GYRE-induced variability in North Atlantic circulation - Dynamics and impacts on overturning

The large-scale circulation in the North Atlantic Ocean plays a key role in regulating climate by transporting warm, salty waters northward along the borders of the subtropical gyre and the subpolar gyre within the extended Gulf Stream system. The role of variable gyre circulation in modulating the northward transport between the gyres and thus influencing the large-scale Atlantic Meridional Overturning Circulation (AMOC) does, however, remain unexplored. GYRED will quantify variability in the transport between the gyres versus recirculation within the gyres, identify the forcing mechanisms of variable northward transport, and assess the impact on the AMOC and on poleward ocean heat transport. Determining the effect of gyre-induced variability on the large-scale ocean circulation will impact the interpretation of observational estimates of circulation strength at various measurement sites in the North Atlantic and Nordic Seas. The project will thus pave the way for early detection and improved predictions of future changes in the extended Gulf Stream system and the AMOC.

The Gulf Stream and the Atlantic Meridional Overturning Circulation (AMOC) are expected to weaken during the 21st century under continued global warming, with potential far-reaching consequences for poleward ocean heat transport, coastal sea level, and storage of carbon and oxygen in the deep-ocean. A main challenge in predicting and detecting potential trends in the large-scale North Atlantic circulation is the apparent lack of coherent change between the subtropical North Atlantic, subpolar North Atlantic, and Nordic Seas on interannual to decadal time scales. GYRED will determine the role of variable recirculation within, and throughput between, the gyres in limiting basin-wide coherence by systematically quantifying variable throughput between the gyres, identifying the forcing mechanisms of variable throughput, and isolating the response in the AMOC and poleward ocean heat transport. Finally, GYRED will investigate future changes in the North Atlantic gyre circulation under different emission scenarios and assess the associated impacts on the AMOC. Determining the role of gyre-induced variability in the large-scale circulation will have major implications for the interpretation of the observational record at various measurement sites in the North Atlantic and Nordic Seas. The project will thus pave the way for early detection and improved predictions of future changes in the extended Gulf Stream system and the AMOC, important for assessing safe operating spaces around a major climate tipping point.