73 
Results (G.A. Becker, H. Carlson) 
The vertical sections that were plotted from the 
STD - data show a predominantly thermo-haline strati- 
fication in the investigated area, The seasonal discon- 
tinuity layer is superposed to the vertical gradients 
generated by convergence. Therefore, the position of 
the frontal zone cannot be clearly determined, Deviating 
from theory (Takano, 1954) and from the mean situation 
in the frontal zone described by Goedecke (1951) the 
outflow axis of the Elbe water was found south of the 
island of Helgoland in the summer of 1976. A processing 
of a Landsat-2 image of 19 April 1976 (Krause, 1977) 
also revealed this atypical spreading of the Elbe water. 
It is supposed that persistent east wind situations 
lead to such a hydrographic situation. The water around 
Helgoland then contains high portions of Elbe water 
charged with pollutant and noxious substances. 
The development of vertical density gradients depends 
on the water depth and the tidal stream turbulence. 
During this investigation the transition from mixed to 
stratified water was found off the East Frisian coast 
at a water depth of 15-20 m; offthe North Frisian coast 
vertical density gradients were still observed at water 
depths of 10-15 m. The residual current which, in the 
mean, is running parallel to the coast and which trans- 
ports the lighter coastal water supports the density 
stratification here. 
During the three surveys the stratification in general 
changed only slightly, altheugh changes in the hydro- 
graphic situation were observed which were due to 
cooling at the surface and advective processes, as the 
TS diagrams (Figs. 12, 23, 40) show. From the TS dia- 
grams it may be seen that mainly three water masses