/6 
05.05. commencing at 12.00 hrs. to 06.05. at 16.00 hrs., with circa 
15 Bq/l-. 
On the Research Platform "Nordsee", the first increase was indicated 
on 06.05., at about 06.00 hrs. The corresponding activityconcen- 
tration lay strongly fluctuating at around 1 Bq/l. The essentially 
lower activity concentration in comparison to the other measurement 
stations, can be explained by the fact that hereby, in the first in- 
stance, the radioactivity must be down-mixed in the water column of 
15 m. By this dilution process, a lower activity concentration is 
detected by the measurement probe, than was oObserved at the other 
stations. The slow, further rise occurs owing to the contamination 
of the fouling covering of the measurement probe and indicated the 
progress of the enrichment and the desorption which follows after- 
wards, together with the radioactive decay of the accumulated radio- 
active substances. 
As examples of the activity increase in the DHI measurement network, 
the registrations from Light Vessel "Borkumriff” and Research Plat- 
form "Nordsee" are reproduced in Figs, 2 and 3. 
The Research Vessel "Gauss” was in the Baltic Proper at the time of 
the accident. The registration of the Gamma-radiation in the water 
at circa 4 m depth - in the working area of the ship southwards of 
Gotland - indicated an increased concentration of radioactivity from 
29th April onwards, with circa 8 Bq/l. At that time, no direct input 
by rain of the Fallout into the sea took place, It merely concerned 
precipitation from aerosol and fog. During the voyage out of the 
working area in the direction of Kiel, in the first instance a les- 
ser radiation level occurred in the water; from the Arcona Sea on- 
wards this level rose strongly on 10.05. with the set in of rain 
showers and, in the Kiel Fjords on 11.05. attained the highest value 
with a value corresponding to circa 9 Ba/l (Fig. 4). 
During a research ecruise with Research Vessel "Gauss” from 23rd May 
to 12th June (North Sea survey within "Circulation and Pollution 
Transfer in the North Sea), the distribution of the surface Gamma- 
radiation over the largest part of the North Sea could be ascer- 
tained. According to Fig. 5, it appeared that the highest input had 
taken place in the region of the Skagerrak, in the German Bight, and 
eastwards of southern England. Based upon the later radiochemical 
investigations of the water samples collected during this voyage, 
the increase off the region of the English coast was not confirmed. 
This increased registration of the monitoring equipment must evi- 
dently have concerned the registration of radioactivity of natural 
origin (Radon daughter products from rain resp. sediments resus- 
pended by storms)-. 
In total, the radiation level found exceeded only very little the 
natural deviations. During the "Gauss" research cruise from 20.06. 
to 17.07. over the entire North Sea no more significant increases 
were ascertained. 
The registrations of the radiological measurement network, it is 
true, can only offer a coarse, but quick survey of the occurrence of 
more strongly increased radioactivity in the sea. The effects of a@