Resolving 20th Century Sea Surface Temperatures in the Central Equatorial Pacific with Laser Sr-U

太平洋中部海洋表面的变暖影响着全世界的天气模式。但我们目前对该地区过去的温度历史知之甚少，这影响了模式对未来天气的预测。这个项目使用100年前的热带珊瑚骨架来读取上个世纪的海洋温度。当海洋温度变化时，珊瑚骨骼的化学成分也会发生变化，这些信息被储存在生长带中，就像树木的年轮一样。激光被用来仔细取样珊瑚骨架，并在横跨太平洋的关键地点建立新的温度历史。有了这些新记录，科学家们可以评估像厄尔尼诺Niño这样的大规模天气事件的规模和频率，并改进用于预测未来天气状况的气候模型。该项目支持本科生的研究经验和培训，并为伍兹霍尔海洋研究所的博士后提供早期职业指导。赤道太平洋海温（sst）对地球气候系统有着巨大的影响，但在卫星时代开始之前，赤道太平洋海温的观测记录，特别是用于定义厄尔尼诺-南方涛动（ENSO）的尼诺3.4区域的观测记录很少。因此，在19世纪末和20世纪的大部分时间里，赤道太平洋海温的ENSO变率和长期趋势受到的约束很差，这对验证模式对未来气候的预估具有重要意义。本项目旨在利用基于珊瑚的Sr-U温度计重建赤道太平洋中部战略位置的代理海温的世纪长、连续、每月解析记录。本文开发并应用了一种新的激光消融方法，针对连续月度分离之间增加的骨骼，实现基于Sr-U的月度分辨率SST重建。从赤道太平洋西部、中部和东部收集的波利特珊瑚生成新的月分辨记录，以(1)在22℃至32℃的温度范围内校准月分辨Sr-U与观测到的月分辨海温；(2)将校准应用于在尼诺3.4和尼诺4.0区域的站点生成两个世纪的海温记录。这些站点的位置具有战略意义，可以捕捉20世纪CEP的海温趋势，20世纪ENSO事件的频率和幅度，以及这一时期中太平洋El Niño与东太平洋El Niño的相对频率。新的数据集将有助于解决有关赤道太平洋平均状态和变率对人为强迫的响应的悬而未决的问题。此外，该项目将开发新的方法，从现代和化石珊瑚中获得准确的海温月度记录，从而改变对热带太平洋气候的认识。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。

Warming of the surface ocean in the central Pacific affects weather patterns all over the world. But we currently know little about the past temperature history of this region which affects model projections of future weather. This project uses skeletons of 100-year old tropical corals to read ocean temperatures for the last century. The chemistry of coral skeletons changes when the ocean temperature changes and this information is stored in growth bands, much like rings in a tree. Lasers are used to carefully sample the coral skeleton and build new temperature histories at key locations across the Pacific Ocean. With these new records scientists can evaluate the size and frequency of large-scale weather events like El Niño and improve climate models used to predict future weather conditions. This project supports research experiences and training for undergraduate students as well as early career mentoring for a postdoctoral student at Woods Hole Oceanographic Institute.Sea surface temperatures (SSTs) of the equatorial Pacific exert an outsize influence on Earth’s climate system yet the observational record of equatorial Pacific SSTs, in particular the Nino 3.4 region that is used to define El Nino-Southern Oscillation (ENSO), is sparse prior to the start of the satellite era. Consequently, ENSO variability and the secular trend in equatorial Pacific SSTs are poorly constrained over much of the late 19th and 20th centuries with important implications for validating model projections of future climate. This project seeks to reconstruct century long, continuous, monthly resolved records of proxy SST from strategic locations in the central equatorial Pacific (CEP) using the coral-based Sr-U thermometer. A new laser ablation method is developed and applied, targeting skeleton accreted between successive monthly dissepiments, to enable Sr-U based SST reconstruction with monthly resolution. New monthly-resolved records from Porites coral collected in the western, central, and eastern equatorial Pacific will be generated to (1) calibrate monthly-resolved Sr-U versus observed monthly-resolved SST over a temperature range of 22 deg to 32 deg C and (2) apply the calibration to generate two century-long SST records at sites in the Nino 3.4 and Nino 4.0 regions. These sites are strategically located to capture the 20th century SST trend in the CEP, the frequency and amplitude of ENSO events over the 20th century, and the relative frequency of central versus east Pacific El Niño over this time period. The new datasets will help to resolve outstanding questions regarding the response of the equatorial Pacific mean state and variability to anthropogenic forcing. Additionally, the project will develop new methods for generating accurate monthly records of SST from modern and fossil corals and, in doing so, transform knowledge of the climate of the tropical Pacific.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.