THE RELATIVE IMPORTANCE OF NORTHERN OVERFLOW AND SUBPOLAR DEEP CONVECTION FOR THE NORTH-ATLANTIC THERMOHALINE CIRCULATION

The relative importance of the formation of different North Atlantic D eep Water masses on the meridional overturning is examined with a non- eddy-resolving version of the CME model. In contrast to a frequently h eld belief, convective deep-water formation south of the North Atlanti c sill does not significantly force the large scale overturning if an adequate overflow across the sill can be represented by the model. The sensitivity of the meridional transport to the surface thermohaline f orcing is increased under alternate climatic conditions such as increa sed surface cooling or reduced overflow compared to the present-day si tuation. The results indicate that climate models may be too sensitive to decadal timescale variability of the surface forcing in subpolar r egions.