A coarse resolution model is developed to study the thermohaline circulation of the North Atlantic. This model is driven by the annual mean Hellerman and Rosenstein wind stress field, Levitus sea surface restoring temperatures, and Schmitt, Bogden, and Dorman freshwater flux fields (mixed boundary conditions) together with various parameterizations of Arctic freshwater export into the North Atlantic. The model simulations indicate the existence of self-sustained, internal variability of the thermohaline circulation with a period of about 20 years. Associated with the variability is a large variation in the deep-water formation rate in the Labrador Sea and hence the poleward heat transport in the North Atlantic. It is shown that the variability is insensitive to the freshwater flux and wind forcing used and that the timescale for this thermally driven convective/advective oscillation is set by the cooling time of the Labrador Sea. The variability is robust to various parameterizations of Arctic freshwater export but may be suppressed if there is a strong freshwater flux through the Canadian Archipelago (or equivalently, large precipitation) into the Labrador Sea. The importance of topography, although poorly resolved in this coarse resolution study, is addressed and the results are compared with a coupled atmosphere-ocean simulation and observations taken over the North Atlantic. ¿ American Geophysical Union 1994