A fine-resolution primitive equation model is used to investigate the seasonal variability of the interocean mass exchange via the Southern Ocean. The meridional overturning is calculated on both depth levels and density layers. The interocean mass exchange is estimated from the meridional stream functions in the different oceans. The annual average is found to be mainly governed by the thermohaline circulation in the so-called oceanic conveyor belt. The seasonal variability is mainly due to changes in the wind stress, which are not necessarily local. The largest seasonal variability is found in the Pacific Ocean around 30°S and around 34°S in the Indo-Atlantic. In the Indo-Atlantic there are two meridional cells merged into each other at the surface, but driven by the northward Ekman transport at two different latitudes. The deepest one, which is part of the conveyor belt, has a seasonal variability driven by the changes in the northward Ekman transport at 35°S. The shallower one (Deacon Cell) is driven further south at 43°S, where the zonal wind stress reaches its maximum. Simple relationships with the meridional Ekman transport, the meridional thermohaline transport, and the total interocean exchange of water masses are found among the three world oceans. The meridional stream function, simulated by an analytical model, shows that seasonal variability of the fine-resolution Antarctic model is barotropic and its baroclinic circulation is mainly stationary.