Title: IRON-55 IN PACIFIC OCEAN ORGANISMS Abstract approved:

Large quantities of 55Fe, formed by nuclear testing during 1961 and 1962, have been deposited on the North Pacific Ocean as fallout and concentrated by marine organisms. As a result of this high 55Fe fallout and of low concentrations of iron in the ocean, marine organisms are the site of high 55Fe specific activity (55Fe activity/weight of total iron). Iron-55 specific activity was seen to vary among five species of Pacific salmon, with sockeye salmon showing highest and chinook salmon showing lowest 55Fe specific activity. Variation of 55Fe specific activity among species of salmon appears to result from their migration routes and feeding habits. In 1964 at Strait of Juan de Fuca, Canada, where the largest 55Fe specific activity difference between the chinook and sockeye salmon was observed, the 55Fe specific activity of chinook salmon was 0. 745 Ci/g Fe and that of Redacted for Privac