Influence of a Weakened Atlantic Thermohaline Circulation on Tropical Pacific Climate Mean State and ENSO Variability

The responses of the global mean climate and the ENSO to a substantial weakening of the Atlantic Meridional Overturning Circulation(AMOC) are studied using water-hosing experiment in a coupled ocean-atmosphere general circulation model. With 1 Sv freshwater input in the North Atlantic, the AMOC slows down rapidly and weakens by almost 90%, reducing the northward oceanic heat transport, leading to a sea surface temperature(SST) dipole in the Atlantic. Through atmospheric teleconnections and local air-sea interaction, warm SST anomalies are found over the tropical Pacific. However, neither zonal SST gradient nor zonal wind stress changes significantly. The depth and slope of thermocline in tropical Pacific do not change too much, either. Accordingly, the variability of ENSO activity is essentially unchanged. These results indicate that in this model, fresh water perturbation may influence global mean climate, but has little impact on ENSO.