}#* 
This finding can be explained by the intensificati1ion of the ecircula- 
tion in winter as a result of the winterly strong wind conditions 
and the increased frequency of storms. 
This leads to & shortening of the turnover times and to an intensi- 
fied large-scale mixing. Both contribute to a concentration decrea- 
se. The cause of the seasonal variations, in the last analysis, lie 
in the annual variation of the wind over the North Sea, which drives 
the ceirculation with different intensities., The annual variation of 
the wind are superimposed by considerably shorter-periodic varia- 
tions, which are typical for the course of the weather over northern 
Europe, The variations calculated reflect the natural, weather- 
dependent fluctuations of the North Sea system. 
The high summerly concentrations in the North Sea wander with the 
circulation alongside the econtinental coast. Off the coast of 
Jutland (Fig. 11d), therefore, the maximum values occur rather in 
winter. This is explained by the fact that the currents need about 
six months in order to entrain as far as off the coast of Jutland 
substances which were introduced into the southern North Sea, As 
there (in our model) is no source, the cöncentration encountered 
here is to be traced back to the sources in the southern North Sea, 
A comparison of the concentration variations in the individual box- 
es, clearly indicates that, for example, extreme values were not en- 
countered simultaneously in all boxes. The temporal course and the 
structure of the variations vary from box to box. The main reason, 
however, lies in the regional varlability of the processes which in- 
fluence the eirculation. Primarily, this is the wind, but also the 
tides and the distribution of mass of the sea. 
5 
Consequences from the results for the monitoring of pollutants 
From the model results, especially from the concentration varia- 
tions, conclusions must be drawn for the monitoring of the sea. 
In the following, an example is used to demonstrate to what monito- 
ring results non-spatially resp. non-temporally f£fitted monitoring 
strategies lead. 
It is presumed that the boxes 4 and 5 in the region of the German 
Bight are examined only once per year - at intervals of one year — 
for their content of pollutants (see Fig. 1lla). From the relative 
concentration variations shown in Figs. 1lb to d, one can now take 
the “results” direct. The hypothetical "result” still only depends 
upon the choice of the monitoring time. Just as one monitors in win- 
ter or in summer (or also at other seasons), one reaches different 
results for the German Bight. The two different results of a yearly 
monitoring, with a 6 months temporal phase shift is shown in Figs. 
12a, b. In the Figures, the relative percentage loads are shown from 
a monitoring in winter resp. sommer. 
The course of the curves indicate not only different variations but