136 



Atomic Radiation and Oceanography and Fisheries 



ganisms under study being in it over a known 

 period of time, and (2) have a sufficiently high 

 radioactivity that it may be followed from ship- 

 board. If we use only fission products which 

 organisms concentrate; then, since longer count- 

 ing periods are feasible for samples of the 

 organisms than are feasible for the equipment 

 used to locate and follow the water mass, the 

 radioactivity required to determine the position 

 of the contaminated water mass is expected to 

 be the limiting factor in the experiment. 



Revelle, Folsom, Goldberg and Isaacs (1955) 

 have indicated that, in the slow-mixing levels 

 of the sea below the thermocline, vertical mix- 

 ing is almost negligible, so it may be expected 

 that while the area in which the isotopes can 

 be detected spreads over a radius of 4.1 km., 

 vertically it will be limited to about 1 meter. 

 In these circumstances, it has been calculated 

 that 10 curies of gamma emitter may be detected 

 until it has spread laterally to a radius of 4 km., 

 or a mean concentration of about 2x10"^ curies 

 per cubic meter. They do not specify the time 

 involved, but it may be presumed to be of the 

 order of one week to one month. For biological 

 experiments, it would be necessary to make 

 observations over a longer period of time, also 

 we cannot commence significant biological ob- 

 servations until the contaminated area is suffi- 

 ciently large to ensure knowledge of which 

 animals are or have been in the active water. 

 For these reasons the time involved should 

 perhaps be increased by a factor of 10. If the 

 diffusion of the contaminated water, both ver- 

 tically and horizontally follows the "random 

 walk" law, the volume containing the activity 

 will increase linearly with time, and, in conse- 

 quence, about 100 curies of gamma activity will 

 be required. 



Experiments in the upper mixed layer will 

 require much larger quantities of fission prod- 

 ucts. Mixing to the top of the thermocline is 

 very rapid; according to the authors above 

 cited the lower boundary of radioactive water 

 moves down at about 10'^ cm/second. If we 

 select an area, such as that off Central America 

 where there is a fairly shallow sharp thermo- 

 cline at a mean depth of about 20 meters, mix- 

 ing down to the top of the thermocline would 

 be complete in less than ten hours. Thereafter 

 downward mixing should be negligible. Recent 

 experiments suggest that the radius over which 

 the water spreads laterally is increased as about 

 the 0.8 power of time. In Bikini lagoon it has 



been found that the radius of the radioactive 

 area increased to 4 kilometers in 3 days. If 

 we ran an experiment for 90 days, which is 

 probably the time necessary to follow the flux 

 of radioelements through two or more trophic 

 levels, we would, then, expect the radius to 

 approximate 



r= 4 (30) -8=: 60 kilometers. 



The volume would then be (with a 20 meter 

 thermocline) 



77X36x10^x20 cubic meters 

 or about 225 X 10^ cubic meters 



To be still detectible at this dilution, using the 

 above estimate of 2 x 10""^ curies/cubic meter, 

 an initial quantity of some 4x10* curies would 

 be required. The logistics of handling large 

 quantities of fission products will be difficult, 

 but not perhaps impossible. 



Because of the smaller volume of water to 

 be dealt with, it may be most desirable, at least 

 initially, to conduct such experiments in a small 

 enclosed arm of the sea. Such an environment 

 is diflferent in many respects from the open 

 ocean, but much useful information about fluxes 

 of radioelements through the several trophic 

 levels could be obtained. It would not be diffi- 

 cult to select a small bay, with a narrow, shal- 

 low entrance, which could be cut off temporarily 

 from the sea for this purpose. A body of, say, 

 one square kilometer with an average depth of 

 ten meters might be used, giving a volume of 

 lO'' cubic meters. Since the problem of locating 

 the water mass is eliminated, and fairly large 

 volumes of water can be filtered for organisms, 

 rather small quantities of fission products, which 

 would not be hazardous, could be employed. 

 One curie would be ample, and the contamina- 

 tion of the water itself would be within safe 

 levels for human hazards. 



It was noted earlier that one of the important 

 fundamental ecological problems is to measure 

 the flux of carbon through different trophic 

 levels. Since the fraction of the carbon taken 

 up by plants is a very small part of the total in 

 the sea water, experiments with radio-carbon in 

 the open sea are not feasible. Experiments 

 using samples in bottles have been conducted 

 in situ in recent years, but these have two de- 

 ficiencies: (1) the surface and other effects of 

 the container modify the environment so that 

 the resulting computations for photosynthesis 

 probably are not those that would have occurred 



