. 14 activity extending from Bikini to Eniwetok and continuing west- ward to the southwest corner of the sampling area. The highest levels along this line were greater than 50,000 c/m/g in the area from Eniwetok to about 35 miles westward. veyed, In the area sur- the lowest values were in the northwest quadrant, with the minimum value, 1,300 d/m/g, at the most northwesterly sta- tion, 1A, at 14° N - 159° E. The plankton tows were made to a depth of about 200 meters, which assured complete sampling of the stirred layer. It is generally accepted that the stirred layer exists only above the thermocline, a region in which temperature decreases rapidly with increase in depth. Bathythermograph casts were made at each station to determine temperature changes with depth and from these data the area of the thermocline was determined. amples of bathythermograph traces are shown in Figure ll. ExSur- face temperatures were approximately 81° to 83°F and remained practically unchanged to a depth of about 300 feet; below 300 feet temperatures decreased, and at the 450 foot level were 70° to 74°F, indicating that, in general, the upper limit of the thermocline was just below 300 feet or about 100 meters. Water: The radioactive content of the water samples from the fifty-three collecting stations is presented in Table l. The sums of the values of radioactivity of the residue from one liter of sea water and of the filtered water, Station and depth are given in Table 2. less 40 for each Table 3 summarizes the percentage contribution of each component to the total radioactivity for all stations at each sample depth.