34
where variable levels of activity with depth would mask any
diurnal-nocturnal variation that might exist.
The change of relative radioactivity of the water with
derfth is variable but appears to fall into regional patterns.
It is likely that at the time of the Marsh survey those regions
containing the highest relative activity levels
in the deeper
layers were regions primarily affected by fallout, while those
regions having the bulk of the radioactive materials in the surface layer were regions to which the radioactive materials in
solution had been carried by surface currents.
It would follow
that by the time of the survey vertical mixing had not taken an
important part in redistribution of the radioactive materials;
possible exceptions may occur in the immediate vicinity of the
Mershall and Marianas Islands.
This interpretation which is based on the assumption that
most of the radioactive material went into either a true solution or a suspension of very small colloidal particles soon
after fallout is supported by the fact that most of the activi-
ty passes through a Millipore filter (Table 3).
However, dif-
ferences in specific gravity of the particles would result in
the same type of distribution.
It is possible that relatively
higher values near the surface for stations to the westward are
accounted for,
in part, by fallout of lower specific gravity
than that of fallout nearer the test site.
The particles of
lower specific gravity would be assumed to have gone into com-
plete solution while still near the surface.