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

该奖项全部或部分根据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发现的经放射性碳定年的古珊瑚片段，以研究过去1000年的气候条件。 它将集中在两个重要的时间段，中世纪气候异常（850-1300年前）和小冰期（1400-1850年），看看是什么因素导致厄尔尼诺现象的条件。 研究人员将通过瞄准珊瑚骨骼中的生长带来重建海水温度和盐度条件的月度分辨率记录。 该项目支持研究培训教育的机会，为一些本科生和研究生。 它还支持两名早期职业科学家和其他在K-16教育和公共宣传方面有着良好记录的人之间的研究合作，重点是扩大代表性不足的社区的多样性和包容性。 这些努力将继续在附近的少数民族服务机构客座讲座，并通过提供夏季研究机会，为当地高中生。提高未来气候预测的准确性，需要更全面地了解内部与外部强迫变化的热带太平洋气候在广泛的时间尺度。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，这可能会显着影响珊瑚重建，以及（ii）珊瑚代理中的殖民地与殖民地偏移，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，因此到目前为止，对百年尺度变化的类似见解仍然无法实现。根据在基里蒂马蒂岛（2degN，157 degW）20年的工作，该项目将在过去的一千年中产生约50个新的日期明确的多代理气候变化记录。使用一种新的方法，层配对珊瑚氧同位素和Sr/Ca测量，与一个新的古温度计，Sr-U，这种重建将提供第一套强大的，定量的，独立的估计中热带太平洋表面温度（SST）和水文气候趋势的中世纪气候异常（MCA; 900- 1200 CE）和小冰期（LIA; 1500- 1800 CE）。将通过严格筛选成岩作用和微型分析，从改变的珊瑚中提取可靠的气候信息，进一步确保这些珊瑚化石记录的准确性。这些新的重建与瞬态气候模拟的比较，将提供急需的背景下，目前的趋势，使我们能够调查热带太平洋的长期响应外部强迫和气候反馈。 对该项目的更广泛影响包括极大地提高了我们对热带太平洋自然气候变率的理解，从而可以更好地量化区域人为气候趋势，并通过为气候模型提供更准确的基准来改进未来气候预测。随着气候变化继续主导社会意识，PI将积极参与公共宣传工作，以传达古气候研究的结果以及有关未来气候变化对当地/区域影响的更多一般信息。 它支持研究培训和指导几个研究生和暑期研究经验的高中学生从附近的学区，有90%的少数民族学生人数不足。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

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.