43 
took place down to 100 m depth. At 500 m depth, there 
was again about the same concentration as at the sur- 
face; at 1000 m depth, the value lay again at about 
40 % higher, Only from 2,000 m depth downwards could 
one again observe activity concentrations at the same 
levels as those of the other stations. Unfortunately, 
there are no 900g measurement values available from 
this vertical profile. 
A comparable vertical distribution of !?7cg 
could be observed on 4th August, 1972, at a station 
at 50° N 15° W (Fig. 111). Thereby, the concentration 
at 1,000 m depth rose to over double that present at 
the surface, however, showed -—- below 2,000 m —- the 
same trend as those of the aforementioned stations, 
Ihe vertical distribution of the ?°sr activity con- 
centrations at this station showed practically the 
same trend; that is, downwards to the depths there 
was no increase in concentration to be observed 
(Fig. 112). This clearly shows that this results 
from the isotope relationship 90gp: 13705 in the 
different depths. At the surface it was 1:1.4, 
and 1:5,3 at 1,000 m depth. We had already observed 
a comparable occurence in 1970 at a station in the 
western Mediterranean Sea (Kautsky 1977). 
These results indicate that - under certain 
conditions —- the concentrations of 15708 and 909 
in the Mediterranean can be differently influenced, 
The local enrichment of 15708 measureable in certain 
depth horizons, in contrast to 908, suggests the 
possibility of the effect of biological mechanisms. 
It is known that 908 does not normally accumulate 
in plankton or other marine organisms, but on the 
other hand, that 15708 can do so to a certain degree 
(up to about a factor of 100). 
The 15708 activity concentration values in 
surface water had not changed in 1974 when compared 
with those of 1972. Down to 500 m depth, the values 
- within the framework of the usual deviations —-