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.
