The time dependent 3-dimensional stratified Princeton Model was used, to analyse the dynamics in Belt and Sound. The Belt and Sound are narrow passages between the North Sea and the Baltic two regimes that have different density stratifications and sea level elevations due to different, natural processes in each basin. Three basic experiments were done. The first one of these is a two-basin experiment. Effects o f rotation, topography, friction, different stratification and barotropic forcing

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... re studied in these experiments, to analyse the water exchange and the control be tween the two basins. The flow has two distinct phases, one of them being linear adjustment in which Kelvin and Poincare dynamics set up the boundary and interior circulations, and the second being the nonlinear phase in which topographic effects and stratification play an important role and instabilities can occur. The heigh resolution in time and space of the m odel used here facilitates work on strait problems and the presentation of results. Several possible mechanisms of chan nel dynamics are presently under discussion. Some questions are, for example, which type o f control determines the dynamics in straits and gives the best prediction of the transport through a channel? Is the Rossby deformation radius important? Do barotropic or baroclinic processes play an important role? If both of them, how and when? W hy is the time dependent motion important? What are the effects of insta bilities and turbulence from the point o f view of energy propagation? Is it possible to see solitary waves, bore formations and also time dependent cylinders of rotating fluid in the system? Some of these questions are clear, but som e need some clarifi cations and further research. The second experiment is performed to determine the effects o f barotropic forcing on the stratified Baltic. The resulting circulations with and without barotropic forc ing both show expected, realistic patterns. The thermohaline circulation loses its two-layer character with barotropic forcing which is in these experiments given as a prescribed surface elevation at the boundaries of the model region. Unidirectional flow permits larger transport o f volume and salt than bidirectional flow in a channel.