522
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
nuclear tests in 1954. The maximum fall-out corresponds to 1963. The function of atmospheric
input of 137Cs is plotted in Figure 5. The 137Cs records of the investigated sediment cores are
plotted against 210Pbex ages (Figure 6) calculated from the mean sedimentation rates listed in
Table 3. The top of the sediment cores was fixed to 1994. The two cores displaying the fastest
accumulation rates, from localities PM 9463-8 and PM 9482-1, show very good agreement
between the 210Pbex timescale and the first appearance of 137Cs. In the other 6 cores the
agreement is rather good. However, in these cores we detected 137Cs activities in layers older
than 1940 (dated with 210Pb e J, which are in evident discrepancy to the timescale of bomb
137Cs (Figure 5). This discrepancy originates either from a wrong (to small) evaluation of the
accumulation rate with 21OPb ex , or from postdepositional migration of 137Cs in the sediments.
The latter was suggested to happen in anoxic sediments (Evans et a!. 1983). As the sediments
from the shelf area become suboxic within few cm depth below the surface (Langner et a!.,
1995), we cannot exclude some migration of 137Cs to have occurred. Because of the larger
uncertainty of the accumulation rates from 210Pbex in these cores we cannot address this
question properly.
137 Cs FLUX
1
2
1972
1959~~=?
1954
Figure 5: Atmospheric flux of 137Cs in relative units (after Robbins and Edgington, 1976).
Standing Crop of 210Pbex
Comparison of the Standing crop of 210Pbex in cores with uncertain accumulation rates with the
one of core PM 9463-8 allows an additional test of their average accumulation rates. The
Standing crop (SC) of 210Pbex is defined as:
SC = J p(x)A(x)dx
o
where:
x : core depth [cm]
p: dry bulk density [g cm- 3 ]
A: 210Pb ex activity [dpm g-l]
(7)
In the other cores, where 210Pb does not penetrate as deep, we are aware that mixing may
significantly distort the depth profiles of 210Pbex ' In these other cores we evaluate the
accumulation rate by comparison of their SC with the one of core PM9463-8 under the
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
nuclear tests in 1954. The maximum fall-out corresponds to 1963. The function of atmospheric
input of 137Cs is plotted in Figure 5. The 137Cs records of the investigated sediment cores are
plotted against 210Pbex ages (Figure 6) calculated from the mean sedimentation rates listed in
Table 3. The top of the sediment cores was fixed to 1994. The two cores displaying the fastest
accumulation rates, from localities PM 9463-8 and PM 9482-1, show very good agreement
between the 210Pbex timescale and the first appearance of 137Cs. In the other 6 cores the
agreement is rather good. However, in these cores we detected 137Cs activities in layers older
than 1940 (dated with 210Pb e J, which are in evident discrepancy to the timescale of bomb
137Cs (Figure 5). This discrepancy originates either from a wrong (to small) evaluation of the
accumulation rate with 21OPb ex , or from postdepositional migration of 137Cs in the sediments.
The latter was suggested to happen in anoxic sediments (Evans et a!. 1983). As the sediments
from the shelf area become suboxic within few cm depth below the surface (Langner et a!.,
1995), we cannot exclude some migration of 137Cs to have occurred. Because of the larger
uncertainty of the accumulation rates from 210Pbex in these cores we cannot address this
question properly.
137 Cs FLUX
1
2
1972
1959~~=?
1954
Figure 5: Atmospheric flux of 137Cs in relative units (after Robbins and Edgington, 1976).
Standing Crop of 210Pbex
Comparison of the Standing crop of 210Pbex in cores with uncertain accumulation rates with the
one of core PM 9463-8 allows an additional test of their average accumulation rates. The
Standing crop (SC) of 210Pbex is defined as:
SC = J p(x)A(x)dx
o
where:
x : core depth [cm]
p: dry bulk density [g cm- 3 ]
A: 210Pb ex activity [dpm g-l]
(7)
In the other cores, where 210Pb does not penetrate as deep, we are aware that mixing may
significantly distort the depth profiles of 210Pbex ' In these other cores we evaluate the
accumulation rate by comparison of their SC with the one of core PM9463-8 under the