20
19
(pCi/g) associated with the fine material at various depths in the
sediment column exceeds the concentrations associated with the coarse
components in both cores, the inventory of the radionuclide (pCi/em)
within any depth interval assocfated with the fine and coarse components
can be variable throughout the sediment colum.
Areal transuranic
deistributions like those shown in Figs. 2 and 3, but associated with
only the fine or only the coarse component of sediment, would differ.
The vertical distributions of the transuranics in the Lagoon
sediment are very complex.
No generalization about the shape of the
concentration profile in any region can be made.
shows a
241
Table 2,
for example,
Am peak associated with the fine components of core 6 at
depths of 25 to 30 cm with little 2a associated with the coarse
components at these depths.
In core 1,
the highest 24d concentrations
are associated with the fine components between depths of 8 to 10 cm in
the sediment column,
The 24d concentrations associated with the
coarse component in both cores generally decrease gradually with depth.
fransuranic concentrations increase, decrease, or remain constant with
depth in sediment cores from other lagoon locations
(No78a).
The
concentrations of 23942405, and 241, associated with the carbonate
components in four cores taken along a 1,5-km transect across Mike and
Koa Craters are shown in Fig. 6,
The concentrations in the sediments
from the Atolls’ largest craters are surprisingly nonhomogenous,.
Turbulence and large scale mixing of the sediments during and after
testing should have produced a much more uniform distribution than that
found.
The
239-240
Pu concentration in the sediment column at station
17E is fairly uniform to a depth of 50 cm,
At station 16E,
concentration increases with depth to 35 cm.
The
241
the
Am concentration in
the sediment column at station 16E decreases with depth.
No correlation
igs obvious between the PALay and 2394240Pu concentrations associated
with the components of these crater sediments.
The craters should act
as natural sediment traps but little sedimentation in the Mike and Koa
craters has occurred since the bottom depths were redetermined in 1964.
In 1964 the maximum bottom depth of Mike Crater was 27.4 1 below sea
level (Ne73),
We have found no measurable change in the depth of the
crater bottom during the period 1972-1977. Only small quantities of
resuspended or reef-generated particulate material are then transported
in the water masses to the western reef.
Very little sedimentary
material therefore escapes from the lagoon and any resuspended bottom
material probably settles out again on the lagoon floor close to its
origin.
The complex areal and vertical patterns of transuranics
detected in this relatively small region of the lagoon where the
distributions are expected to be more uniform are but examples of the
complex patterns in the lagoon.
Halimeda,
shells, coral, and foraminifera fragments were sorted
from the coarse fraction of several sediment samples by hand.
Table 3
shows the 23942405, concentrations associated with each component in the
surface layer from two locations in Enewetak Lageon and at various
depths in a core from Bikini lagoon.
The 23942405, concentration
associated with Halireda fragments at station 40C only slightly exceeds
those in fragments from station 3D.
The concentrations associated with
por ARCHIVE