Award: OCE-1747746

Earths climate varies naturally on decadal through millennial timescales. Superimposed upon, and interacting with, these natural variations is the human footprint on climate caused by anthropogenic emissions of greenhouses gases to the atmosphere. One critical goal of the scientific community is to resolve the anthropogenic influence from the natural variability, and thus improve our understanding of humanities impact and better predict future climate. Accurate, continuous records that allow us to constrain the frequency and magnitude of natural variability on decadal through millennial timescales, are sorely needed to achieve this goal. The ocean is the Earths thermometer and records of past ocean temperature contribute significantly to our understanding of low frequency climate change. The skeletons of long-lived corals contain records of past ocean temperature that we cannot get from any other source. However reading the coral record is not straightforward because non-climate factors, such as the type of coral, its growth rate and even its health, can influence the way it archives this information. To overcome these issues, we developed a new thermometer called Sr-U that is based on a robust understanding of the processes by which corals build skeletons and archive the oceanographic information. Under this award, we developed a new temporal Sr-U SST calibration using geochemical data generated from three modern Atlantic corals of two different genera (Orbicella and Siderastrea). The correlation between Sr-U and SST is very strong (r2=0.74, p<0.001) and we applied the calibration to Sr-U data generated from a fourth coral, a Siderastrea spp. from the island of Martinique in the Lesser Antilles. The 46-year long Sr-U SST record from the Martinique coral captured the mean SST, inter-annual variability and the warming trend evident in the satellite-based SST record. We also applied the new calibration to a 100-year long Sr-U record from a Puerto Rico coral. The new Sr-U SST record captured absolute SSTs, SST variability and the 20th century warming trend at Puerto Rico evident in the instrumental record. Under this award we successfully demonstrated the ability of the Sr-U thermometer to return accurate records of SST, and significantly improve upon Sr/Ca-derived estimates. One peer-reviewed manuscript and one Masters thesis (University of Puerto Rico) was produced under this award. Three presentations were given at international conferences and one WHOI Summer Student Fellow project was completed. One graduate and one undergraduate student successfully completed projects under this award and presented their work at international conferences. Last Modified: 04/28/2019 Submitted by: Anne Cohen