736
Noshkin et al.
Table 5. ™Sr and *’Po (**Pb) concentrations,
decay corrected to year of growth. Unsupported
and supported ''Am concentrations.
StL
Unsup.
1971-1972 9.09451
1970
_
Ar
Sup.
0.00
0.00
G.01
G.02
0,02
1963
0.0742
O.11
1960
1961
1960
1959
195€
O, 30461
0.05453
9.40433
1.85417
1957
0. 93425
1956
4b +f
1954-1955 1.4 413
*Unsup:
lost
—
0,09+37
oO.L7#hd
0.13439
G. 12436
©.12+52
O.52413
99. %
9.00
1969
1968
1967
1HE
1965
1964
"4
ky
pCi/e dry weight + 7 error
Estimated
year of
growth
Pacific (North equaOcean torial current)
0.45412
69. 78412
0o.T71+4
0.6946
0.7246
0,.89+h
O.10
2.1545
1.0345
lost
O.19+5
0.1546
0.1945
0.2045
0.22412
9.2149
0.20
0.25425
9.19410
1.44
16.042
o.k8+th
O.45
a.28
2.3623
8.6843
O.42
4.6
16.1
33.341
32.241
39.341
Pu decay.
Sup:
n
Ko
Atoll
reservoirs
Bikini Lagoon
i
Ny
0.1945
1.2144
1.7543
unsupgpyted 2blamn.
supported by 2
a4
00 F
0, 2449
0.29422
0.2517
1.04211
1.3559
|
ky
Ocean
Fig. 6. Box model diagram of Bikini Lagoon
describing the general flow and sources of radionuclides into and out of the lagoon.
see 24lam
tbetermined by beta counting 7°y - daughter of
90sr on low-level proportional counters.
#210py activity determined by counting <l°Po
using alpha spectrometry.
the concentration (pCi g-!) in the annual
growth bandis proportional to the concentration in the adjacent environment. On
this basis, we find that all detected radio-
side and east of the lagoon. Radivelements
6Co, *°TBi, *41Am, and !°Eu were not de-
' tected by gammaspectrometry in any water samples collected outside the atoll but
were prominent in biota and sediment sam-
ples (Fig. 1, Table 1) from the lagoon. We
conclude that the atoll is the principal
source of radionuclides to the lagoon en-
vironment.
Our investigation differs from others at-
tempting to use corals to determine the
trace element composition of adjacent waters. We are not comparing concentrations
from different species or concentrations in
whole specimens from different areas. We
expect coral samples from different lagoon
locations to have significantly different absolute
radionuclide
concentrations,
and
preliminary data have verified this assumption. Having only a single sample from one
location, however, we need only assume for
each element or radionuclide that each
vearly increment of coral growth concentrates the same available fraction from
seawater per unit weight of coral; then,
nuclides (except 7!°Po) have decreased in
the lagoon by twoto three orders of magnitude since the test years.
The rate at which the radionuclide concentration changes with time is not constant. The rate of change was most rapid
after the test series. In some years (e.g.
1964 compared to 1963 and 1965), the concentrations of some radionuclides changed
abruptly: for these small but real changes
we have no explanation. Wetried to correlate the 1964 increase with the peak in
fallout deposition in the Northern Hemisphere, but the computed amount depos-
ited in the lagoon in this period wasinsignificant compared to the observed change.
Although these data are derived from only
one coral collection, they suggest that unanticipated processes in the atoll may lead
to abrupt changes in the concentrations of
specific radionuclides in the lagoon environment. However since 1965 the concentrations of many specific radionuclides have
decreased only slowly (after correction for
decay}; this indicates that recycling from
sedimentary processes, biological activity,
2
ys a
muy