EAR-PF: Mid-Miocene climate, vegetation, and disturbance dynamics of the Pacific Northwest

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Dr. Christopher Schiller has been awarded an NSF EAR Postdoctoral Fellowship to conduct research, professional development, and outreach activities at the University of Washington and Boise State University under the mentorship of Drs. Caroline Stromberg and Mark D. Schmitz, respectively. Understanding the Earth system under climates warmer than today is a useful approach for understanding the consequences of future warming resulting from human-caused climate change. One such warm period in the Earth’s history is the Mid-Miocene Climatic Optimum (MMCO), approximately 17-14 million years ago, when global temperatures were 4-7°C warmer than the modern, pre-industrial period. Fossil plant assemblages from the MMCO have been used to understand how the climate and ecosystems of that time functioned on long (millions of years) timescales. However, the importance of climate and ecosystem processes that function on shorter (hundreds of thousands of years and shorter) timescales has not often been considered. New research has suggested that climate change on short timescales and large, frequent volcanic eruptions may have greatly affected MMCO ecosystems. Therefore, it becomes unclear if ecosystem changes seen in fossil plant assemblages are representative of long-term climate conditions or a response to short-term processes. This study of MMCO vegetation in the Pacific Northwest aims to understand the cause of ecosystem change seen in fossil plants. Fossil pollen assemblages will be studied to examine ecosystem change over short timescales and if climate, fire, or volcanic eruptions may have caused those changes. Specifically, this project will examine two mid-Miocene paleofloras in Oregon, the Succor Creek Flora and Mascall Flora, from which short-term (high-resolution) vegetation states will be reconstructed from pollen and contemporaneous ecological disturbances of several types will be constructed from charcoal (fire), polycyclic aromatic hydrocarbons (fire), elemental geochemistry (landscape stability), and detailed lithological descriptions (landscape stability and volcanic eruptions). Short-term records will be compared with long-term (coarse-resolution) vegetation records, which will be produced from longer stratigraphic sections from the same floras and Miocene-length records produced from a concurrent project (EAR-1924390). Suites of U-Pb zircon dates from each flora will allow for a robust chronology for all vegetation-disturbance reconstructions and enable correlation with insolation solutions and marine climate records. This project will contribute a modern examination of the understudied field of pre-Quaternary palynology, an investigation of the response of vegetation to a past period of dramatic climate change and intense volcanism, and an application of multiple proxies to understand MMCO ecosystem function, and mentorship of undergraduate science students.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.