Once the radioactive materials have been absorbed
or adsorbed by the plankton, their distribution is
likely to be greater both vertically and horizontally
than if distribution were solely dependent upon the
surface currents.
One reason for a greater distri-
bution would be that absorption by plankton makes the
radionuclides available to larger organisms which can
move beyond the current's boundaries.
Similarly these
materials also become available to the local resident
populations and,
as they are recycled through the food
chain, the effect is a delay in their distribution away
from the original area of contamination.
Another factor
influencing the distribution of radioactive materials by
plankton is their diurnal vertical migration.
If this
migration were great enough to take the plankton below
the current stream,
it would extend the vertical distri-
bution and also slow down the horizontal distribution,
because the plankton would be moving horizontally more
slowly than the water.
Plankton may carry radioactive materials from the
deeper waters of the lagoons to the surface or even up
onto the reefs and eventually to the islands by vertical
Migration.
At Bikini it has been observed,
for example,
that these materials were picked up by the plankton in
the deeper waters of the lagoon during the daytime.
The
concentrated radionuclides in the plankton were then
transported to the surface by the diurnal vertical mi~
gration of these minute forms.
At the surface,
their
presence at night caused the surface radiation content
to increase measurably over the daylight readings.
The