Collaborative Research: Central tropical Pacific climate variability over the last millennium

该奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。该项目将收集从赤道太平洋中部岛屿上恢复的古珊瑚的放射性碳年代片段，以研究过去1000年的气候条件。它将关注两个重要时期，中世纪气候异常期（850-1300年前）和小冰期（1400-1850年），以研究导致厄尔尼诺现象的因素。研究人员将以珊瑚骨骼中的生长带为目标，重建海水温度和盐度条件的月度分辨率记录。该项目为一些本科生和研究生提供研究、培训和教育机会。它还支持两名早期职业科学家和其他在参与K-16教育和公共宣传方面有良好记录的人之间的研究合作，重点是扩大多样性和包容代表性不足的社区。这些努力将继续下去，在附近一家少数民族服务机构举办客座讲座，并为当地高中生提供暑期研究机会。提高未来气候预估的准确性需要更全面地了解热带太平洋气候在广泛时间尺度上的内部和外部强迫变化。基于珊瑚的古气候记录极大地提高了我们对热带太平洋年际气候变化的理解，然而，由于(i)成岩作用，这可能严重影响珊瑚重建，以及（ii）珊瑚代理中的群落对群落的偏移，这在估计单个珊瑚的平均气候变化时引入了很大的不确定性，因此迄今为止，对百年尺度变化的类似见解仍然无法实现。根据在Kiritimati岛（2degN, 157degW） 20年的工作，该项目将生成约50个新的、年代准确的、多代理的过去千年气候变率记录。利用一种新颖的方法，将珊瑚氧同位素和Sr/Ca测量数据与一种新的古温度计Sr- u进行分层配对，该重建将提供第一套可靠的、定量的、独立的热带太平洋中部表面温度（SST）和水文气候趋势的估计，这些估计横跨中世纪气候异常（MCA; 900-1200CE）和小冰期（LIA; 1500-1800CE）。通过严格的成岩筛选和微尺度分析，从改变的珊瑚中提取可靠的气候信息，将进一步确保这些化石珊瑚记录的保真度。将这些新的重建与瞬态气候模拟进行比较，将为当前的趋势提供急需的背景，并使我们能够研究热带太平洋对外部强迫和气候反馈的长期反应。本项目的更广泛影响包括大大提高我们对热带太平洋自然气候变率的认识，使我们能够更好地量化区域人为气候趋势，并通过为气候模式提供更准确的基准来改进未来的气候预测。随着气候变化继续主导社会意识，PI将积极参与公众宣传工作，传播古气候研究成果以及有关未来气候变化对局部/区域影响的更一般信息。它支持对几名研究生的研究培训和指导，并为附近学区的高中生提供暑期研究体验，该学区有90%的少数民族学生未被充分代表。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。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). The project will assemble radiocarbon-dated segments of ancient coral recovered from islands in the central equatorial Pacific to study climate conditions during the last 1000 years. It will focus on two important time periods, the Medieval Climate Anomaly (850-1300 ago) and the Little Ice Age (1400-1850) to look at what factors cause El Nino conditions. Researchers will reconstruct monthly-resolution records of seawater temperature and salinity conditions by targeting growth bands in coral skeletons. This project supports research training educational opportunities for several undergraduate and graduate students. It also supports a research collaboration among two early career scientists and others who have a strong track record of participation in K-16 education and public outreach with an emphasis on broadening diversity and inclusion of underrepresented communities. These efforts will continue with guest lectures at a nearby minority-serving institution and by offering summer research opportunities for local high school students.Improving the accuracy of future climate projections requires a more complete understanding of internal vs. externally forced changes in tropical Pacific climate on a broad range of timescales. Coral-based paleoclimate records have dramatically improved our understanding of interannual climate variability in the tropical Pacific, however, similar insights into centennial-scale variability have thus far remained unattainable due to (i) diagenesis, which can significantly bias coral reconstructions, and (ii) colony-to- colony offsets in coral proxies, which introduce large uncertainties in estimates of mean climate change from single corals. Informed by two decades of work at Kiritimati Island (2degN, 157degW), this project will generate ~50 new well-dated and multi-proxy records of climate variability across the last millennium. Using a novel approach that layers paired coral oxygen isotope and Sr/Ca measurements, with a new paleothermometer, Sr-U, this reconstruction will provide the first set of robust, quantitative, and independent estimates of central tropical Pacific surface temperature (SST) and hydroclimate trends across the Medieval Climate Anomaly (MCA; 900-1200CE) and Little Ice Age (LIA; 1500-1800CE). The fidelity of these fossil coral records will be further ensured using rigorous screening for diagenesis and a microscale analyses to extract reliable climate information from altered corals. Comparisons of these new reconstructions with transient climate simulations will provide much-needed context for present-day trends and allow us to investigate the tropical Pacific’s long-term response to external forcings and climate feedbacks. Broader impacts to this project include a dramatic improvement to our understanding of natural climate variability in the tropical Pacific, allowing for the better quantification of regional anthropogenic climate trends, and the improvement of future climate projections by providing more accurate benchmarks for climate models. As climate change continues to dominate social consciousness, the PI will actively engage in public outreach efforts to communicate the results of the paleoclimate research as well as more general information about local/regional impacts of future climate change. It supports research training and mentoring of several graduate students and summer research experiences for high school students from a nearby school district which has a 90% underrepresented minority student population.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.