COLLABORATIVE RESEARCH: TRACKING PCO2, REGIONAL CLIMATE, AND VEGETATION CHANGE DURING MID-MIOCENE GLOBAL WARMING THROUGH THE EXCEPTIONAL PLANT RECORDS OF THE PACIFIC NORTHWEST, USA

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Seventeen million years ago, Earth's climates gradually heated up and then stayed warm for several million years. This event is termed the mid-Miocene Climatic Optimum (MMCO) and it was the last global warming event before the Ice Age. Still, what caused the warming and how it affected plants and animals remains unclear. This project uses plant fossils preserved in lake sediments in Washington, Idaho and Oregon to study how ecosystems changed during the MMCO. Specifically, the researchers will investigate whether CO2 (a greenhouse gas) emitted from Pacific Northwest (PNW) volcanoes during the mid-Miocene helped heat the atmosphere, how climate changed in the PNW, and how local plant communities adjusted to these changes. Mid-Miocene ecosystems were similar to today; therefore, learning about the MMCO helps predict what may happen to today's ecosystems experiencing climate change. Several graduate and undergraduate students are being trained, and a new display featuring MMCO research in the Burke Museum is being created. This project examines the causes and effects of mid-Miocene warming through the study of 18 exceptional PNW paleofloras from before, during and after the MMCO. Together, the floras form a sequence of linked data on atmospheric pCO2, regional climate change, and vegetation that can be precisely dated. The floras often preserve macrofossils, pollen, and phytoliths, providing an integrated view of local and regional climate and vegetation. Project aims are to: (1) do high-precision U-Pb geochronology on volcanic ashes at 13 floral sites across the MMCO; (2) study plant assemblages at all 18 sites to infer (a) vegetation composition, diversity, structure, and successional stage, (b) local-regional climate, and (c) atmospheric pCO2; and (3) use these data to evaluate the nature and timing of PNW ecosystem change during the MMCO. The project will contribute to a biogeographically more resolved understanding of how the Earth climate system and vegetation respond during global warming events.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.