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Abstract

It has been hypothesized that climate variability on centennial timescales is linked to internal variability of the Meridional Overturning Circulation in the North Atlantic, although mechanisms linking Atlantic MOC variability to other ocean basins have also been proposed. These mechanisms of centennial-scale variability have typically been derived in single-model studies using long control integrations of a coupled climate model, but so far no robust picture of centennial-scale MOC variability has emerged. Here, we analyze centennial-scale AMOC variability and its connections to other ocean basins in the multi-model ensemble of CMIP6 piControl simulations. Numerous CMIP6 models exhibit a significant mode of centennial-scale AMOC variability with a discernible imprint on surface temperatures. We identify a consistent pattern of salinity exchanges between the Arctic and North Atlantic basins in models which include the NEMO ocean component, although it appears that only few aspects of this mechanism can be generalized to the full CMIP6 ensemble. Further, we find that internal variations in AMOC strength covary with convection in both the Labrador Sea and the Nordic Seas in models that include NEMO, and discuss the importance of intermittent sea ice cover in the convective regions for amplifying this centennial-scale AMOC variability.