Collaborative Research: In Situ Investigations and Historical Analysis of Eddy Impacts on coastal carbon chemistry and coral calcification

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Mesoscale eddies, often referred to as the “weather” of the ocean, are energetic circulating currents in the ocean that can intensify upwelling of deeper waters or downwelling of surface waters. This in turn leads to changes in water chemistry and physical properties that can alter nutrient availability and rates of primary production, surface ocean pH, temperature, and salinity. Along the Gulf Stream in the mid-latitudes, eddy frequency is high with many transiting through the Sargasso Sea. While extensive research has been conducted on eddy physics and their impact on open-ocean biogeochemistry, there has been limited research on the impacts of eddies on coastal biogeochemistry, and, in particular, the effect of eddies on shallow warm-water coral reefs. Given the increasing stress coral reefs are facing due to anthropogenic changes, understanding how eddies may compound or relieve this stress is becoming increasingly important. In this project, three researchers from two institutions together with their undergraduate and graduate students will investigate the effect of mesoscale eddies on shallow water coral reefs in Bermuda, a coral reef surrounded island situated in the heart of the Sargasso Sea. Furthermore, the skills and knowledge gained from this proposal will be transferred through the STEM pipeline by a number of educational programs for high school students and teachers, and through undergraduate research opportunities at both institutions. The proposed research has three specific objectives that aim to improve current understanding of the role eddies play in reef biogeochemistry. (i) Does eddy activity affect water properties near shore, including temperature, nutrient availability, and carbon chemistry? (ii) How do the changes in water properties affect coral calcification? (iii) Can identified seawater changes be traced in coral skeleton archives to trace past eddy activity? This research will conduct sea water profiling along the rim reef study site to compare to similarly timed profiles at the Bermuda Atlantic Time-series Study (BATS) and Hydrostation S sites to understand how eddy driven changes propagate from offshore to onshore. In-situ water samplers and sensors will be deployed in Bermuda’s south shore rim reefs to study the impact of coastal eddies on the environmental conditions, and incubation chambers will be utilized to investigate how these conditions affect the primary process of reef formation, namely coral calcification. In addition, historical data from BATS and Hydrostation S occupations will be analyzed to identify years of high eddy activity to investigate changes to both the physical conditions and the carbon cycle at BATS in those years and compare them to recent records of coral paleo chemistry to identify eddy impacts in the proxy record for past reconstructions.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.