The upper limb of the Atlantic Meridional Overturning Circulation (AMOC) brings shallow interocean contributions to replenish the North Atlantic export of deepwaters. It is primarily formed in the southern South Atlantic where the converging entrainment of Pacific and Indian Ocean waters meet and incorporate into the South Atlantic subtropical gyre (SASG) following a northward advection across the basin up to the western boundary. Here, the human-induced response of AMOC and SASG near-surface pathways are illustrated according to CESM1 Large Ensemble simulations from 1920 to 2100, where future projections derive from the most aggressive (yet most realistic) scenario in assumed fossil fuel use and greenhouse gas emissions. It is shown that the AMOC upper limb weakens not because less waters are being apported from the adjacent ocean basins — but because they are being mostly directed to recirculate in the anticlockwise SASG, turning back southward after reaching the South Atlantic western boundary.