Pacific thermocline bridge revisited



The coupling on decadal time scales of the mid-latitude and tropical Pacific via an oceanic ‘bridge’ in the thermocline is investigated using ocean general circulation model hindcasts and a coupled ocean atmosphere model. Results indicate that in the tropics decadal anomalies of isopycnal depth are forced by Ekman pumping and are largely independent of the arrival of subducted anomalies in the thermocline that originate in the mid-latitudes of either hemisphere. In the coupled model, temperature anomalies on isopycnals show little coupling from the tropics to the northern hemisphere, but are lag correlated between southern hemisphere mid- and low-latitudes. However, anomaly magnitudes on the equator are small. These results suggest that the oceanic ‘bridge’ to the northern hemisphere explains only a small part of the observed decadal variance in the equatorial Pacific. Coupling to the southern mid-latitudes via temperature anomalies on isopycnals remains an intriguing possibility.