45 
It will not be easy to be able to foresee over 
which areas such a vertical transportation would take 
place, The sinking of particles (the first case) could 
take place in a restricted sea area; the eXchange of 
solutions (the second case) -— which is largely depen- 
dent upon current and diffusion processes —- can, on 
the other hand, extend over large sea areas, That 
would indicate that the material possibly released 
near to the bottom, would perhaps reach the surface 
at a great distancefrom the dumping area. In any case, 
one may then expect a high dilution of the pollution, 
We do not yet know which of the mechanisms will 
finally take effect for the transportation of the 
fallout products to near-bottom regions. Probably, 
both will occur simultaneously, whereby - according 
to sea area - the one or the other will predominate. 
Horizontal profiles 
If one considers the trend of the 15708 activi- 
ty concentrations in different depths along the re- 
spective profiles between the North Sea resp. the 
English Channel, and the Iberian Basin as far as the 
Azores, one can recognize the following:- 
In the year 1968 (Fig. 114), the North Sea 
surface concentrations lay at the levels of typical 
fallout values then normal for that area. In the 
English Channel those values rapidly diminished, 
and - in the Atlantic — lay at Just about half of 
the North Sea values, These concentrations were also 
in accordance with the fallout values normal at that 
time. In the mean, the activity concentrations at 
100 m depth lay only slightly below those at the 
surface. On the other hand, the concentrations at 
500 m —- and especially at 1,000 m —- stand out 
clearly in their levels from those in the upper 
water layers, 
The 900g activity concentration showed, 
With altogether lower initial values, practically 
the same trend (Fig. 115).