Collaborative Research: Fossil Coral Records of ENSO and Tropical Pacific Climate Through the Late Holocene

在预测未来气候变化的过程中，最紧迫的问题之一是气候的变化是否取决于气候系统的平均状态。这个问题的很大一部分涉及厄尔尼诺/南方涛动现象的行为：例如，随着气候变暖，厄尔尼诺现象是否变得更强、更频繁？这个项目将通过编制过去6000年的ENSO和热带太平洋气候的记录来解决这个问题。过去6000年的特点是太阳辐射季节性的已知变化。这些重建将测试ENSO系统是否受到这些太阳辐射变化的影响，如果是，变化是如何以及何时发生的。为了重建ENSO行为，在热带太平洋中部的几个Line群岛（Palmyra， Fanning和Christmas Islands）的海滩上收集的~12个化石珊瑚的骨骼组成将使用U/Th技术进行年代测定，并以月分辨率分析其稳定同位素和元素组成。先前的研究表明，该地区现代珊瑚的骨骼化学捕获了ENSO的月度分辨率记录，其保真度与仪器观测相当。初步数据表明，化石珊瑚的地球化学没有改变，与现代珊瑚相当，化石珊瑚样本的年龄具有小于6000年的连续年龄的特点。这项研究的广泛影响将对寻求提高对气候变率的理解和预测的气候建模者具有不可估量的价值，该项目将支持研究生和本科生的培训。这项研究还具有与气候变化和全球变暖等更广泛的问题相关的社会政治影响。

One of the most pressing questions in the projection of future climate change is the issue of whether the variability of climate depends on the average state of the climate system. A large part of this question involves the behavior of the El Nino/Southern Oscillation phenomenon: for example, do El Nino events become stronger and more frequent as the climate warms? This project will address this question by developing a record of ENSO and tropical Pacific climate that spans the last 6,000 years - a period characterized by known changes in the seasonality of solar radiation. These reconstructions will test whether the ENSO system was forced by these solar radiation changes and if so, how and when changes occurred. To reconstruct ENSO behavior, the skeletal composition of ~12 fossil corals that were collected on the beaches of several of the Line Islands in the central tropical Pacific (Palmyra, Fanning and Christmas Islands) will be dated using U/Th techniques and analyzed with monthly resolution for their stable isotope and elemental composition. Previous research has shown that the skeletal chemistry of modern corals in this region captures a monthly-resolved record of ENSO with a fidelity that is on par with instrumental observations. Preliminary data suggest that the fossil coral geochemistry has not been altered, it is comparable to modern corals, and the ages of the fossil coral samples are characterized by a continuum of ages less than 6,000 years old. The broader impacts of this research will be invaluable to climate modelers seeking to improve the understanding and prediction of climate variability and the project will support graduate and undergraduate student training. This study also has socio-political impact that is related to the broader issues of climate change and global warming.