Research Projects
The AEC supports oceanographic research conducted by its own laboratories and by other federal agencies, as well as by non-government research scientists. The Environmental Sciences Branch of the Division of Biology and Medicine has begun the long and complex task of unraveling the mystery of the fate of radionuclides in the ocean. Valuable techniques have been developed for the intentional injection of radioisotopes into the sea for specific research. Scientists are now able to conduct investigations that were never before possible. In some instances, traditional scientific concepts and theories have been shattered, or at least severely shaken, by new evidence gathered by radioisotope techniques.
Since 70% of the earth’s surface is water, at least 70% of the radioactive debris lofted into the stratosphere during atmospheric nuclear weapons tests falls into the ocean. An additional small proportion finds its way into the sea as the run-off from the land. In the case of tests at sea, the majority of radiation immediately falls into the water nearby. For this reason, the ocean around the sites in the Marshall Islands where U. S. tests were conducted has provided a unique opportunity to study the effect of large concentrations of radionuclides. Particularly significant studies have been conducted of the absorption of radionuclides by plants and animals living on nearby reefs and islands, and of both lateral and vertical diffusion rates of elements in the open ocean.[8]
The 1954 nuclear test at Eniwetok Atoll produced heavier-than-expected local radioactive fallout. Since then, both American and Japanese scientists have studied water-mass movement rates, using the fallout radionuclides strontium-90 and cesium-137 themselves as tracer elements. These nuclides produced in the test have been detected at depths down to 7000 meters in the far northwestern Pacific in the vicinity of Japan.
Autoradiograph of a plankton sample collected from a Pacific lagoon a week after a 1952 nuclear test, showing concentration of radioisotopes (bright areas).
If this results from simple eddy diffusion, as some scientists believe, it is a case of diffusion at a very high rate. Other scientists suggest that other factors may have contributed to the vertical transport of the radionuclides to these depths. Still others believe that the strontium-90 and cesium-137 might not have originated with the U. S. Pacific tests at all, but rather with Russian tests in the Arctic taking place at about the same time. They propose the theory that a syphoning effect in the Bering Strait causes a current to flow out of the Arctic Ocean and down under the surface waters of the western Pacific. In support of this, Japanese researchers cite a dissolved oxygen content where these measurements were made that is different from that of other deep water in the area. If this theory should be proved correct, it would be the first indication that such a current exists.
Similar investigations have been conducted of the variations in depth of strontium-90 concentration in the Atlantic Ocean. In February 1962, when fallout from 1961 nuclear tests was high, tests south of Greenland showed that mixing of fallout was fairly rapid through the top 800 meters of water. At greater depths a colder, saltier layer of water contained only about half as much strontium-90, confirming other evidence that interchange between water masses of different physical and chemical properties is comparatively low.
Work such as this has emphasized the difficulty in making meaningful measurements of man-made radiation in the ocean. One problem is to separate the artificially produced radiation from the natural radiation, namely that from potassium-40 (which accounts for 97% of oceanic radiation) and from the radionuclides, such as tritium, carbon-14, beryllium-7, beryllium-10, aluminum-26, and silicon-32, created in the stratosphere naturally by cosmic-ray bombardment.
