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

未来气候变化预测中最紧迫的问题之一是气候的可变性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，厄尔尼诺事件是否随着气候变暖而变得更加强烈和频繁？该项目将通过建立跨越过去6000年的ENSO和热带太平洋气候的记录来解决这个问题--这段时期的特点是太阳辐射的季节性发生了已知的变化。这些重建将测试ENSO系统是否被这些太阳辐射变化所强迫，如果是的话，变化是如何发生的以及何时发生的。为了重建ENSO行为，将使用U/Th技术测定热带太平洋中部莱恩群岛(巴尔米拉、范宁和圣诞岛)海滩上采集的12个珊瑚化石的骨骼组成，并对其稳定同位素和元素组成进行月分辨率分析。以前的研究表明，该地区现代珊瑚的骨骼化学捕捉到了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，化石珊瑚样品的年龄具有不到6000年的连续年龄特征。这项研究的更广泛影响将对寻求改善对气候变异性的理解和预测的气候模型师来说是无价的，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.