The high-resolution Princeton Ocean Model is used to simulate the circulation and seasonal variability of the South Atlantic Ocean. A diagnostic calculation, using the Levitus annual mean fields and forcing consisting of the climatological annual mean wind stress, produces a realistic steady circulation pattern. In particular, the meridional overturning cell shows equatorward flow in the surface and intermediate waters and poleward flow at depth. Associated with this circulation is a northward heat transport that reaches a maximum of 1 PW near 20 ¿S. The model results are improved when the density field near the ocean bottom is allowed to deviate from the Levitus values. Using forcing consisting of observed monthly wind stress, heat flux and a prescribed seasonally varying Antarctic Circumpolar Current (ACC), a prognostic calculation is next carried out to study the seasonal variability in the South Atlantic Ocean. With a realistic heat flux, the model output for the seasonal thermal field compares well with that in the Levitus data. An analysis suggests that the seasonal cycle of the Brazil Current separation latitude, as well as the strength of the Falkland-Malvinas Current depends more strongly on the prescribed seasonal variability in the strength of the ACC than on the seasonal variations in wind and buoyancy forcing in the South Atlantic. ¿ 1998 American Geophysical Union