surface were four to twenty times the lowest values
(48 counts per minute per liter of gross beta)
found
northeast of Bikini, where test contamination was
virtually absent.
Thus it appeared that the westward
fringe of the drift had reached,
in September,
the
vicinity of Guam, but at levels so low that they were
significant only for the purposes of identification.
Furthermore,
the maximum value
for water,
regardless
of place or depth of the sample, was 19,000 disinte~-
grations per minute of total beta, and this single
sample was taken from the surface at Station 2,
southwest of Eniwetok toward Ujelang Atoll,
cruise began.
as the
Levels of radioactivity diminished
sharply thereafter,
trailing off to the lower values,
while the samplings down to 150 meters were variable
in content and seemed,
as the report later stated,
fall into regional patterns.
surveys had discovered,
to
As all of the earlier
the Marsh also
found that
plankton were the most sensitive indicators of the
presence of radioactivity.
beta activity in plankton,
The highest value of total
21,000 disintegrations per
minute per gram, was found in samples taken eighty miles
north of Eniwetok,
and the
lowest,
27,
near Guam.
The
average of ratios of plankton activity to sea water
activity was 2,500 to 1, much lower than the ratio of
7,000 to 1 reported by the Walton three months earlier.
The Marsh survey between September 1 and 20,
1956,
completed the second phase of a two-stage study of a
radiation-tagged water mass.
It had found radioactivity