os e oF ray "eo PREFACE Much time has passed since the Castle Operation when the effects of fallout upon the open sea were first studied by oceanographic methods. More recent field tests have contributed fay more data concerning the radioactive contamination of marine organisms than could be collected during the hastily outfitted cruise of the U.S.S. SIOUX following Castle, Shot5. Nevertheless the two small samples of plankton that were collected by the SIOUX were sufficiently impressive to influence the thinking of people making preparations for later operations, and, in particular, the thinking of people involved in the problem of oceanic disposal of atomic wastes. Today these specimens themselves do not appear so spectacular, nor have some of the hypotheses that guided their analyses been completely substantiated. It is now common knowledge that marine organisms are notorious concentrators of radioactive debris from nuclear detonation; and biologists, radiochemists and oceanographers have acquired enough interest and experience to carry out we -l~organized and integrated research on the problems. For these reasons the original interim report has been re~ written and some of the conclusions have been left out. Critical original experimental data from field expeditions retains its value almost indefinitely, however, and this paper reports the first direct in situ evidences of the profound influence of deep sea organisms on the partition of radioactive debris from atomic weapons, and directly demonstrateg the inadequacy of a model that accommodates only the physical processes of mixing, advection, etc. This fact justifies a final report. The authors wish to point out that proper credit has not yet been directed to certain people who were largely responsible for the original conception of the expedition and outfitting of it so thet it could be successful. It was Professor John D. Isaacs who, in fact, proposed that plankton samples be taken and wna located and acquired the special net that was needed, as well as the other oceanographic gear, and it waa to a great degree the scientific and administrative experience of Professor Isaacs and of Dr. Edwerd Martell that pulled the project together as an operational unit. It is almost impossible to be sure that proper credit is givea tu everyone who con~ tributed to this special aspect of the Castle project. The radioanalyses of Table 2 ware done at NRDL by Doctors R.W. Rinehart, J.A. Seiler, W.H. Shipman, and others and the data transmitted to SIO by Dr. L.B. Werner with valuable comments. Dr. Edward D. Goldberg was responsible for the beta and gamma measurements shown on Table 1 and Figures 1, 2, and 3; the beta analyses were carried out at SIO but the gamma spectra were measured at NRDL. ‘ Dr. Martell reviewed the preliminary report and demonstrated that these early, scanty, experimental findings could hardly justify the conclusiona expressed. The authors con= curred and the report has been revised extensively.