NSFGEO-NERC: Collaborative Research: Role of the Overturning Circulation in Carbon Accumulation (ROCCA)

The North Atlantic Ocean plays an important role in the global carbon cycle, and it absorbs a disproportionately high amount of human carbon dioxide emissions. These points are thought to be closely related to the Atlantic Meridional Overturning Circulation (AMOC), but the balance of contributions to North Atlantic carbon accumulation from air-sea fluxes and ocean transports is not well constrained. There is significant uncertainty about what the future holds, both for AMOC strength and carbon uptake as they respond to the effects of climate change and other changing forcings. This project will utilize long-term and ongoing observations across the North Atlantic basin to quantify carbon uptake and carbon transport and the variability in these parameters on the time scale of decades. This work will support a variety of efforts to educate and promote underrepresented groups in ocean science. The project investigators will partner with a variety of institutions in Georgia, Florida and in the Caribbean to educate students at a range of levels. They will promote a carbon cycle education website that includes interactive K-12 education materials. This is a project jointly funded by the National Science Foundation’s Directorate for Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award recommendation, each Agency funds the proportion of the budget that supports scientists at institutions in their respective countries.The ROCCA project aims to redefine our understanding of the North Atlantic carbon system, one of the world’s most important regions for carbon sequestration on climatically-important timescales. The team will use new estimates of anthropogenic carbon transports across both subtropical and subpolar domains to determine the contributions of air-sea fluxes and ocean circulation to regional carbon accumulation, a fundamental knowledge gap. This analysis will enable evaluation of their combined effects on future carbon uptake as overturning strength is projected to weaken. New observations in Florida Straits will fully characterize the chemical variability in water mass structure on seasonal timescales for the first time, and in combination with air-sea anthropogenic CO2 fluxes derived from transport-divergence/accumulation budgets, the team will validate existing numerical simulations and improve the representation of carbon cycle processes in the next generation of climate models. The specific research objectives are to 1. Calculate anthropogenic carbon transports across the RAPID array at 26°N (2004 to 2024) and the subpolar OSNAP section (2014-2024), including sensitivity to AMOC changes; 2. Produce time-series of changing anthropogenic carbon inventory in the North Atlantic; 3. Air-sea anthropogenic carbon flux timeseries from accumulation (O1) and transport divergence (O2); 4. Constrain projections of future change and identify anthropogenic carbon transport / AMOC metrics; and 5. Assess the uncertainty of components of the observational approach, applying them to high-resolution model outputs.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.