SECT. 1] THE INFLUENCE OF ORGANISMS ON THE COMPOSITION OF SEA-WATER 



39 



estimated the oxidative ratios for ocean water and has found them to vary 

 substantially at different depths (see page 68). His investigations throw doubt 

 on the strict application of the statistical composition of the plankton to 

 estimations of the oxidative ratios of nitrogen and phosphorus at different 

 depths in the sea. 



C. The Availability of Nutrient Elements in Sea-Water 



In considering the chemical changes in sea-water produced by organic 

 activity it is convenient to establish a norm from which variation in concentra- 

 tion can be measured. Table V has been prepared for this purpose. The norm 

 for phosphorus is based on conditions observed in the deeper water of the 

 Southern Ocean. Nitrogen is derived from this value employing the ratio of 

 15:1 proposed by Cooper (1937, 1938a) as a normal ratio from which anomalies 

 may be measured. The carbon concentration is the value given by Sverdrup, 

 Johnson and Fleming (1942) for water of 19% chlorinity and the oxj^gen 

 saturation value corresponds to water of this chlorinity in equilibrium with 

 the atmosphere at 2°C. Table V shows the ratios in which these elements are 

 available in "average'' sea-water and in which they are utilized by plankton 

 in forming organic matter, and also the ratio of availability to utilization. A 

 number of interesting generalizations may be developed from these estimates. 



a. Limiting factors 



Liebig's law of the minimum implies that in the growth of a crop of plants, 

 when other factors such as light and temperature are favorable, the nutrient 

 available in smallest quantity relative to the requirement of the plant will 

 limit the crop. The ratios presented in Table V define concretely the relation of 

 availability of the several elements present in sea-water to their utilization. 

 Nitrogen and phosphorus appear to occur in sea-water in just the proportions 

 in which they are utilized by the plankton, a fact first noted by Harvey (1926) 



Table V 



Availability of Nutrient Elements in "Average" Sea- Water (5 = 34.7%,,, 

 T = 2°C) and the Ratios of Their Availability and Utilization by Plankton 



Availability in 

 "average" sea- 

 water 



A , 



mg atoms /m 3 ratio 



Phosphorus 

 Nitrogen 

 Carbon 



Oxygen saturation 

 value 



2.3 

 34.5 

 2340 

 73r> 



1 



15 



1017 



320 



Utilization 



by 



plankton 

 ratio 



1 



16 



106 



276 



Ratio of 

 availability 



to 

 utilization 



1 



0.94 



9.6 



1.16 



