Dominance of North Atlantic Ocean processes on the AMOC multicentennial variability

In our previous study, we found that the multicentennial variability (MCV) of the Atlantic Meridional Overturning Circulation (AMOC) in a CESM1 pre-industrial control simulation is primarily influenced by processes in the North Atlantic, especially the anomalous advection of mean salinity and the mean advection of salinity anomaly. In this study, we extend this finding to the IPSL-CM6A-LR and EC-Earth3-LR model simulations, revealing that the role of North Atlantic-originated processes in AMOC MCV is consistent across these models. Specifically, the anomalous advection of mean salinity and the mean advection of salinity anomaly remain key drivers of AMOC MCV in both models. Previous research has focused on the mean advection of salinity anomalies driven by Arctic sea-ice in the IPSL-CM6A-LR and EC-Earth3-LR models, leading to the partial conclusion that the Arctic Ocean dominates AMOC MCV. However, processes originating from the Arctic Ocean also include changes in the surface freshwater flux in the subpolar deep-water formation region. As Arctic sea ice melts, it reduces the amount of sea ice available to melt in the subpolar region. These two Arctic Ocean processes—one weakening and the other enhancing the AMOC anomaly—largely balance each other out, so the net effect of the Arctic Ocean on AMOC MCV is nearly neutral. Therefore, we conclude that the primary driver of AMOC MCV is processes originating from the North Atlantic, not the Arctic Ocean.