13 
at the coasts, in water input from land, but also in the volume in 
the smaller water-body of the shallow water region. 
The measurement values, owing to the activity ratio between Cs 134 
and Cs 137 are to be clearly recognized essentially as the result of 
the input from the accident at Chernobyl, because the ratios thereto 
lie between 0.41 and 0.60. 
At the beginning of June, the investigation of the beginning of May 
described was repeated by the Research Cutter "Victor Hensen”". 
Hereby, water samples from deeper water layers could be taken, in 
order to realize the vertical transport of the radionuclides. As can 
be seen from Fig. 16, the contamination reached deeper water layers 
down to about 20 m owing to vertical exchange. The conditions could 
be very severely influenced by a discontinuity layer built up during 
the early summer in about 25 m depth. 
The investigation of the large scale distribution of the contamina- 
tion in the whole of the Baltic Sea region was carried out in inter- 
national co-operation during a RV "Gauss" voyage in October/Novem- 
ber. The analyses of the samples from that cruise, at the moment of 
compiling this Report, are not yet completely concluded, Never- 
theless, one can infer the large-scale distribution by the gamma- 
spectrometric analyses of ion exchanger samples during the voyage. 
The highest concentration was observed in the region of the Aaland 
Sea, with more than 500 mBq/l Cs 137 (Fig. 21). The concentrations 
decrease in the northern direction, and - in the northernmost part 
of the Bottenwiek - attain an astoundingly low value of 24 mBq/l 
Cs 137. The southern part of the Baltic Sea between the Sund, Born- 
holm, and the Danzig Bight, in the northern extent as far as sou- 
thern Öland, there was widely constant lower contamination of around 
35 mBq/1. The concentrations first begin to rise again in the direc- 
tion of the west. 
As soon as the whole of the data material of the Baltic Sea voyage 
o£ RV "Gauss"” is available, it will be published elsewhere. 
6.3 North Sea region 
On a voyage of the Research Vessel "Gauss” from 23.05. to 12.06. 
samples were likewise taken in the North Sea for the determination 
of Radiocaesium on a large scale. The route of the voyage and the 
results are shown in Fig. 17. As already described in 4.2.2.1, the 
additional input of activity owing to Chernobyl can be identified 
from the course of the isolines of the activity ratio Cs 134/Cs 137. 
Owing to the slight previous burdening of the North Sea with Cs 134, 
above all, this distribution reflects the Chernobyl input. The 
Cs 134 depth distribution indicates that the surface measurement 
data are to be viewed as being representative for the mixed layer. 
The thickness of the mixed surface layer is known at the time of the 
investigation owing to the accompanying oceanographic measurements.