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

1700万年前，地球的气候逐渐升温，然后保持温暖了几百万年。这一事件被称为中中新世气候适宜期（MMCO），是冰河时代之前最后一次全球变暖事件。然而，造成气候变暖的原因以及它如何影响植物和动物仍不清楚。该项目使用保存在华盛顿、爱达荷州和俄勒冈州湖泊沉积物中的植物化石来研究MMCO期间生态系统如何变化。具体来说，研究人员将调查中新世中期太平洋西北部（PNW）火山排放的二氧化碳（一种温室气体）是否有助于加热大气，PNW的气候如何变化，以及当地植物群落如何适应这些变化。中新世中期的生态系统与今天相似;因此，了解MMCO有助于预测今天经历气候变化的生态系统可能会发生什么。一些研究生和本科生正在接受培训，并在伯克博物馆创建了一个新的展示MMCO研究。该项目通过对MMCO之前、期间和之后的18个PNW古植物群的研究，探讨了中中新世变暖的原因和影响。这些植物群共同形成了一系列关于大气pCO 2、区域气候变化和植被的相关数据，这些数据可以精确地确定年代。植物区系通常保存有大型化石、花粉和植硅体，为当地和区域气候和植被提供了综合的视角。项目目标是：（1）对MMCO中13个植物区系的火山灰进行高精度U-Pb地质年代学研究;（2）研究所有18个植物区系的植物组合，以推断（a）植被组成、多样性、结构和演替阶段，（B）局部区域气候，（c）大气pCO 2;（3）利用这些数据评估MMCO期间PNW生态系统变化的性质和时间。该项目将有助于从地理学角度更好地理解地球气候系统和植被在全球变暖事件中的反应。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.