Suppressed AMOC multidecadal variability by freshwater flux change in the Community Earth System Model version 1.0

Abstract

The multidecadal variability of Atlantic Meridional Overturning Circulation (AMOC) significantly impacts various climate phenomena, yet the role of ocean surface freshwater flux in this variability is not fully understood. Through experiments with and without surface freshwater flux adjustment under pre-industrial conditions based on the Community Earth System Model version 1.0, we demonstrate that active freshwater flux variability, particularly sea ice melt, can suppress the amplitude and period of the AMOC multidecadal variability by influencing sea surface salinity and density. Specifically, active freshwater flux rapidly shifts density anomalies between the AMOC positive and negative phases. When the AMOC is in its positive phase, the previously weaker state can induce negative surface temperatures in the deep water formation region. This temperature anomaly raises sea level pressure and introduces westerly anomalies over the subpolar North Atlantic, promoting sea ice expansion and increasing sea ice melt. The increased sea ice melt reduces surface salinity, driving the AMOC into its negative phase. This process is also responsible for suppressing the amplitude of the AMOC variability. The opposite process occurs when the AMOC is in its negative phase. Our findings highlight the critical role of freshwater flux in affecting the AMOC multidecadal variability in both current and changing climates.