| Popis: |
To estimate the mean circulation, water exchange and water agein the Gulf of Bothnia a ten-year simulation using a three-dimensionalnumerical model was carried out. The results confirmed the earlyfindings by Witting (1912) and Palmén (1930) that a mean cycloniccirculation takes place both in the Bothnian Sea and in the BothnianBay. However, the modelling results showed clearly that thereexist meso-scale circulation features including coastal "jets",not reported in the Witting-Palmén results. The simulated meancurrents were also higher than those found earlier, while thepersistency of this circulation is typically between 20 and 60%,which is similar to the earlier results. There is a large differencebetween the various model-based water-exchange estimates: theseare strictly dependent on the time-averaging used. Water ageproved to reflect properties of the mean circulation system,and the highest water age (of around 7.4 years) was found inthe central part of the Bothnian Bay. The water age was foundto be rather high also in the entire Gulf of Bothnia, which providesevidence of the rather slow water exchange between the Gulf andthe Baltic Sea. This leads to the conclusion that, from the physicalpoint of view, the Gulf of Bothnia is vulnerable to eutrophication. |
