Kb 
water from the rivers Weser and Elbe, higher values continued to be 
observed. These facts of the case became particularly clear (Fig. 
22) owing to the follow-up investigation in December. The activity 
ratios between Cs 134 and Cs 137 permit the recognition of the 
Chernobyl Fallout essentially in the eastern part of the German 
Bight, whereas the activity ratios in the northwestern part - in 
spite of higher Cs 137 values - permit the conclusion that the 
contamination found here are to be traced back rather more to the 
discharges from Sellafield Works or La Hague- 
After the initially higher values of the Baltic Sea surface water 
near Fehmarnbelt on 5th May, the activity concentrations decreased 
relatively rapidly until the middle of June. Hereby, the processes 
of the mixing of the water column with subsequent lateral inclusion 
of the bights and - later - the open Baltic Sea predominated. Since 
July, a further receding of the activity concentration can hardly be 
seen. Most obviously, one can recognize a reduction in the part open 
to the Baltic Proper (Figs. 15, 16, 20, and 21). In order to trace 
the development further, the regular Caesium determinations must be 
»ontinued above all in this region (Fig. 14). 
5 
„2 
Baltic Sea region 
Before the accident, the concentration values of Cs 137 in the sur- 
face water of the Baltic Proper lay at circa 15 mBq/l. As far as 
into the region of the Western Baltic Sea, the concentrations in- 
creased to about 35 mBq/l due to the influence of Sellafield Works. 
For that reason, Cs 134 was only to be found in this region in very 
slight activities. The determination of the part of the Cs 134, par- 
ticularly in the Baltic Sea, offers the opportunity of being able to 
identify the Chernobyl Fallout during the years to come. 
In Fig. 15, the Cs 137 activity concentrations of the surface samp- 
les are entered, which were taken on the return voyage of the Re- 
search Vessel "Gauss” from the working area in the Baltic Proper 
immediately after the accident. The values gained correlate well 
with the registration of the Gamma radiation measurement probe on 
board (Fig. 4). At the time of the ship's arrival in Kiel, at the 
same time a sampling by SWS "Atair” was carried out from the Little 
Belt to the Lübeck Bight. 
Owing to the fact that during the "Gauss” voyage it did not rain in 
the Baltic Proper at the time of the investigation, the contamina- 
tion of the sea in this region took place exclusively by aerosol 
precipitation. From the considerable height of the activity in the 
surface water, a very high air activity is to be inferred in this 
sea region. On the return voyage to Kiel, the ship left the region 
of more highly contaminated waters. The increasing activity concen- 
trations in the Western Baltic Sea are to be explained as being 
owing to rain precipitation towards the journey's end of the ship. 
The very much higher concentration near the coasts is conspicious. 
The reasons herefor could not only lie in the heavier precipitation