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

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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.