Collaborative Research: Response of the Tropical Pacific to the Abrupt Climate Change Event 8,200 Years Ago

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A catastrophic outburst of glacial meltwater into the Labrador Sea 8,200 years ago disrupted Atlantic Ocean circulation, plunging the North Atlantic region into cold conditions for more than a century and impacting climate globally. Some climate models indicate that the vast tropical rain bands may shift south in response to such a perturbation, which has important implications for understanding how the climate might change in the future if a warming ocean disrupts ocean circulation. Yet few reconstructions of rainfall exist from the tropics that span the 8,2000-year-ago time interval, making it difficult to confirm the model-based predictions. To remedy this data gap this project will reconstruct rainfall changes in the tropical Pacific from chemical variations in lake sediments in Palau and the Galápagos that lie on the northern and southern edges of the modern tropical rain band. The research will include climate model simulations elucidating the rainfall changes expected in Palau and the Galápagos in response to a meltwater addition to the North Atlantic similar in size to that estimated during the 8,200-year-ago event. A workshop will be held for Micronesian high school teachers along with an experiential learning coarse in Kosrae (Micronesia). Students from the University of Washington will work with high school teachers and conduct field exercises and create curricular activities based on their experiences. Rainfall will be reconstructed from hydrogen isotope ratios of the microalgal lipid dinosterol in radiocarbon-dated sediments from lakes in Palau and the Galápagos. Confidence in the regional nature of the hydrogen isotope signals will be achieved through replication of measurements, sediment cores, lakes, and islands. All nine sediment cores, which range in length from 2-15 m, have been collected, and most have initial radiocarbon chronologies. A temporal resolution of 25-40 yr is proposed for the 7,000-9,000-year-ago interval of each core, which ranges in thickness from 50-250 cm. The remainder of the Holocene period in each core will have hydrogen isotope data produced at 250-500-yr resolution in order to place any of the 8,200-yr-ago excursions in the context of the full Holocene. Interpretations of these rainfall reconstructions, including their global context, will be aided by simulations with the isotope-enabled Community Earth System Model forced with realistic meltwater fluxes to the Labrador Sea. Because models diverge widely in their response of tropical Pacific rainfall to freshwater forcing, our rainfall reconstructions will provide a critical benchmark for these models and help constrain the mechanisms by which the tropics respond to abrupt AMOC disruptions.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.