Collaborative Research: P2C2--Reconstructing South American Monsoon Sensitivity to Internal and External Forcing: Reconciling Models and Tree-ring Proxies in the Central Andes

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The potential Broader Impacts include the potential for better understanding the South American monsoon, for filling in sparse hydroclimate records, and for fuller understanding climate variability. Collaboration with South American colleagues is planned as is extensive student involvement.This project aims to employ classical dendrochronological techniques to generate new tropical tree-ring chronologies that are annually resolved and absolutely dated. Radiocarbon measurements (14-Carbon) will ensure accurate dating assessments. Thus, successful tree species will be selected to improve the 14-Carbon curve for the Southern Hemisphere. The resulting tree-ring series will be used to reconstruct past climate variability and regional to large--scale atmospheric dynamics for the last several centuries. The specific aims of the project are to improve understanding of: (1) the spatiotemporal variability of the South American summer monsoon (SASM); (2) long-term interactions between El Niño-Southern Oscillation (ENSO) and the SASM; and (3) the impact of volcanic forcing on past hydroclimate of the tropical Andes.The research aims to provide significant advances in the science of tropical dendrochronology bydeveloping a tree-ring network for the tropical Andes in Peru and Bolivia, a region with exceedingly scarce coverage of high-resolution terrestrial paleo-records. While tree rings have been extensively used in temperate climates, the tropics remain relatively unexplored due to the difficulty, in particular, of identifying consistent wood layers (tree rings) corresponding to seasonal or annual growing periods. The Central Andes are an ideal region for overcoming these difficulties, due to the pronounced precipitation seasonality and diverse forests.The tropical Andes are a hotspot for biodiversity and its geographic position makes it extremely vulnerable to climate change. It also contains nearly all the tropical glaciers on the globe, and recent, widespread glacial retreat is causing a rapid decline in hydrological reserves. This decline, in combination with increasing water demand due to population growth and economic expansion poses an enormous challenge for water availability, biodiversity and food security. The complex topography of the Andean Cordillera leads to a climate that is characterized by strong zonal and vertical precipitation gradients. Moisture influx from the tropical Atlantic Ocean and the Amazon basin is modulated by the SASM and ENSO. The scientific understanding of this variability is challenged by the scarcity of long instrumental observations, which also limits the ability to constrain uncertainties in future climate change projections over this region.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.