：1)冰川地貌的测绘和年代测定，2)冰川数值模拟，以及3)气候模拟。该研究的主要组成部分是为查南托高原和邻近的安第斯山脉、Altiplano和阿塔卡马沙漠建立严格的地貌年代学，特别是包括北部约70公里的Tatio间歇泉地区。这项工作的重点将放在冰川沉积物和相关特征上。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。这使得冰碛岩、不稳定岩和冰川磨光的基岩的年代测定不仅可以描述最大冰扩张时期，还可以描述更详细的冰川退缩历史。冰川模拟的主要目的是估计平衡线高度和冰川质量平衡的历史，作为古气候的代用物。特别是，它将被用来评估需要多少降水来维持野外地区的大型冰体。反过来，这将通过建立任何提出的气候变化机制必须满足的标准来指导大气模拟工作。大气模式实验和诊断将用于测试气候学假设，这些假设可以解释亚热带智利安第斯山脉在冰川时期所需的降水增加。高分辨率区域模型将在现代控制运行和LGM情景下运行大约30年。更广泛的意义。高纬度地区的冰川史和调节冰川史的气候机制的记录相对较好，但热带和亚热带的冰川史则不那么可靠。在南纬18度和南纬27度之间的亚热带安第斯山脉，即使在海拔6公里以上的山上，目前也没有冰川，但显示出过去冰川活动的证据。这个地区的山脉很容易寒冷到足以维持冰川，但降雪太少。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。这些信息是了解当时大气环流（即气候）的不同之处的重要线索，从而为该地区带来了更多的水分。因此，该研究将为气候变化导致的亚热带干湿模式提供重要的约束。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亚热带干旱地区水资源变异的影响。此外，人类在研究区域和邻近的阿塔卡马沙漠的占领历史与该地区的水历史有关，这项研究将有助于解决这个问题。这个项目在范围上是国际性和跨学科的。它将建立智利Chajnantor高原“科学保护区”的额外科学用途，那里有许多天文台。它还将与智利大学的地球科学家建立工作关系。此外，这个项目产生的论文和报告将在大气科学和地貌学之间的文献中建立正式的联系。该项目由地貌与土地利用动力学项目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.