q Springer-Verlag 1996 On the freshwater forcing and transport of the Atlantic thermohaline circulation

Abstract. The ‘conveyor belt ’ circulation of the Atlan-tic Ocean transports large amounts of heat northward, acting as a heating system for the northern North At-lantic region. It is widely thought that this circulation is driven by atmospheric freshwater export from the At-lantic catchment region, and that it transports fresh-water northward to balance the loss to the atmosphere. Using results from a simple conceptual model and a global circulation model, it is argued here that the freshwater loss to the atmosphere arises mainly in the subtropical South Atlantic and is balanced by north-ward freshwater transport in the wind-driven subtropi-cal gyre, while the thermohaline circulation transports freshwater southward. It is further argued that the di-rection of freshwater transport is closely linked to the dynamical regime and stability of the ‘conveyor belt’: if its freshwater transport is indeed southward, then its flow is purely thermally driven and inhibited by the freshwater forcing. In this case the circulation is not far from Stommel’s saddle-node bifurcation, and a circula-tion state without NADW formation would also be sta-ble.