Global teleconnections in response to a shutdown of the Atlantic meridional overturning circulation

Abstract

The global response to a shutdown of the Atlantic meridional overturning circulation (AMOC) is investigated by conducting a water-hosing experiment with a coupled ocean-atmosphere general circulation model. In the model, the addition of freshwater in the subpolar North Atlantic shuts off the AMOC. The intense cooling in the extratropical North Atlantic induces a widespread response over the global ocean. In the tropical Atlantic, a sea surface temperature (SST) dipole forms, with cooling north and warming on and south of the equator. This tropical dipole is most pronounced in June-December, displacing the Atlantic intertropical convergence zone southward. In the tropical Pacific, a SST dipole forms in boreal spring in response to the intensified northeast trades across Central America and triggering the development of an El Niño-like warming that peaks on the equator in boreal fall. In the extratropical. North Pacific, a basinwide cooling of ∼°C takes place, with a general westward increase in intensity. A series of sensitivity experiments are carried out to shed fight on the ocean-atmospheric processes for these global teleconnections. The results demonstrate the following: ocean dynamical adjustments are responsible for the formation of the tropical Atlantic dipole; air-sea interaction over the tropical Atlantic is key to the tropical Pacific response; extratropical teleconnection from the North Atlantic is most important for the North Pacific cooling, with the influence from the tropics being secondary; and the subtropical North Pacific cooling propagates southwestward from off Baja California to the western and central equatorial Pacific through the wind-evaporation-SST feedback. © 2008 American Meteorological Society.