54 



Atomic Radiation and Oceanography and Fisheries 



measured in terms of seasons or years. A com- 

 paratively small population of phytoplankton 

 doubling rapidly can provide the energy and 

 nutrients of an equivalent or even larger animal 

 population which is increasing more slowly. 



The size of various populations and their 

 rate of production in the English Channel has 

 been evaluated by Harvey (1950) and his re- 

 sults are given in Table 3. These illustrate the 

 above conclusions, since the average biomass of 

 animals exceed that of the plants, but the rate 



TABLE 3 Average Quantity, Throughout the 



Year, of Plants and Animals Below Unit 



Area of Sea Surface in the English 



Channel i 



Dry wt of organic matter 



Standing crop Production 



Organism g-/m^ g./mVday 



Phytoplankton 4.00 0.4-0.5 



Zooplankton 1.50 0.1500 



Pelagic Fish 1.80 0.0016 2 



Bacteria 0.04 — 



Demersal Fish 1.25 0.0010 



Bottom Fauna 17.00 0.0300 ^ 



Bottom Bacteria 0.10 — 



1 From Harvey (1950), depth equals 70 meters. 



2 Based on estimated mortality of 30 per cent per 

 annum. 



3 Based on estimated mortality of 60 per cent per 

 annum. 



of production of the plants exceeds that of the 

 animal populations. 



The plankton organisms in the open sea pro- 

 vide by far the largest quantity of living ma- 

 terial and by even more the largest organic 

 absorptive surface. Those radioisotopes which 

 are adsorbed will become bound to the organ- 

 isms, and they are as subject to the effects of 

 gravitation and migration as if they had been 

 assimilated and utilized. 



Gravity affects the organisms in a population 

 and can thus modify the distribution of ele- 

 ments which become incorporated in the bio- 

 logical cycle. Ultimately only two fates await 

 most of the plankton which grows in the sur- 

 face layers. It may be eaten by the herbivores 

 or it may sink out of the illuminated zone and 

 decompose at greater depths. If the plankton 

 is eaten by a herbivore, a proportion of the 

 organic matter is incorporated into the herbivore 

 body but an even larger proportion is returned 

 to the water as excretion or faecal pellets. The 

 excretions may be present in the water inhabited 



by the plankton and reused in situ. The faecal 

 pellets settle into the deeper water where they 

 decompose. Gravity thus imposes on elements 

 which become incorporated in the biological 

 system a modification of the distribution which 

 would be produced by movements of the water 

 alone, since they tend to accumulate at some 

 intermediate depth in the water column, or on 

 the bottom. 



One of the unsolved problems of marine 

 biology is the definition of the proportion of 

 organic matter which is decomposed by the time 

 the particulate material sinks to various depths. 

 This problem must be solved before an evalua- 

 tion of the biological effects on the distribution 

 of radioisotope contamination of the seas can 

 be made. It may be worthwhile to summarize 

 some of the present thinking on this problem. 



In the first place, everywhere that samples 

 have been taken in the deep sea, living organ- 

 isms have been found. Since we know of no 

 mechanism other than photosynthesis at the sur- 

 face which can provide the organic material 

 necessary to support these populations, it is 

 clear that some of the surface produced material 

 must reach all depths of the ocean. It may be 

 argued by some that the bacterial chemosyn- 

 thetic processes are a source of fixed carbon 

 which has not been considered, but the condi- 

 tions in the deep sea are not suitable for the 

 formation of organic matter by any of these 

 processes. 



The presence of the nutrient maximum-oxy- 

 gen minimum layer at intermediate depths in 

 the sea has led to the conclusion that most of 

 the organic matter formed at the surface must 

 be oxidized by the time it has sunk to a depth 

 of 1000 meters (Redfield, 1942). Analyses of 

 organic phosphorus in the equatorial Atlantic 

 Ocean showed considerable amounts in the 

 waters above 1000 meters, but none at greater 

 depths (Ketchum, Corwin, and Keen, 1955). 

 There is no present evaluation of the quantity 

 of organic carbon which can sink to greater 

 depths, nor is it possible to evaluate whether 

 this quantity would be sufficient to support the 

 known populations of archibenthic organisms. 

 These two extremes thus define the dilemma. 

 Namely that some organic matter must reach 

 the great depths, but, at the same time, most of 

 the decomposition appears to occur above a 

 depth of 1000 meters. 



The secular change of oxygen in the deep 



