Pilot Project: Reconstructing tropical North American climate with the sedimentary record of Lake Chalco, Mexico

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This project examines a sedimentary sequence from Lake Chalco (Central Mexico) to develop a ~50 kyr record of terrestrial climate variability in the North American tropics. The project uses proxies that reflect hydrological and thermal variability, focusing in particular on the transition from the Last Glacial Maximum to the Holocene. This project is in cooperation with the Autonomous University of Mexico who, in the first phase of a drilling program, recovered a ~100 m drill core. Subsequent drilling may extend this by 100 m, providing a record back to ~300 ka that includes the previous two interglacials. This pilot project focuses on the uppermost 50 m of the core recovered earlier. The analyses include x-ray fluorescence core scanning for major elemental composition at an average resolution of ~20 years through the 50 m section, as well as a series of organic geochemical analyses, including MBT (paleotemperature), biomarker del-D (aridity) and lignins and biomarker del-13C (vegetation response) at ~1000 year resolution since 50 ka. This work provides a 'proof of concept' for this site and a unique level of information on past temperatures and precipitation since mid-MIS 3 in a region where climate records are sparse. The climate record from Chalco should provide insights on regional responses to past changes in coupled climate systems. Recent work in Antarctic ice cores documents significant differences in atmospheric pCO2 and climate change over the Middle Pleistocene (EPICA 2005, Siegenthaler, 2005), but high-resolution continental records spanning this interval are rare globally and absent in North America. The full Chalco record has the potential to provide unique information that fills this critical gap, improving our understanding of our present interglacial and its future course.This project contributes to the training of the next generation of geoscientists through the direct support of graduate and undergraduate students. This study also fosters international collaboration among scientific communities in the U.S. and Mexico; Mexican students will come to the Large Lakes Observatory to work on this project.Broader impacts to the scientific community include a reconstruction of the climate history of central Mexico spanning the past 35 kyr, and a validation of the application of the MBT paleotemperature proxy in lacustrine systems of Mexico. Increasing temperatures predicted by modern global climate change will significantly impact natural systems as well as human populations in the coming century. Gaining a better understanding of climate system processes and how they are reflected in geochemical proxy records can help in modeling future climate trends. Appropriate application of rigorously investigated proxies provides the best information about paleoclimate estimates currently available on timescales beyond the existence of instrumental records.