This study examines the importance of the Southern Ocean (SO) stratification in determining the upper cell of the Atlantic meridional overturning circulation (MOC) and stratification. Main results are based on a suite of idealized numerical simulations of the Atlantic with the prescribed density structure at the Atlantic southern boundary, intended to explore the importance of various factors. The results demonstrate that the density distribution at the SO-Atlantic boundary is the key factor controlling the Atlantic stratification and MOC, whereas the main importance of the Ekman and eddy (parameterized) exchanges is in setting the SO stratification. Among all aspects of the SO stratification, the position of the deep isopycnals near the western boundary of the Atlantic basin appears to determine the strength of the MOC for given isopycnal outcrop positions in the North Atlantic. The interplay between the SO stratification and surface density in the North Atlantic is, however, important for the MOC. In particular, the steady-state AMOC response to a negative North Atlantic density anomaly is shown to be amplified if the SO stratification is not allowed to change.
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