DRAFT es, contaminated water moves over relatively clean water and clean water flows in above the lower contatinated portion. Simultancous- ly, vertical turbulence acts to homogenize the ent#ts laycr above the thermocline, thereby diluting the contaminated water. ror fallout over a small area from a nominal kiloton weapon the primary mixing process is the latter effect discussed above, the vertical shear. ‘orizontal shear in the currents cver a sm4ull area is generally, although not always, rclative:y suall. California coast, measurements of herizontal disnersior ke U Cff the hy, The horizoutel molecular diffusion is eiso minor. vo both horizontal shear and aiffusion gave an averaze rate of ore foot per minute for areas up to 10 miles across. mee 7 ogee co * North In toe e ‘9 Equatorial Current region where current sreods ure stronger thon 4 6s off California, this rate woul probably be two or th:i-ea tines as great; nevertheless, tne effect cf the process would be of 2 second ordere For both small and large contaminated cesanic O oO n Eete Large, heavy part: roe areas the rates of vertical mixing are essentially equal. in the fallout (c.g., coral) must Sink fairly rapidly ana secount for rediocactivity found cn the Geep ocean bottom in the PPG. sut much of the Talloue redio- activity is on ssialler coral particles, or ash material and is dissolved into the water ebove the thernocline. Coral particles that are 100 microns in diam. ter would sink et the rate of 30 to 100 meters per hour; these would reach the thermocline in 2 or 3 ar hours time on the average and may lose much of their radiogectivity. Both the measurements made at CASTLE and by the Japanase one ww two months after C,STLE showed mach greater concentration of activity above the thermocline than anywhere else in the water column. aK