General Considerations 



21 



some evidence, however, from carbon 14 meas- 

 urements made by the Lamont Geological Ob- 

 servatory that in fact fairly complete mixing 

 occurs within the deep sea during the average 

 residence time of a water particle. 



Another calculation, based on very conserva- 

 tive assumptions concerning the mixing proc- 

 esses, was made in the report of a meeting of 

 scientists from the U.S. and U.K. (Anon., 

 1956). It was assumed that fission products 

 deposited on the ocean floor in mid-latitudes 

 would drift and disperse for at least 10 years 

 before surfacing, at which time the contami- 

 nated area would be a disc about 2 km. thick 

 and 70 km. in diameter, which would be sub- 

 sequently dispersed throughout the surface layer. 

 Repeated deposits of 1 megacurie of Sr 90 (0.4 

 tons of mixed fission products) made at the rate 

 of ten per year would result in an average con- 

 centration of Sr 90 of not over 10'^ microcuries 

 per liter in the mixed layer, or .025 microcuries 

 per kilogram of calcium. 



Although we cannot say at this time with any 

 precision what quantities of reactor-waste prod- 

 ucts can be safely deposited in the deep sea, it 

 appears certainly safe to employ quantities up to 

 a few tons a year in careful experimental studies. 

 It is not impossible that 1,000 tons a year can 

 be safely disposed of in deep, isolated basins 

 where the residence time is much greater than 

 the 300-year average estimated for the deep sea 

 generally. For quantities of the order of 100 

 tons a year or more, effects on the animal popu- 

 lations of the deep sea, and resulting effects on 

 the whole ecology of the sea could become im- 

 portant; as to this no information is at present 

 available. 



VIII. What We Need to Know 



Our knowledge of most of the processes in 

 the oceans is altogether too fragmentary to per- 

 mit precise predictions of the results of the in- 

 troduction of a given quantity of radioactive 

 materials at any particular place. In order to 

 obtain the necessary knowledge, an adequate, 

 long-range program of research on the physics, 

 chemistry, and geology of the sea, and on the 

 biology and ecology of its contained organisms 

 is required. Such research must be directed 

 toward the understanding of general principles, 

 not simply to the ad hoc solution of a particu- 

 lar local problem for immediate application. 

 The latter sort of study is, of course, desirable 



in order to provide engineering solutions to par- 

 ticular waste-disposal problems as they arise. 

 Such engineering solutions must necessarily be 

 of limited application and, moreover, they must 

 always be conservative, at least until sufficient 

 broad understanding is obtained. 



MAJOR UNSOLVED PROBLEMS 



Some of the major basic problems that should 

 be included in the research program can be 

 briefly outlined: 



1 . Dispersion in the upper mixed layer 



Fairly extensive information is available on 

 the mean velocities and transport of the major 

 surface currents. The transient currents and 

 eddies that result in dispersion in both the hori- 

 zontal and vertical directions are, on the con- 

 trary, not understood. Some empirical param- 

 eters approximately describing the relationships 

 of diffusivity to time and to size of area have 

 been developed, but understanding of the de- 

 tailed physical principles is lacking. In con- 

 sequence, it is not possible to predict on the 

 basis of more elementary properties the disper- 

 sion of materials introduced into the upper layer 

 at a given point. Direct measurements must be 

 made, and these are costly and not necessarily 

 reliable. Basic research on the turbulent motion 

 of water in the upper layer is needed. 



2. Circulation in the intermediate and deep 

 layers 



For the region of the sea below the surface 

 layer, we not only do not understand the nature 

 of the turbulent motion, we do not even have 

 a description of the mean currents. The chart- 

 ing of the deep currents, and investigations 

 toward elucidating the physical principles in- 

 volved should be vigorously pursued. 



3. Exchange between the surface layer and 

 deeper layers 



It is important to determine the average rate 

 of exchange of water between the surface and 

 the deep layers, as a basis of estimating average 

 "hold up" times of dissolved materials deposited 

 in the deep layer. It is probably even more im- 

 portant to measure the heterogeneity in the ex- 

 change system, that is to measure the rates of 

 exchange in different areas and depths. We 



