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are responsible for the hydrographic structure of the 
investigated area. These are: 
coastal water 
North Sea water of the surface layer 
North Sea water of the bottom layer. 
Off the East and North Frisian tidal flats separate 
water bodies were partly encountered which, due to the 
limitation of the investigation to water depths of 
more than 10 m, cannot be clearly characterised. 
The recordings of the thermistor chains moored in the 
area of investigations (Fig.53,54) give an insight into 
the variability of temperature stratification. The 
series reveal vertical movements (internal waves), 
heating and cooling processes, periodic horizontal 
water movements ({(tides), aperiodic horizontal water 
movements (advection) and, especially towards the end 
Sf the series (from about 7 Sept.) vertical mixing 
processes. To separate the individual processes within 
the series does not seem possible, or only to a certain 
degree. Qualitatively, the series immediately suggest 
that 
the correlation between the two stations is 
very high; 
che amplitudes of the internal waves (internal 
tides) have their maximum in the discontinuity 
layer: 
the amplitudes become smaller with decreasing 
stratification, and vanish on about 9 September 
1976, due to increased influx of kinetic energy, 
Like the thermistor chains the current measurements 
also show that the semi-diurnal tide {M,) is the