A Numerical Study of the Influence of Tidal Mixing on Atlantic Meridional Overturning Circulation (AMOC) Simulation

The impact of the tidal mixing on the simulation of the Atlantic Meridional Overturning Circulation (AMOC) is an important issue in the ocean general circulation model. The response of AMOC to the tidal mixing is investigated in this study by comparing two experiments with and without tidal mixing using the LASG/IAP Climate System Ocean Model version 2 (LICOM2) that is coupled with the Community Ice Code version 4 (CICE4). The study is focused on impacts of tidal mixing on the change of AMOC intensity in the model. The simulation results show that the maximum strength of AMOC in the experiment with tidal mixing is closer to the value provided by RAPID (Rapid Climate Change Programme), which is almost double that in the control experiment without considering the tidal mixing. Meanwhile, the NADW cell reaches a depth of 3200 m, about 1000 m deeper than that in the control experiment, and is closer to that of the RAPID. The enhanced vertical diffusivity near the seafloor topography in the experiment with tidal mixing leads to a more unstable ocean stratification, which will enhance deep convection in the high latitudes of North Atlantic, especially in the Labrador Sea. This will strengthen AMOC intensity directly. Meanwhile, the upper ocean circulation is stronger in the experiment of tidal mixing, bringing more heat and salinity from the subtropics to the high latitudes and leading to denser surface water. The denser water subsequently destroys the stable stratification and intensifies the deep convection, resulting in stronger AMOC indirectly.