The Atlantic Meridional Overturning Circulation (AMOC) is a fundamental component of the global climate system, with most of its net sinking occurring along the boundaries of the Subpolar Gyre (SPG) in the North Atlantic. Previous observational and model studies have highlighted that the role of both barotropic and baroclinic transports in the boundary currents in governing vertical transport in the marginal seas of SPG. In this study, using two high-resolution numerical results from 1980 to 2019, we investigate the interannual to decadal variability of downwelling within the SPG, identifying boundary downwelling in the eastern SPG—specifically in the Irminger Sea and Iceland Basin—as a critical driver of AMOC downwelling variability. This variation in boundary downwelling is primarily controlled by baroclinic transport, driven by along-shore temperature gradients. Changes in the strength of the North Atlantic Current and associated meridional heat transport in the intergyre region regulate the influx of subtropical heat into the eastern SPG, altering the along-shore temperature gradients and, consequently, the boundary downwelling. On interannual to decadal timescales, we conclude that the eastern SPG is a key driver of AMOC downwelling, with boundary temperature changes playing a pivotal role. This study emphasizes the crucial influence of boundary processes in shaping AMOC variability and highlights their significant implications for climate dynamics.

overturning circulation, downwelling, North Atlantic Ocean