The 12-box model of the world ocean proposed by Bolin et al. (1983) does not accommodate heat and salt conservation: whenever equations describing these constraints are added to those for carbon, nutrients, and mass, the advection flux between the Antarctic and the Atlantic becomes unrealistically small. This difficulty remains when the heat flux between the ocean and the atmosphere is considered unknown. Part of this is due to the design of the Atlantic surface ocean: there, heat release to the atmosphere requires downwelling, whereas outgassing rather requires upwelling. When this box is divided into two domains, one for the South and Tropical Atlantic, and one for the temperate North Atlantic, realistic upwelling and downwelling fluxes are obtained, but the small fluxes from the Antarctic to the Atlantic remain. Strategies for improving the design of the model are discussed.