Chapter 5 



THE EFFECTS OF THE ECOLOGICAL SYSTEM ON THE TRANSPORT OF 



ELEMENTS IN THE SEA ' 



BOSTWICK H. Ketchum, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 



Some elements may be profoundly influenced 

 by the biological cycle and their resulting dis- 

 tribution in the sea may be quite different from 

 the distribution of elements that are affected 

 only by the circulation of the water. Numer- 

 ous examples of the modification of distribution 

 by biological activities could be given but it 

 may suffice to review briefly the vertical distri- 

 bution of phosphorus in the ocean. 



The photosynthetic fixation of carbon is lim- 

 ited to the surface hundred meters or less of 

 the sea by the penetration of light, and the 

 plant nutrients, including phosphorus, are as- 

 similated there. The surface concentration of 

 these elements may be reduced to virtually 

 zero. Below the photosynthetic zone, the con- 

 centrations of these nutrients increase, reaching 

 maximum values at depths of 200 to 1000 

 meters, the actual depth depending upon loca- 

 tion and the oceanic circulation. These maxi- 

 mum concentrations are produced by two proc- 

 esses. The water at intermediate depths is 

 formed by cooling at high latitudes in the 

 ocean, where it sinks and spreads out. At the 

 time of sinking, it contains some inorganic 

 phosphorus and organic matter which is de- 

 composed, liberating the plant nutrients and 

 decreasing the oxygen content. Additions to 

 the organic matter from the surface waters 

 occur everywhere, increasing the nutrient maxi- 

 mum concentration and decreasing the oxygen 

 minimum. Below the nutrient maximum-oxygen 

 minimum layer the concentration of phosphorus 

 decreases again reaching values which are gen- 

 erally constant and uniform from a depth of 

 about 1500 meters to the bottom (Redfield, 

 1942). 



The general patterns of distribution of the 

 elements important in plankton growth on an 

 ocean-wide scale are thus quite different from 



1 Contribution No. 871 from the Woods Hole 

 Oceanographic Institution. 



the pattern of distribution of the major ele- 

 ments. The processes which must be considered 

 in order to evaluate biological effects on the 

 ultimate distribution of radioisotope wastes or 

 contaminants in the sea include (1) the assimi- 

 lation or adsorption of the elements by the bio- 

 logical populations, (2) the effects of gravity, 

 (3) vertical migrations, (4) horizontal migra- 

 tions, and (5) the effects of stationary popula- 

 tions in flowing systems. 



It has been shown in another section of this 

 report that biological populations may concen- 

 trate by several orders of magnitude various 

 elements and their radioisotopes. To evaluate 

 the possible significance of this in the oceans, it 

 is necessary to determine the quantity of living 

 material present (the biomass) and the rate of 

 production of the populations of the ecological 

 system. The biomass, when combined with the 

 known concentration factor, will indicate how 

 much of an element in the water may be com- 

 bined in the living organisms. The most active 

 concentration of elements may occur during the 

 rapid growth of populations; consequently it 

 is also essential to know the rate of production 

 of the various populations involved. A few data 

 on both the biomass and the rate of production 

 of various populations in the sea are given in 

 Tables 1 and 2. 



The biomass figures indicate that concentra- 

 tion factors of 12,500 or more would be re- 

 quired, under static conditions, to incorporate 

 half of an element in a cubic meter of water 

 within the ecological system even in the high 

 concentrations of living material found in red- 

 tide blooms. However, the biological popula- 

 tions are not static; those movements which are 

 independent of the motion of the water can, 

 by repetition, transport larger proportions of 

 elements than is indicated by static equilibrium 

 conditions. The productivity values in Table 2 

 indicate that several times the standing crop 

 of phytoplankton is produced annually. Both 



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