and Sb'*5 contributed 30 to 40 percent of the total activity associated with a mixture of sand and
water from the sediments. The rare earths and Ru! contributed the remaining activity. The
strontium, cesium, and antimony were dissolved in the water associated with the bottom sand,
but nevertheless appeared to be trapped within the sediments. One sediment water sample col-
lected off Site Charlie 4 May 1956 and analyzed 15 May 1956 assayed 2.5 x 10° dis/min Sb!" and
5 x 10° dis/min Cs'"7 per liter. Immediately following Cherokee no change was detected in the
Bikini Lagoon sediments.
Subsequent to Shot Zuni, 28 May 1956, young fission products were detected in the western
portion of the lagoon, with the older Ce’ and Ru’still predominating. Table 5.5 presents an
analysis of the bottom water and sediments from the southern portion of the lagoon following
Shot Zuni. About 90 percent of the activity is associated with the finely divided particulate
matter stirred into the water during collection, with less than 10 percent associated with the
coarse coral particles in the 10-to-1,000-micron range.
During the Redwing testing, the shells from living organisms in Bikini Lagoon displayed pre-
dominately the pre-Redwing fission products Ce!and Ru, Coral skeletons also showed Ce!“4
Ru!® Mn**, and Zn®* of the order of 1 to 20 dis/min of each isotope per gram. Onthe other
d
hand, corralline algae and green algae growing on the above shells and coral showed the presence
of Ce!) Rut} 731) pal and Zr*® immediately following Zuni and subs2quent shots.
3.6.5 Pelagic Sediments. A survey of the background radioactivity of the pelagic sediments
throughout the EPG in April 1956 prior to Redwing showed widespread artificial radioactivity on
the ocean floor in the survey area between 162° and 170°E and between 10° and 15°N. Ru’and
Ce’ were each present in quantities amounting to 10 to 1,000 (dis/min)/cm? of the oceanfloor.
Traces of Sb'?5, Zn®5 and Mn* were also detected.
Sediments collected northeast of Bikini Atoll in the vicinity of 13°N and 165°E following Shots
Zuni and Flathead (12 June 1956) showed no detectable recent fission-product activity. The pre-
dominentolder Ru!® and Ce'*4 may have obscured 1 or 2 percent of any recent addition of Ce'*!
Ru!3 and Zr*®,
’
During the Equapac cruise in August 1956, sediment cores were taken at 6° 30'S 164°E: 5°S
156° 20’ E; 2°S 157°, 0°S 157°E; 11° 43’N 166° 15’ E; and 11° 44°N 166° 13’E. South of the
equator, no fission-product activity was detected above the lower limit of detectability of 2 +2
dis/min Ru'*/em?, A trace of Ce!#4 and Ru'® of the order of 2 to 6 (dis/min)/cm? was observed
at 0° 157°E. At 6°N 157°E, 15 dis/min Ce'Ycm? and 18 dis/min Ru!°Ycm? were detected. A
core collected north of Ailinginae Atoll at 11° 44’ N 166° 13.5’ E on 4 September 1956, assayed
on 6 March 1957, 470 dis/min Ce!‘ and 252 dis/min Ru'/cm? of ocean floor. No evidence of
fission products originating during Redwing was detected in the Equapac pelagic sediments within 6 weeks following Shot Tewa. Figure 5.7 shows a typical gamma energy spectrum of a deep
sea sediment collected in the EPG immediately following Operation Redwing.
No sediments were collected in the area of maximum fallout north and northwest of Bikini
Atoll after cessation of the Redwing series. There is insufficient data to determine the time of
arrival of fallout on the ocean floor.
Bottom samples obtained south of Eniwetok Atoll in the vicinity of 11° 18’N, 162°57’E during
December 1956 and assayed 1 June 1957 showed an average of 60 dis/min Ru!&/cm? and 14 dis/
min Zr*/cm?. A sponge obtained from the same area assayed 10,000 dis/min Ce'“*, 360 dis/min
Sb!5, 4,000 dis/min Ru’, 2,000 dis/min Zr®$, 800 dis/min Mn** and 650 dis/min Zn*5 per gram
wet weight as of 1 June 1957. Although pre-Redwingactivity still predominates, fission products
originating during Redwing had penetrated to the 1,000-fathom bottom southeast of Eniwetok Atoll
by December 1956.
5.6.6 Radioactive Contamination of Marine Organisms. The predominant radioisotopes found
in the marine organisms of the EPG, both prior to and during the Redwing testing, were not fisSion products, but instead were isotopes of the transition elements, cobalt, zinc, and manganese.
In April 1956, the pattern of contamination exhibited chiefly Co5™ and Co® in the molluscs, Zn‘
in the surface fish and Ce!*4 and Ru!®* in the phytoplankton.
117
Zooplankton collected in the open sea