The Tropical Pacific Mean State, Annual Cycle and ENSO in Holocene Corals: a Multi-proxy Approach

厄尔尼诺-南方涛动（ENSO）是全球气候年际变化的主要模式，每隔几年就会影响全球的降水和温度模式。在气候变化的背景下，世界上越来越多的人容易受到自然灾害的影响，因此迫切需要更好地了解ENSO在未来可能发生的变化。虽然在过去十年中出现了有记录以来最大的三次厄尔尼诺现象，但尽管进行了广泛的研究，但关于ENSO在变暖的世界中将如何变化，仍存在很大的不确定性。观测是有限的，而最先进的气候模式也存在持续的误差。古气候重建扩展了短暂的观测记录，表明大约3000 - 5000年前的ENSO变异性大约是今天的一半，但这种减少的原因尚不清楚。ENSO与热带太平洋气候的长期状态密切相关，因此它的演变是理解这一时期地球历史的重要拼图。然而，这段时间热带太平洋背景状态的变化很少受到古气候记录的约束。该项目旨在重建赤道太平洋中心在过去5000年里从季节到千年的时间尺度上的温度和降雨演变。在此过程中，该项目将提供一种检验气候模型预测的方法。该项目将通过支持一名研究生和几名本科生开展独立的实验室研究项目，支持一名早期职业科学家首次担任首席项目负责人，以及支持两名积极从事科学教育、气候素养和向公众和政策制定者传播其研究成果的项目负责人，促进科学进步，推进科学教育，促进公众参与科学。更具体地说，该项目将利用Kiritimati化石珊瑚中d18O和微量元素的成对测量，定量地重建过去5000年来赤道太平洋中部海面温度和海水d18O的变化。微量元素测量将与大量收集的Kiritimati珊瑚d18O记录相结合，生成一套高度复制和定量的季节周期、ENSO极端事件和中赤道太平洋气候的长期演变重建。通过该项目，这些基于珊瑚的重建将与综合气候模型模拟进行比较，这些模型模拟受到地球进动周期变化的影响，利用正演模拟方法定量比较珊瑚数据与模型输出，并将在基里蒂玛蒂观测到的变化与热带太平洋及其他地区的变化联系起来。这些重建将对热带太平洋背景气候与ENSO之间的联系提供重要的见解，从而为预测未来的变化提供信息。在进行这些重建工作的同时，我们会制定珊瑚成岩作用评级工具，以促进在社会范围内评估和报告珊瑚化石成岩作用的标准。该奖项反映了美国国家科学基金会的法定使命，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。

The El Nino-Southern Oscillation (ENSO) is the dominant mode of year-to-year climate variability on a global scale, affecting precipitation and temperature patterns across the globe every few years. As a growing number of people around the world are vulnerable to natural disasters under a changing climate, there is an urgent need for improved understanding of how ENSO is likely to change in the future. While the last decade has seen three of the largest El Nino events on record, there is substantial uncertainty regarding how ENSO will change in a warmer world, despite extensive research efforts. Observations are limited, while state-of-the-art climate models suffer from persistent errors. Paleoclimate reconstructions, which extend the short observational record, suggest that ENSO variability around 3,000-5,000 years ago was about half as large as it is today, but the reason for this reduction is unknown. ENSO is closely tied to the long-term state of tropical Pacific climate, and thus its evolution represents an important piece of the puzzle in understanding this period of Earth history. However, changes in the tropical Pacific background state are poorly constrained from the paleoclimate record during this time. This project aims to reconstruct the evolution of temperature and rainfall from the center of the equatorial Pacific on timescales ranging from seasons to millennia over the past 5,000 years. In doing so, the project will provide a way to test predictions from climate models. The project will promote the progress of science, advance science education, and facilitate public engagement in the sciences by supporting a graduate student and several undergraduate students through independent laboratory-based research projects, by supporting an early career scientist in her first role as lead PI, and by supporting two PIs who are actively engaged in science education, climate literacy, and disseminating their research results to the general public and policymakers. More specifically, the project will quantitatively reconstruct central equatorial Pacific sea surface temperature and seawater d18O variability during the past 5,000 years using paired d18O and trace element measurements in Kiritimati fossil coral. Trace element measurements will be paired with an extensive collection of Kiritimati coral d18O records to generate a set of highly- replicated and quantitative reconstructions of the seasonal cycle, ENSO extremes and long-term evolution of central equatorial Pacific climate. Through the project, these coral-based reconstructions will be compared to comprehensive climate model simulations forced with changes in Earth's precessional cycle, utilizing a forward-modeling approach to quantitatively compare the coral data to model output and contextualize the changes observed at Kiritimati to changes across the tropical Pacific and beyond. These reconstructions will yield important insight into the linkages between the background tropical Pacific climate and ENSO that will inform projections of future change. In association with these reconstructions, a coral diagenesis rating tool will be developed to promote a community-wide standard for assessment and reporting of diagenesis in fossil corals.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.