FALLOUT IN THE OCEAN INTRODUCTION The following discussion of fallout in the oceans is, the most part, a discussion of local, for not stratospheric fallout. Local fallout is defined as the fallout that occurs during the first day or two following the detonation of a nuclear device and within a few hundred miles of ground zero. Local fallout differs from stratospheric fallout in several important aspects. In an area of local fallout the amount of fallout per unit area and the size of the fallout particles are considerably greater than in an area of stratospheric fallout only. Fora surface explosion 65 to 85 per cent of the fallout may be local and for an underwater detonation local fallout may be even greater. Also, the chemical form and the percentage composition of the radioisotopes in the two areas may differ. For the megaton weapons fired in the Pacific the bulk of the fallout resides on particles of CaO or Ca(OH)2 or mixtures of Cao, caCO3z Ca (OH) 9 and made by the great heat of the fireball acting on the coral of the islands and sea floor. A large amount also is carried on NaCl particles The large particles of these com- (Libby, 1956). pounds fall out locally and do not enter the stratosphere. a consequence greater quantities and different species of As