14 
Introduction 
Decisive for the transport of pollutants in the North Sea are prima- 
rily the currents (circulation). The first experiments for the in- 
vestigation of the ceirculation of the North Sea were carried out at 
the turn of the century (Fulton, 1897; Bidder, 1906). From measu- 
rements of the salinity from the years 1902 to 1914, Böhnecke 
(1922) derived a first complete, severely simplified, eirculation 
pieture of the North Sea. He realized that seasonal changes of the 
circulation occur. The basic pattern of the eirculation is described 
as follows: 
Northwards of Scotland, Atlantic water penetrates into the North 
Sea, moves southwards alongside the East coast of England, and mixes 
wich Atlantic water from the Channel, then along the North coast of 
the Continent - through the German Bight and alongside the west 
coast of Jutland - after a detour through the Skagerrak, to again 
leave the North Sea on the west ecoast of Norway. 
The tidal wave entering from the Atlantic transmits itself in the 
North Sea, in the same manner - eycloniec, in the form of a Kelvin 
wave. The sea levels and the current velocities increase from the 
middle of the North Sea towards the coasts. 
Although small-scale structures in the eireculation of the North Sea 
were observed in the first half of the twentieth century, detailed 
information about them have only just been compiled by different ex- 
periments (e.g@g,. JONSDAP; INOUT; and model simulations) during the 
last decade. 
The eirculation of the North Sea is essentially determined 
bhv 
Shape and depth distribution 
Tides 
Meteorological Influences, 
such as air pressure and wind 
Stratification 
Numerical models have been developed since the middle of the nine- 
teenfifties. Today, they have reached a state which permits the dif- 
ferent factors that influence the circulation to be investigated 
more exactly. Above all, models offer the possibility of synopti- 
cally taking into consideration the ceirculation in the whole of the 
North Sea. With measurements this is very difficult, because they 
can only be carried out at a few positions and never in the whole of 
the North Sea at the same time. 
The results of the numerical simulation of the North Sea eirculation 
are shown in Figs. la to d, as well as 2a, b. In Figs., la to d, the 
different current directions and velocities in summer and winter are 
ghown. In contrast, Figs« 2a, b show an annual mean of the eireu- 
lation for the surface and the 3rd model layer (20 m to 30 m). The 
results of numerical models depend upon the choice of the numerical 
grid. The finer the lattice (horizontally and also vertically), the 
more small-scale structures of the current permit themselvess to be