AMOC stability and diverging response to arctic sea ice decline in two climate models

This study compares the impacts ofArctic sea ice decline on theAtlanticmeridional overturning circulation (AMOC) in two configurations of the Community Earth SystemModel with different horizontal resolution. In a suite ofmodel experiments, we impose radiative imbalance at the ice surface, replicating a loss of sea ice cover comparable to that observed during 1979-2014, and we find dramatic differences in theAMOCresponse between the twomodels. In the lower-resolution configuration, theAMOCweakens by about one-third over the first 100 years, approaching a new quasi-equilibrium. By contrast, in the higher-resolution configuration, the AMOC weakens by;10% during the first 20-30 years followed by a full recovery driven by invigorated deep water formation in the Labrador Sea and adjacent regions.We investigate these differences using a diagnosticAMOCstability indicator,which reflects the AMOC freshwater transport in and out of the basin and hence the strength of the basin-scale salt-advection feedback. This indicator suggests that theAMOCin the lower-resolution model is less stable and more sensitive to surface perturbations, as confirmed by hosing experiments mimicking Arctic freshening due to sea ice decline. Differences between the models' mean states, including the Atlantic Ocean mean surface freshwater fluxes, control the differences in AMOC stability. Our results demonstrate that the AMOC stability indicator is indeed useful for evaluatingAMOCsensitivity to perturbations.We emphasize that, despite the differences in the long-term adjustment, both models simulate a multidecadal AMOC weakening caused by Arctic sea ice decline, relevant to climate change.