during a particular period may be carried thousands of miles by the ocean currents in a year. In addition, the processes of precipitation and scavenging going on in the ocean tend to distribute individual isotopes quite differently than those found on land. A portion of the deposited activity will precipitate and settle to the ocean bottom, whereit is relatively unavailable. Other material may be concentrated by marine organisms and may appear at relatively high levels in the food chain. It is of interest, however, to attempt to develop a picture of the distribution of the radioactive isotopes in the sea, both geographically and as a function of depth. A large proportion of the measurements made have indicated levels such that very large samples are required for radiochemical analysis for individual isotopes. Therefore the results of most of the work have been reported in terms of mixed fission product activity. These data, like other mixed fission product analyses, are extremely difficult to interpret in themselves. Their value lies in indicating areas of higher activity and thus for possible sampling locations for Sr® or Cs!%? analysis. Early radiochemical data from the University of Chicago and from the Lamont Geological Observatory are reported in Table 20. More recent data developed by Dr. Vaughan T. Bowen of the Woods Hole Oceanographic Institution and Dr. Thomas Sugihara of Clark University are shown in Table 21. The Clark University group is continuing investigations of geographic and depth distribution in the Atlantic Ocean. Through the cooperation of the U. S. Navy, samples of surface sea water were collected in the Pacific from July 1956 into early 1958. Samples are taken during normal transport operations at about 100-mile intervals on several of the routes in the western Pacific. One-liter samples are obtained, and these are analyzed for mixed fission productactivity only. During the collection period well over 1000 of these samples were analyzed. The indi- vidual data are not tabulated since mixed fission product activities are not directly convertible to strontium or other single isotopes; however, a list of the cruises and the maximum activity obtained on each is presented in Table 22. 49