CAREER: Mechanisms of Holocene Rainfall Change in the Northern Tropical Americas

Rainfall patterns in Central America and northern South America are changing as global climate warms, and are associated with disease outbreaks such as Dengue fever and agricultural losses from drought and flooding. The shifts in rainfall have previously been attributed to migration of the Intertropical Convergence Zone (ITCZ), a band of clouds and rain around the equator that tracks the Sun north and south through the seasons. However, it is becoming clear that the observed rainfall patterns can not be fully explained by ITCZ migration. Drivers of the change in rainfall are key uncertainties in future climate projections in this region and, consequently, the projected impacts on human livelihood and safety. This project will use sediments collected from lakes in Guatemala and Venezuela to reconstruct rainfall through the last 10,000 years by measuring the hydrogen isotope ratios of leaf wax molecules, which originate from the surrounding vegetation and reflect the local rainfall. These data will be synthesized with other climate datasets, and the spatial pattern in rainfall and isotopes will be used along with climate models to investigate the contributions of a variety of atmospheric phenomena. The foundation of this research project is investigation of the rainfall patterns in Earth's climate zones. These foundations map to many of the Missouri grade 6-8 learning standards, for which science curriculum resources are scarce. This project will partner with teachers to identify needs and co-develop, field test and improve curriculum, and disseminate materials across the Midwest. The goals of this project are to reconstruct Holocene hydroclimate and vegetation change in the Central America, northern South America (CANSA) region with leaf waxes from six previous collected and dated sediment cores; synthesize the multiple proxy records from these cores to identify spatiotemporal patterns in centennial, millennial and Holocene variability; analyze new and existing model simulations for the dynamics that drive rainfall changes; and compare the data and model simulations to identify mechanisms of rainfall change in the Holocene. The Broader Impacts are to develop grade 6-8 climate science lesson plans in partnership with teachers and disseminate the resources through the Midwest Climate Collaborative's educator network and design a lab for an undergraduate class. 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.