14 
о 
500 
1500 
2000 
С VI 
Bq/ kg d.w. 
1000 
Figure 3. 
Vertical distribution of Cs-137 
(Bq kg -1 d.w.) at some stations in the Bothnian Bay 
(CVI), Bothnian Sea (EB1), Gulf of Finland (LL3a), 
and Baltic Proper (BY15) in 2003. 
EB-1 
Bq/kg d.w. 
0 500 1000 1500 2000 
soft bottom station in the middle of the Gulf. In the 
Baltic Proper, the amounts of Cs-137 in sediments 
varied considerably, from 40 Bq nr 2 to 14 700 Bq 
nr 2 with a median value of 1 970 Bq nr 2 . In the 
Belt Sea, the Kattegat, and the Sound, the median 
value was 1 370 Bq nr 2 . 
The vertical distribution of Cs-137 in sediments 
(Figure 3) reflects large differences in the sedi 
mentation conditions at different stations, which 
depend on the bottom topography, sedimentation 
rate, bioturbation (which may partly explain the 
peak concentrations in the uppermost sediment 
layer), etc. 
LL 3a 
Bq/kg d.w. 
0 500 1000 1500 2000 
BY-15 
Bq/kg d.w. 
0 500 1000 1500 2000 
Depending on the method used (either 1:20 or 1:5 
for the total amounts on hard bottoms), the total 
inventory of Cs-137 in the seabed of the Baltic 
Sea was estimated at 2 100-2 400 TBq. This is 
about 8-9% more than in the previous evalua 
tion in 1998 (llus et al., 2003). The difference is 
explained by the additional new data, which have 
given greater precision to the calculations, and 
by the fact that Chernobyl-derived caesium has 
continued to be deposited onto the seabed. The 
inclusion of new data from the Gulf of Riga has 
also increased the total inventory. 
The inventories for the different sub-regions are 
given in Table 2. The dominant role of the Both 
nian Sea as an accumulation basin for Chernobyl 
caesium has continued to strengthen, amounting 
to 73% of the total inventory (1 530-1 740 TBq). 
The proportion occurring in the Gulf of Finland 
has clearly decreased from the previous estimate, 
while proportions in the Baltic Proper and the 
Bothnian Bay have increased slightly.