During several cruises of r/v 'Oceania' in different seasons of 1993-1997 detailed investigations of the Pomeranian Bay were carried out with particular attention to the vicinity of the Odra river mouth. On the basis of CTD soundings as well as quasi-continuous profiling by means of a towed CTD probe, the thermohaline fields were analysed in order to determine the pattern of riverine water transport. The characteristic flow paths under different meteorological conditions were identified, Ekman transport of freshened waters being found to prevail along the coasts of the Pomeranian Bay.
Physical phenomena such as the pulsating outflow of the river Odra and the formation of isolated plumes of freshened water were observed. The vertical and horizontal extents as well as the lifetime and speed of movement of the plume-like structures were estimated. A typical plume was a few km in diameter and there were steep horizontal and vertical salinity gradients at the boundaries. As the plume moved away from the mouth, it was transformed and finally vanished.
There was strong wind mixing and entrainment into underlying, more saline water at some distance from the channel mouth. Hydrological fronts between riverine and ambient waters frequently formed. Numerous intrusions were found in the temperature and salinity profiles in the frontal zones. The freshwater fraction in the entire volume of the bay waters was estimated for different hydrological situations, the highest values being obtained for the period following the flood event of summer 1997.
Under favourable wind conditions, dense, saline waters flowing in from the Arkona and Bornholm Deeps were present in the near-bottom layer at the edges of the bay. Anomalously, waters of higher salinity were found in the Pomeranian Bay in November 1997 as a result of a minor inflow from the Danish Straits.