The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the Earth’s climate system, yet the mechanisms of its multidecadal variability/changes remain under active debate. In particular, the role of open-ocean deep convection versus the role of Arctic, which supplies the densest waters that feed the AMOC, has been widely discussed. Here, we present results from two modeling studies investigating the mechanisms of multidecadal AMOC variability/changes, with a particular emphasis on the important linkage between the AMOC and the Arctic Ocean.
Using an ensemble of water hosing experiments, we examine mechanisms of multidecadal AMOC weakening. We find that the multidecadal AMOC decline is associated with subsurface cooling and freshening in the subpolar North Atlantic and the decline in the deep ocean west–east density contrast across the subpolar basin. The Labrador Sea open-ocean deep convection, which strengthens rather than weakens, is not a cause of the multidecadal AMOC decline. 
To further investigate the upstream influence of the Arctic, we constrained the eastern Arctic Ocean in a coupled model using the observed hydrographic climatology. Our results demonstrate that a colder and saltier Arctic Eurasian Basin could densify the Arctic outflow, shift the southward AMOC branch across Arctic-Atlantic gateway sections and across the eastern subpolar North Atlantic toward denser levels. The results show that the modeled multidecadal AMOC changes in response to changes in the eastern Arctic Eurasian Basin are not dominated by changes in open-ocean deep convection in either the Greenland or Labrador Seas. 
These results support the view that the Arctic Ocean is the northern terminus of the AMOC, supplying the densest waters feeding the AMOC. These findings highlight the need to accurately represent the Arctic Eurasian Basin water mass properties in coupled climate models to simulate a realistic dense AMOC outflow and associated multidecadal AMOC variability/changes.