Lake Vostok, isolated from direct exchange with the atmosphere by about 4 km of ice for millions of years, provides a unique environment. This inaccessibility raises the importance of numerical models to investigate the physical conditions within the lake. Using a three dimensional numerical model and the best available geometry, we analyse the baroclinic flow and the tracer dispersion within the lake. From our model experiments we find a different representation of the flow regime in the northern and southern basins of Lake Vostok, closely correlated to bedrock topography, ice draft, and the melting/freezing pattern. The time needed for tracers to dissipate across the whole lake is strongly dependent on the location where they are released and amounts from years to decades.