In the Weddell Sea oceanographic data and numerical models demonstrate that Ice Shelf Water,one ingredient in the production of Weddell Sea Bottom Water, is formed by thermohalineinteraction of High Salinity Shelf Water with the base of the Filchner-Ronne ice shelves. South ofBerkner Island a passage with a water column thickness of about 300 m linking the Filchner andRonne regimes is important for the ventilation of the sub-ice shelf cavities. To simulate the flow wetested a two-dimensional thermohaline criculation model on several sections which approximatedifferent geometries of a sub-ice shelf channel bounded by the ocean bottom and the ice shelfbase. Temperature and salinity profiles measured in front of the Filchner-Ronne ice shelves areused to force the model. The results indicate that the circulation is sensitive to both salinity(density) forcing and depth of the shelf bottom prescribed at the open boundary representing theRonne Ice Shelf edge. Where the shelf is shallow, 400 m deep, a closed circulation cell within theRonne cavity acts like an ice pump with accumulation rates of marine ice at the ice shelf base upto 1.5 m/a. The total outflow at the Ronne Ice Shelf edge is supported by an inflow from theFilchner regime. Where the shelf is deeper, a flow from the Ronne into the Filchner cavity developsif the bottom salinity at the Ronne Ice Shelf edge exceeds a critical value of 34.67. Seasonalvariability imposed at both edges modifies the circulation pattern at the Filchner Ice Shelf edgesuch that the depth and magnitude of Ice Shelf Water outflow correspond with observations in theFilchner Depression.