>, and to eddyeffect, if this exists. currents of radioactivity in the Suciura and Kamepa (6), by er the nuclear tests at Eniwetok to a distance of 1,200 miles, which - day. Harley reported the west- miles west from Bikini, which Marsh approximately six weeks Test Site (Seymour ef al.), the lerived from a surface detonation Marsh survey, the centre of this ini Atoll. During the intervening of 300 miles at an average rate of tive material in this area of high the surface waters (above 25 m), aminated water from the original direction of the prevailing winds adioactivity was carried by the id and remained in the surface rinal contaminated deeper waters fairly large size and scavenge the accompanying radioisotopes out of the mixed layer and through the thermocline into the deeper layers. Plankton undergoes diurnal vertical migrations of distances that exceed the depth of the thermocline, and thus may carry with it radioelements adsorbed or ingested in the mixed layer. Thus three layers of water in the ocean are normally present—the surface te etok Test Site the westward drift ial to that of the current speed, is may be attributed to the effect kton into deeper water, where the laver or mixed layer, in which mixing should occur easily; the thermocline, which is very stable and across which radioisotopes may exhibit appreciable movement only under special conditions; and the body of water below the thermocline, in which vertical mixing is limited. REVELLE, FoLtsom, GOLDBERG and Isaacs (8) (1955) reported that when fission products were introduced at the surface of an area where the mixed layer was approximately 300 feet thick, the radioactivity moved down at a rate of about 11 feet per hour, so that within 28 hours the radioactivity was uniformly distributed to the thermocline. Any study concerning the influence of gravity on radioactive materials in the open sea is complicated by the effects of currents and turbulent diffusion. If the leading edge of the contaminated body of water is sampled with passage MIXED lmost due west, and according to vity in comparison with the surhave initially contained apprecine of the second survey had sunk 220 he rate of vertical diffusion that of molecular diffusion and dispersion. The extent of vertical he surface winds and the vertical 180 + LAYER — 28HOURS 693,740 476,000 600,000 184,000 PARTIC- 166,800 ULATE 93740 111,500 13.5 37.7 d/m d/m SOLUBLE ‘PLUS COLLOIO dm 200 300 m). 6 HOURS H 642,800 TOTAL > > 160 5 > 5140 F- PARTIC ULATE 26.0 46 HOURS 295,500 < rature change and separates the tok Test Site is Jess than 100 m temperature is fairly consistent in this layer should occur easily cause the thermocline is a layer this layer by turbulent diffusion wn in the upper layer. Therefore 1ermocline should remain in the to great horizontal distribution However, radioactive materials methods: ied by large amounts of stable 8 where weapons are fired over lay precipitate into particles of 9 2 120+ « 100 F 80F 6 HOURS —-~- 28 HOURS cot vow48 HOURS 40 et 20 l o 1 625050 Teese “20077 MO eceescassneeeree wt 75s«éd1000 OEPTH 1 i 150 200 IN 300 METERS Fig. 1 Distribution of total radioactivity in sea-water with depth at 6, 28 and 48 hours 109