Contrasting Response of the Eastern and Western North Atlantic Circulation to an Episodic Climate Event*

Abstract

Abstract Regional observational studies in the North Atlantic have noted significant hydrographical shifts in 1997–98 because of the episodic drop in the North Atlantic oscillation (NAO) during 1996. Investigation using a basin-scale model finds that, although the western North Atlantic (WNA) witnessed unusually low-salinity water by 1997, the eastern North Atlantic (ENA) simultaneously evidenced intrusions of high-salinity water at intermediate depths. This study shows that a major source of high salinity in the ENA is from the northward penetration of Mediterranean Outflow Water (MOW) that occurred concurrently with a westward shift of the subpolar front. The authors confirm that the low-salinity intrusion in the WNA is from enhanced Labrador Current flow. Results from climatological high- and low-NAO simulations suggest that the NAO-induced circulation changes that occurred in 1997–98 are a characteristic North Atlantic basin response to different forcing conditions during characteristic high- and low-NAO periods.