A circumpolar model for regional studies of the wind-driven and thermohaline circulation of the Southern Ocean including the major sub-ice shelf areas is described. A first series of numerical experiments focusing on the Weddell Sea reveals a pronounced and persistent double-cell structure of the Weddell Gyre with a maximum transport of ~60 Sv, in agreement with observations. Experiments with artificial passive tracers point to the shallow shelf areas off the Filchner-Ronne Ice Shelf as main locations for bottom water production. The trajectories of Lagrangian floats are used to determine the pathways and timescales of water mass spreading in the model. In addition, the effect of sub-ice shelf forcing on the water mass characteristics is evaluated. It is shown that water modified in the sub-ice cavities contributes significantly to the deep and bottom water formation along the continental slope, and affects the water mass characteristics throughout the Weddell Sea, by increasing the stability of the near-surface stratification and preventing deep convection. ¿ 1999 American Geophysical Union