The Role of Wind and Buoyancy in a Turbulence-Resolving Model of the Atlantic Meridional Overturning Circulation

Abstract

The Atlantic meridional overturning circulation (AMOC) in the North Atlantic Ocean is shaped by mechanical and buoyancy forcing, with critical components like the Gulf Stream, gyres, dense water formation, and deep water upwelling. The AMOC is undergoing significant variability due to changes in forcing from the rapidly changing climate. However, limited understanding and resolution in capturing deep convection and boundary layer dynamics lead to inaccuracies in future ocean mass and heat transport estimations. This study employs novel turbulence- and convection-resolving simulations of an idealized, laboratory-scale North Atlantic Ocean model to investigate these effects. The simulation captures key features observed in the North Atlantic Ocean, including the AMOC, downwelling and upwelling, boundary currents, thermocline layers, gyres, fronts, and baroclinic eddies. With the presence of wind, two distinct thermocline layers form in the subtropics due to Ekman pumping: the “ventilated thermocline” near the surface and the “internal thermocline” below. We examine two scaling theories to quantify meridional and gyre transport based on these thermocline layers. Our findings indicate that meridional transport increases with both buoyancy and wind forcing, while zonal transport is enhanced by wind and shows some dependence on buoyancy forcing. We find that upwelling near the western boundary intensifies with increased wind and buoyancy forcing, while downwelling from convection occurs along the northeastern boundary and from Ekman pumping in the subtropics, highlighting the three-dimensional structure of the AMOC. Our results demonstrate the interconnectedness of gyres and deep overturning circulation, offering insights toward refining turbulence and convection parameterizations in ocean models.