Collaborative Research: Multi-century hydrologic and NAO variability in the tropical Western Atlantic - A Marine NAO Synthesis

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Understanding climate variability in the North Atlantic region is critical to society in the Eastern United States, Western Europe and beyond. In particular, the North Atlantic Oscillation (NAO), an atmospheric pressure system that alters sea surface temperatures, influences land temperature, drought, and storm tracks across the dense population centers of the US and Europe. While we can now measure the NAO each year, little is known about its longer-term behavior, or how its behavior may change in the future. This project will generate records of past climate change using corals from the island of Tobago in the southern Caribbean Sea, a region especially sensitive to the effects of the NAO. Drill cores of giant brain corals will be taken using SCUBA, and chemical analysis of the cores will be used to generate monthly histories of temperature, salinity and rainfall that extend back over the past several centuries. These climate records will provide insights into the temporal and spatial patterns of tropical Atlantic climate variability, particularly the large-scale processes associated with the NAO. This international collaboration will support a graduate student from The University of Trinidad and Tobago to travel to AMNH and WHOI for mentorship and training in coral x-ray and geochemical analysis. The project also includes active participation in the educational and outreach programs at both AMNH and WHOI, including the Hall of Planet Earth, among the top five halls chosen by AMNH visitors and school groups.This project will contribute directly to NSF's Paleo Perspectives on Climate Change (P2C2) goals by generating high resolution (monthly), multi-century long records of the hydrologic properties in the southern Caribbean Sea, including sea surface temperature (SST), sea surface salinity (SSS) and local river runoff. The study will result in collection of two multi-century coral drill cores from northeastern Tobago, and subsequently the construction of paleoclimate records that resolve the full seasonal cycle, critical for identifying signatures of regional forcing such as the North Atlantic Oscillation (NAO). Strontium-calcium (Sr/Ca) ratios will be used to reconstruct SST, and oxygen isotope (del18O) ratios together with Sr/Ca will be used to reconstruct SSS. Finally, barium-calcium (Ba/Ca) ratios will yield records of terrestrial input and river runoff. This investigation will target Siderastrea and Colpophyllia coral species previously shown to faithfully record climatic variables with skeletal geochemical proxies. A winter-season SST reconstruction from this sensitive site will capture long-term NAO variability, and comparison with existing records of the NAO and SST from the Atlantic and Red Sea will allow investigation of regional coherence and changes in the spatial stationarity of the marine NAO signal over the past few centuries.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.