32 REDFIELD, KETCHUM AND RICHARDS [CHAP. 2 



each point represents the concentrations of a pair of elements determined from 

 a single sample of sea-water collected at varying depth in the western North 

 Atlantic. In general the low values represent samples from small depths and 

 the high values from greater depths. The slope of the line drawn through the 

 points gives the ratio of the difference in concentration of the elements in 

 question. These differences are assumed to be due to differences in the quantities 

 of organic matter of uniform composition which have decomposed in the 

 different samples. The ratios may be combined to give the relative proportions 

 of the several elements in question in the decomposed material. 



Table III gives these ratios as determined from the analysis of sea-water and 

 from analyses of plankton collections. The agreement so far as phosphorus, 

 nitrogen and carbon are concerned leaves little doubt that the changes in 

 concentration at depth arise mainly from the decomposition of plankton and 

 that the ratios are sufficiently precise to be useful in the analysis of oceano- 

 graphic problems. Similar treatment of data from the Pacific, Indian and South 

 Atlantic Oceans and the Barents Sea shows that the ratio ZlN/zJP = 15 applies 

 in sea-water on a world-wide scale. 



Table III 



Ratios of the Elements Involved in the Oxidation of Organic Matter in Sea- 

 Water at Depth and Those Present in Plankton of Average Composition, by 

 Atoms (after Richards and Vaccaro, 1956) 



a Corrected for salt error after Cooper (1938). 



b Estimated assuming 2 atoms Ool atom C and 4 atoms 0=01 atom N. 



It should be emphasized that these ratios do not represent the proportions 

 in which the elements are available in sea-water, but rather the ratios of change 

 in their concentration which result from biological activity. 



a. The oxidative ratio 



The relation of the change in concentration of oxygen in sea-water, shown in 

 Table III, to that of the nutrient elements does not agree well with the expecta- 

 tion raised by the statistical composition of plankton. This discrepancy requires 

 examination. 



Oxygen and carbon dioxide are exchanged with the atmosphere when sea- 

 water is at the surface and their concentrations in water sinking to depth is 



