Non-Technical Abstract Understanding mechanisms that caused rapid global climate changes in the past is a key problem in paleoclimate research, and is critical for evaluating impacts of ongoing and future climate change. In particular, the role of the tropics in climate shifts remains poorly understood. This grant will provide funding to the University of Minnesota at two campuses: Duluth and Twin Cities, in order to recover a drill core from Lake Chalco, on the southern outskirts of Mexico City. These lake sediments have the potential to provide a half-million year record of North American climate. The core from Lake Chalco is directly relevant to one of the most densely populated urban centers on our planet, Mexico City, home to ~20 million people. The project includes plans to increase public scientific literacy and engagement, building on existing programs in Mexico (museums and mobile classrooms) and Minnesota ("Flyover Country" mobile app), and to organize workshops for local K-12 teachers. A robust plan for evaluation of Broader Impacts is included. This project will contribute to the training of the next generation of geoscientists through the inclusion of students and postdoctoral researchers in the drilling project. This project will foster ties among scientific communities in the U.S., Europe and Mexico, both during drilling and continuing scientific investigations of the Chalco Basin. While the focus of this proposal is recovery of an environmental record, other groups have interest in utilizing the core or the boreholes for a range of studies including volcanic history and hazards, seismic monitoring and earthquake hazard modeling, as well as hydrological monitoring and teaching tools. No funding is provided for these related projects in the current grant.
This grant provides funding to recover a drill core from a >350m lacustrine sedimentary sequence contained in the Lake Chalco basin on the southern outskirts of Mexico City in the Basin of Mexico. These sediments have the potential to provide a >500,000 year record of North American climate. This will be a unique climate archive that could develop into the "type sequence" for paleoclimate studies in North America. Chalco is well suited for reconstruction and investigatation of interannual through orbital-scale variations in the North American Monsoon (NAM) and hydrologic variations of the neotropics. Ongoing work indicates that the system records environmental responses to both Milankovitch- and millennial-scale climate forcing. In order to evaluate the relative role of low latitudes in initiating and propagating abrupt global climate changes, information regarding the geographical distribution, patterns and timing of abrupt changes in the tropics is still needed, particularly records to help define the nature of variability in the Intertropical Convergence Zone (ITCZ). Precipitation over the Chalco Basin is determined by the position of the ITCZ and the strength of the NAM. Long-term (orbital) variations in the position of the ITCZ follow insolation. However, Holocene paleoclimatic records show an antiphase pattern in precipitation intensity between the tropical core of the NAM and its northern margins in response to ocean forcing (e.g. Atlantic Meridional Overturn, AMO, and Pacific Decadal Oscillation, PDO). A record from the Chalco basin can be compared with existing long term records to the North and to the South to determine if this antiphase relationship to AMO and PDO forcing existed in earlier interglacials.