Evolution of Pliocene-Pleistocene climate and vegetation in the Tropical Andes

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The Pliocene epoch, 5 to 2.5 million years ago, is often cited as the last time global climate resembled that of the present day. While the concentrations of atmospheric CO2 were comparable to those of today, Earth's mean temperature was likely ~3 degrees centigrade warmer, which raises questions about how sensitive our climate system is to CO2 changes. Additionally, there is considerable debate about how these warmer temperatures affected the tropics, including precipitation and vegetation. This project reconstructs environmental changes occurring in the tropical Andes of Colombia over the past 5 million years to test the relationships between global climate transitions, tropical environmental change, and mountain uplift. This initiative enhances Inter-American collaboration among US and Colombian scientists, fosters the career of a minority graduate student, an early career faculty, undergraduate research assistants from low-income families and minority groups, and inspires underprivileged children in elementary and middle schools through bilingual activities in collaboration with the CU Museum of Natural History.This project constitutes the first integration of biomarker-based climate and vegetation records in lake sediment and outcrops by reconstructing continental climate variability in the tropics since the late Miocene. Surface temperatures, vegetation, and hydrological changes are constrained using branched GDGTs, plant waxes, and their stable isotope composition, in addition to existing and new pollen records preserved in sediment from the Sabana de Bogota (Colombia): (a) the Funza II (~70 ka to ~3 Ma) sediment core from the extinct Funza Lake; (b) outcrop samples of Late Miocene-Pleistocene fluvial and lacustrine deposits; and (c) Late Miocene-Early Pliocene fluvial deposits at low-elevation sites. Additionally, contemporary soil samples along the wet and dry flanks of the Eastern Cordillera will be used to produce a modern proxy calibration. This study provides a foundation to determine whether the tropics were warmer when mid and high-latitude regions were warm. Such a record will fill a hole in reconstructions of past climate in the tropics since the Pliocene and will provide a comprehensive climatic framework to better interpret vegetation changes in the tropics.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.