te radioactive material accounted
\jor part of this activity was conline. Fig. 3 shows the percentage
ticulate form at different depths
two samples collected within the
f particulate radioactivity in the
ose slightly at 48 hours. However,
1m) and inside the thermocline
-rose at an increasing rate during
he percentage of radioactivity in
xponential rate from a value of
48 hours.
ig edges of the particulate radio-
i, and those of the soluble-colloidal
ie 28—48 hours the leading edges
ity in the mixed layer descended
ie mixed layer during the entire
vpproximately 2.5m per hour.
oactivity in the particulate form
in the mixed layer. During the
ity moved down at least 200 m,
or approximately 10 m per hour. This mayreflect the separation of the particulate matter into a heavier fraction, which was observed at 6 and 28 hours as
deeper concentrations of radioactive particles and which sank below the mixed
laver ahead of the remaining particulate activity. During the last 20 hours
the heavier particles descended rapidly through the thermocline.
The failure of the radioactive contamination to become evenly distributed
throughout the mixed layer might be attributed to the short duration of the
observations on the movement of the radioactive material in the water,
although this is probably not the case. In the area of the test site, at least, the
combination of the effect of gravity on the particulate activity plus the rapid
movement of the surface waters (above 25 m depth) tends to cause stratification in the mixed layer of sufficient magnitude to overcome, in part, homogeneous mixingin this layer. The ability of phytoplankton to concentrate radioactive materials and to remain near the surface probably adds to the tendency
towards stratification in the mixed layer.
Homogeneous dispersion of the radioactive contamination throughout the
mixed layer may occur after sufficient time has elapsed, as indicated in the
WALTON SURVEY (JUNE 11-21, 1956)
4 DAYS TO 23 DAYS ASTER CONTAMINATION
‘ «MARSH SURVEY { SEPT. I-20, 1956)
6 WEEKS AFTER ENO OF TEST SERIES
-21, 1956)
IR CONTAMINATION
~-+-~ COLLET? Survey (auG. 3-14, 1958}
AT END OF TEST SERIES
nee SILVERSTEIN SURVEY (SEPT 2-13,1954)
a WEEKS AFTER ENO OF TEST SERIES
-20,, 1956)
TEST SERIES
a-14, 1958}
TES
RANGE OF UPPER ECGE
QF THERMOCLINE
sEPT. 3-13, 1958)
OF TEST SERIES
19,000
.
9,000 +
8,000
E 7,000
>
-
uw
=
=
a
=t
[tg
6,000
r
5,000
4,000 }-—
3,000
2,000 F.
teu
VALUES
MULTIPLY
7000+ *
300
ES
400
_ soluble plus colloidal fraction in all
cing 1956 and 1958 between the EniGuam
0
2550
100
180
200
250
300
ano
DEPTH IN METRES
Fig. 5
Total radioactivity in water samples from four oceanic surveys made during 1956 and
1958 between the Eniwetok Test Site and Guam
§
113
“nf