Previous studies have examined seasonal variations in the Atlantic Meridional Overturning Circulation (AMOC) at fixed latitudes, whereas its seasonal latitudinal co-variability and underlying mechanisms remain less understood. Using two data-assimilated products, this study investigates seasonal AMOC variations across subtropical latitudes by decomposing its upper limb transport into Ekman transport, driven directly by zonal wind stress, and non-Ekman transport, primarily arising from geostrophic flow. We find that seasonal variations in non-Ekman transport exhibit significant meridional coherence, which is linked to the geostrophic transport estimated from the pressure differences between the eastern and western boundaries. Sea surface height and density variations drive the pressure differences through barotropic and baroclinic adjustment, with stronger control from the eastern boundary. The contribution from ocean bottom pressure (sea surface height with steric height removed) represents a fast barotropic adjustment to seasonal pressure variations and explains about 75% of the variance in geostrophic transport. In contrast, the density-driven seasonal pressure variations propagate more slowly along the eastern boundary compared with the western boundary, indicating baroclinic adjustment. Seasonal pressure variations along the eastern boundary are influenced by both remotely propagated signals from the western boundary via wave adjustment and by local processes along the propagation pathway. Results from this study highlight the importance of examining the latitudinal connectivity of AMOC through analyses of its distinct dynamical components, and emphasize the role of fast-propagating waves in modulating seasonal variability in non-Ekman transport. Our study further suggests that understanding boundary processes, particularly ocean bottom pressure, may be a key aspect of investigating AMOC variability.

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