The circulation in two water column thickness scenarios for Lake Vostok, a subglacial lake in central East Antarctica, is investigated using a three-dimensional numerical model. In a scenario with a constant water column thickness (the distance between the sloping ice sheet which caps the lake and the lake bed) the circulation is barotropic, but with a more realistic water column thickness the flow is baroclinic. The different circulations result from the geothermal heat flux warming shallow regions of the realistic lake more efficiently, thus forming a different horizontal density structure. The differences and uncertainties between the two scenarios highlight the importance that the largely unknown water column thickness and geothermal heat flux have in determining the circulation in the lake. ¿ 2001 American Geophysical Union