4
¢
ce ta eee
ae
Bie5:rR
Ea
that the vessel traversed the north equatorial
current at three distances west of Bikini. In
the course of these traverses, the Japanese
scientists obtained water samples at various
depths and from their data have constructed the
profiles showing contamination with depth at each
of their traverses,
as Exhidit B,
These profiles are attached
3. The Japanese data are consistent with our
data obtained during CASTLE whioh indicate that
diffusion occurs rapidly between the surface and the
thermocline but that exchange with water below-the
thermocline takes place very slowly.
Moreover,
tritium measurements of ocean water by Dr, Willard
F, Libby, while at the University of Chicago, suggest
that material distributed between the surface ard
thermocline are diffused with e halflife of about 18
we eneeea 8
years,
This exceedingly slow rate is exolained ty
the surprisingly small coefficient of exchange across
the thermocline,
“ aeAeeee went.
4, The Japanese data also suggest that lateral
diffusion from the equatorial current is likewise
proceeding at a slower rate than would have been
expected on the basis of previously available
knowledge.
5. The Japanese data have been reviewed by oceanographers from the Woods Hole and Scripys Institute of
Oceanography and the AEC technical steff.
In their
opinion a large part of the radioactivity observed in
the North Equatorial current will eventually flow
into the Kuroshio current in the manner illustrated
in Exhibit C which projects the course of this
activity for the next few months.
The diminution in
activity between the end of June when the Japanese
made their last survey and 1 March 1955 would be in
the order of 90% due to radiological decay and oceanographiec factors,
This presents us with the
possibility that large masses of the equatorial and
Kuroshio current may continue to be radioactive in
amounts which do not necessarily constitute a heelth
hazard but which are certainly high enovgh to attract
the attention of Japanese scientists,
6, The radioactivity of the Kuroshio current to the
west and north of Guam snould be assessed.
In order
to facilitate monitoring of these waters an epprovriate
vessel is needed to sail frcm Guam on or shortly efter
1 March 1955 on a reconnaissance
of Far Eastern waters
for a duration of two to four weeks,
We would assign
six scientists to this vessel and would make available
certain laboratory equipment by which samples could be
obtetned and their significance assessed on a current
basis.
Tne course of the vessel should approximate
that shown in Exhibit C but operational flexibility
should be provided and the actual’ course determined by
the day to day research findings of the scientific
staff assigned to the mission,
x
Enclosure I
ue we
yeOy