Collaborative Research: Sensitivity of Walker circulation to CO2 forcing during the late Pliocene as an analogue for future climate change

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The proposed study will produce new measurements and simulations of the late-Pliocene (3.3 – 2.58 million years ago) to determine how the Pacific Walker Circulation responds to a warmer climate. The Pacific Walker Circulation is a key feature of the climate system; it impacts temperature and rainfall worldwide, with important socioeconomic consequences. The late Pliocene is an attractive target for understanding sensitivity of Pacific Walker Circulation to changes in atmospheric carbon dioxide concentrations because it features biome distributions, geography, and topography that are similar to the present-day. Carbon dioxide concentration decreased from roughly today’s level during the mid-Piacenzian (3.3 – 3.0 million years ago) to around the preindustrial level during the early-Pleistocene (2.58 million years ago), coincident with (and perhaps driving) the expansion of Northern Hemisphere ice sheets. The study will produce new geochemical data (sedimentary leaf wax isotope data from both western and eastern sides of the tropical Pacific) and will develop water isotopologue tracking enabled Earth System Model simulations to investigate Pacific Walker Circulation sensitivity to late-Pliocene changes in carbon dioxide concentrations and ice sheets. The products will contribute to the existing archives of Pliocene Earth System simulations and observations, providing a community resource for future research and education. A collection of educational activities at high school, undergraduate, and graduate level are also planned to train next generation climate scientists. Strengthening of the Pacific Walker Circulation in response to carbon dioxide increase is a common prediction from atmosphere-ocean coupled Earth System Models. Yet, confidence in this prediction is low due to the short duration of instrumental records, which only chronicle a narrow range of transient climate responses to carbon dioxide increase. This project aims to test model predictions of changes in Pacific Walker Circulation during the late-Pliocene with measurements of deuterium concentrations of sedimentary leaf wax from both western and eastern sides of the tropical Pacific. The team will develop a series of water isotopologue tracking enabled Earth System Model simulations and leaf wax records to understand 1) whether a weaker Pacific Walker Circulation existed during the mid-Piacenzian; 2) what is the sensitivity of Pacific Walker Circulation to carbon dioxide decline during the late-Pliocene; and 3) if the early-Pleistocene glacial expansion strengthened the Pacific Walker Circulation.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.