NSFGEO-NERC: Collaborative Research: MexiDrill: Developing a 350,000 year record of climate and environmental change in tropical North America

了解过去气候变化的机制是古气候研究中的一个关键问题，对评估当前和未来气候变化的影响至关重要。恰尔科湖（Lake Chalco）的沉积物，就在墨西哥城外，保存着对全球科学界有价值的地质、古环境和古生物学信息，与生活在墨西哥盆地的2000万人直接相关。由于持续的气候变化，预计墨西哥的大部分地区在未来几十年和几个世纪将变得更加干燥；这些人为变化将叠加在气候系统的自然变率上。在墨西哥中部，预测结果普遍指出，由于夏季雨季降水减少和蒸发速率加快，将出现干旱。温度和降水记录的分析将为评价Chalco湖沉积物中保存的气候历史提供一种手段。该项目的结果将有助于更好地了解地球上人口最稠密的城市中心之一的气候和水文平衡。水文平衡至关重要，既影响农业和饮用水，也影响对疾病的脆弱性。这项研究将有助于对墨西哥城地区的火山历史进行更详细的评估，这也将有助于在对过去活动的全面了解的基础上对该地区进行火山危害评估。墨西哥盆地是世界上人口最稠密的地区之一，大型火山爆发产生的沉降物沉积物有可能严重破坏整个城市。该团队将把墨西哥的实地指南整合到“Flyover Country”移动应用程序中，该应用程序将提供英语和西班牙语两种版本。该项目通过让早期至中期职业女性担任重要角色，并通过研究生和博士后研究人员的参与，支持发展一支多元化的、具有全球竞争力的STEM劳动力队伍。为了评估低纬度在引发和传播全球变化中的作用，我们需要有关热带地区突变的地理分布和时间的信息。墨西哥中部是北美热带古气候遗址的地理中心，一份长期而详细的气候记录将增强我们对北美气候中纬度与热带联系的理解。这项NSF-GEO/NERC联合提案的主要科学目标是获得自更新世中期以来北美热带地区气候和生物群过去变化的连续、高分辨率记录。我们将分析墨西哥城南郊Chalco湖盆地最近恢复的约350米湖相沉积层序。Chalco沉积物序列可能提供了35万年的气候和环境变化记录，以及对区域火山活动的显著重建。特别感兴趣的主题包括：1)主要气候模式影响的冰期/间冰期变率，如热带辐合带（ITCZ）和西风带的迁移；2)轨道尺度变率，特别是进动对热带辐合带位置的影响及其对中美洲季风的影响；3)冰期和终止期间的千年尺度变率。在Chalco，受太平洋和大西洋盆地温度变化控制的气团之间的相互作用比其他站点更强，并且由于其高海拔位置，水文气候变化被放大。这将是北美最长的气候、环境和生物群档案之一，而这一地区目前缺乏此类记录。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。

Understanding the mechanisms that caused past climate change is a key problem in paleoclimate research, and is critical for evaluating impacts of ongoing and future climate change. Sediments from Lake Chalco, just outside Mexico City, hold geologic, paleoenvironmental, and paleobiological information of value to the global scientific community, and directly relevant to the 20 million people living in the Basin of Mexico. Much of Mexico is projected to become drier in the coming decades and centuries in response to ongoing climate change; these anthropogenic changes will be superimposed on natural variability in climate systems. In central Mexico projections generally point to drying as a result of decreased rainfall during the summer rainy season and enhanced evaporation rates. Analysis of records of temperature and precipitation will provide a means to evaluate the history of climate preserved in Lake Chalco sediments. Results of this project will contribute to an improved understanding of climate and hydrological balance in one of the most densely populated urban centers on Earth. Hydrological balance is critical, impacting agriculture and drinking water as well as affecting vulnerability to disease. This study will enable more detailed assessment of volcanic history in the Mexico City region, which will also allow development of volcanic hazard assessment for the region that is based on a comprehensive understanding of past activity. The Basin of Mexico is one of the world's most heavily populated areas, and fallout deposits from large explosive eruptions have the potential to significantly disrupt the entire city. The team will incorporate field guides from Mexico into the "Flyover Country" mobile app, which will be available in English and Spanish. The project supports the development of a diverse, globally competitive STEM workforce by including early-to-mid career women in significant roles and through the inclusion of graduate students and postdoctoral researchers. To evaluate the role of low latitudes in initiating and propagating global changes, we need information regarding the geographical distribution and timing of abrupt changes in the tropics. A long and detailed climate record from central Mexico, the geographic center of North American tropical palaeoclimate sites, will enhance our understanding of the mid-latitude to tropical linkages in North American climate. The primary scientific objective of this joint NSF-GEO/NERC proposal is to obtain a continuous, high-resolution record of past changes in climate and biota in the North American tropics since the mid-Pleistocene. We will analyze a recently recovered ~350m lacustrine sedimentary sequence from the Lake Chalco basin on the southern outskirts of Mexico City. The Chalco sediment sequence is likely to provide a 350,000 year record of climate and environmental change, as well as a remarkable reconstruction of regional volcanic activity. Topics of particular interest include 1) glacial/interglacial variability in the influence of major climate modes such as migration of the InterTropical Convergence Zone (ITCZ) and Westerlies, 2) orbital scale variability, particularly the influence of precession on the location of the ITCZ and its influence on the Mesoamerican Monsoon, and 3) millennial scale variability during glacial periods and terminations. Interplay between air masses controlled by temperature changes in the Pacific and Atlantic basins is stronger in Chalco than at other sites, and hydroclimate changes are amplified due to its high altitude location. This will be among the longest archives of climate, environment, and biota from North America, from a region presently lacking such records.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.