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）是全球范围内每年气候变化的主要模式，每隔几年就会影响地球仪的降水和温度模式。由于全世界越来越多的人在不断变化的气候下易受自然灾害的影响，迫切需要更好地了解厄尔尼诺/南方涛动今后可能如何变化。虽然过去十年中发生了三次有记录以来最大的厄尔尼诺事件，但尽管进行了广泛的研究，但关于厄尔尼诺/南方涛动在一个更温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，而最先进的气候模型却不断出现错误。古气候重建扩展了短期观测记录，表明3000 - 5000年前的ENSO变化大约是今天的一半，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组成部分。然而，热带太平洋背景状态的变化在这段时间内受到古气候记录的限制。该项目旨在重建过去5,000年来赤道太平洋中心从季节到千年的时间尺度上的温度和降雨量的演变。在这样做的过程中，该项目将提供一种方法来测试气候模型的预测。该项目将促进科学的进步，推进科学教育，并通过支持一名研究生和几名本科生通过独立的实验室为基础的研究项目，通过支持早期职业科学家在她的第一个角色作为首席PI，并通过支持两名PI谁是积极从事科学教育，气候素养，并向公众和决策者传播其研究成果。更具体地说，该项目将利用Kiritimati珊瑚化石中的d18 O和微量元素成对测量值，定量重建过去5 000年中赤道太平洋中海面温度和海水d18 O的变化。微量元素测量将与广泛收集的Kiritimati珊瑚d18 O记录相结合，以生成一套高度复制和定量的季节周期，ENSO极端事件和赤道太平洋中部气候长期演变的重建。通过该项目，这些基于珊瑚的重建将与受地球岁差周期变化影响的综合气候模型模拟进行比较，利用前瞻性建模方法将珊瑚数据与模型输出进行定量比较，并将在Kiritimati观察到的变化与整个热带太平洋及其他地区的变化联系起来。这些重建将产生重要的洞察力的背景热带太平洋气候和厄尔尼诺/南方涛动之间的联系，将告知未来变化的预测。与这些重建相关联的是，将开发一个珊瑚成岩作用评级工具，以促进一个社区范围的标准，用于评估和报告化石珊瑚的成岩作用。该奖项反映了NSF的法定使命，并被认为值得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来支持。

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.