MODES OF STRATIFICATION IN A SEMIENCLOSED BAY AT THE NORTH SEA-BALTICSEA TRANSITION

Conductivity, temperature and depth (CTD) measurements were recorded w eekly at a fixed position in the shallow water of Arhus Bay over a per iod of 1 year. Variations in stratification and salinity are described in this study. Outflow of low salinity water from the Baltic Sea, and an estuarine return flow of high salinity bottom waters originating i n the North Sea were observed. Strong stratification occurs during spr ing, summer and late autumn, whereas stratification is weak or absent during winter. A stratification model in terms of the potential energy of the water column (phi) has been applied including wind, solar inso lation, estuarine circulation and current terms. Observations of strat ification are very well described by this model, although considerable differences were found to occur during a period of very strong strati fication. The interface is placed at a water depth of about 8 m during spring and early summer, and at a depth of about 12 m during autumn. A comparison of frequently used stratification parameters shows a high ly positive correlation between phi and the density difference between surface and bottom water. A positive correlation between phi and Brun t-Vaisala frequency was also found in periods of stable oceanographic and meteorological conditions, whereas no correlation was found in per iods of unstable conditions. (C) 1996 Academic Press Limited