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

一千七百万年前，地球气候逐渐升温，然后在几百万年内保持温暖。这一事件被称为中中新世气候最佳(MMCO)，它是冰河世纪之前的最后一次全球变暖事件。尽管如此，是什么导致了气候变暖，以及它是如何影响动植物的，目前仍不清楚。该项目使用保存在华盛顿州、爱达荷州和俄勒冈州湖泊沉积物中的植物化石来研究MMCO期间生态系统是如何变化的。具体地说，研究人员将调查太平洋西北地区(PNW)火山在中新世中期排放的二氧化碳(一种温室气体)是否有助于加热大气，PNW地区的气候是如何变化的，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发生的情况。几名研究生和本科生正在接受培训，伯克博物馆正在制作一个以MMCO研究为特色的新展览。该项目通过对MMCO之前、期间和之后的18个异常的PNW古植物群的研究，研究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二氧化碳浓度、区域气候变化和植被的关联数据，可以精确地确定日期。植物群通常保存着大型化石、花粉和植物硅体，提供了当地和地区气候和植被的综合景观。该项目的目标是：(1)对MMCO的13个花卉地点的火山灰进行高精度的U-Pb年代学；(2)研究所有18个地点的植物组合，以推断(A)植被组成、多样性、结构和演替阶段；(B)当地区域气候；(C)大气二氧化碳；(3)使用这些数据来评估在MMCO期间PNW生态系统变化的性质和时间。该项目将有助于对地球气候系统和植被如何在全球变暖事件中做出反应的生物地理更清晰的理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.