Diapycnal Mixing in Transient Responses of the Atlantic Meridional Overturning Circulation in an Enhanced Freshwater Perturbation Experiment

It has been reported recently that the simulated Atlantic meridional overturning circulation (AMOC) using the coupled Bergen climate model (BCM) showed initial intensity declines followed by gradual recoveries over a 150-year enhanced freshwater input experiment. Stratification-dependent oceanic diapycnal mixing has been hypothesized as a reason for the simulated recovery of the AMOC. This study investigated the role of diapycnal mixing in transient responses of simulated AMOCs. Our results showed that stratification-dependent diapycnal mixing can cause stronger upwelling of deep water in the tropical Atlantic than that produced under conditions of fixed diapycnal mixing. Moreover, simulated AMOCs were more sensitive to active stratification-dependent diapycnal mixing than fixed mixing. However, stratification-dependent diapycnal mixing cannot be conclusively singled out as the critical cause of the recoveries of simulated AMOCs under enhanced-freshwater inputs.