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This study identifies key features associated with the Atlantic multidecadal variability (AMV) in both observations and a fully coupled climate model, e.g., decadal persistence of monthly mean subpolar North Atlantic (NA) sea surface temperature (SST) and salinity (SSS) anomalies, and high coherence at low frequency among subpolar NA SST/SSS, upper ocean heat/salt content, and the Atlantic Meridional Overturning Circulation (AMOC) fingerprint. These key AMV features, which can be used to distinguish the AMV mechanism, cannot be explained by the slab ocean model results or the red noise process but are consistent with the ocean dynamics mechanism. This study also shows that at low frequency, the correlation and regression between net surface heat flux and SST anomalies are key indicators of the relative roles of oceanic versus atmospheric forcing in SST anomalies. The oceanic forcing plays a dominant role in the subpolar NA SST anomalies associated with the AMV.

Plain Language Summary The low frequency variability in the North Atlantic ocean temperature has been shown to exhibit various important climate impacts at global and regional scales. Understanding the physical mechanism for the low frequency variability in the North Atlantic ocean temperature is crucial for successful future predictions in the North Atlantic ocean temperature and associated climate impacts. This study identifies key features associated with the Atlantic Multidecadal Variability in both observations and a fully coupled climate model: e.g., decadal persistence of subpolar North Atlantic sea surface temperature and salinity anomalies, and the high coherence among them and the Atlantic Meridional Overturning Circulation fingerprint at low frequency. These key features, which can be used to distinguish the mechanisms for the Atlantic Multidecadal Variability, cannot be explained as a response forced by the atmospheric white noise, but are consistent with the ocean dynamics mechanism. This study also shows that at low frequency, the correlation and regression between net surface heat flux and sea surface temperature anomalies are key indicators of the relative roles of oceanic versus atmospheric forcing in temperature anomalies. The oceanic forcing plays a dominant role in the low frequency subpolar North Atlantic sea surface temperature anomalies associated with the Atlantic Multidecadal Variability.