Southern Ocean influence on Atlantic Meridional Overturning Circulation across climate states

Various proxy data agree on a shallow Atlantic Meridional Overturning Circulation (AMOC) during the last glacial maximum (LGM), extending down to 2000 m - 2500 m depth, which is similar to the AMOC geometry projected by climate models over the 21^st century with rising atmospheric CO₂. The AMOC strength in the two climate states is insufficiently constrained. Here the Antarctic Bottom Water (AABW) and North Atlantic Deep Water (NADW) properties from proxy data and climate models are used to investigate their influences on the AMOC. It is primarily the AABW's potential density that determines the AMOC depth in both the LGM and warming climate. Changes in the potential density of the AABW, and the density contrast between NADW and AABW affect the pathways via which NADW returns to the surface and provide a constraint on AMOC strength. This study emphasizes the importance of the Southern Ocean in the AMOC's depth and strength across climate states.