Computations of the flow of dense water into the Baltic Sea from hydrographical measurements in the Arkona Basin

The dense water flowing through the Danish Sounds into the Baltic Sea creates a pool of dense water in the deepest parts of the Arkona Basin, just inside the sounds. The pool is usually thin since this basin has no sill in the east. The pool leaks and the leakage is assumed to be controlled by the vertical stratification in the Arkona Basin together with the rotation of the earth (rotational baroclinic control). For each instance of known vertical stratification in the Arkona Basin, the accompanying leakage may be estimated.

182 historical vertical hydrographical profiles taken in the Arkona Basin during a 25-year long period are utilized. The leakage of dense water is computed from each single profile. The estimated mean salt flux by the flow (from the Arkona dense pool) into the Baltic satisfies the continuity requirements for a stationary Baltic Sea. There is a positive correlation between the flow rate and the salinity of the dense water.

For a system where the salinity determines the density (brackish water), a dynamically equivalent, vertically homogeneous pool of dense water may be computed requiring conservation of profile salinity surplus Φ and profile potential energy PE. In this paper, it is demonstrated that Φ and PE completely determine the flows of volume and buoyancy (salt excess). Regardless of the actual shape of the vertical stratification, the volume flow is Q = PE/f and the flow of excess salt is QS = g∙β∙Φ²/(2∙f) where β is the salt expansion coefficient of sea water.