34 



REDFIELD, KETCHUM AND RICHARDS 



[CHAP. 2 



the AOjAP ratio. The difference between this quantity and the total quantity 

 of nutrient present in inorganic form gives the quantity of preformed nutrient 

 present. In estimating the fraction of oxidative origin, it is convenient to note 

 that a JO/JP ratio of — 276 corresponds closely to the production of 1 mg 

 atom/m 3 of phosphorus in the consumption of 3 ml Oo 1. 



The distribution of these fractions of inorganic phosphorus at two stations 

 in the North Atlantic is shown in Fig. 4. At the station in the subtropics (a) 



2.0 



P (mg otoms/m 3 ) 



Fig. 4. Fractions of total phosphorus, Pj, present as phosphorus of oxidative origin, P ox , 

 and as preformed phosphorus, P p , at stations in North Atlantic. 



(a) Crawford Station 364; 16° 16'N, 54° 44'W. 



(b) Discovert/ Station 3849; 55° 25'N, 33° 12'W. 



more than half the phosphorus in the deep water is preformed and this fraction 

 is present in practically the same concentration at all depths below 700 m. 

 Above this depth the preformed phosphorus diminishes and is absent in the 

 layers immediately below the surface. At the station in high latitude (b) about 

 three-quarters of the total phosphorus is present in the preformed fraction and 

 it is only in the surface layer that its concentration is reduced by assimilation 

 by the phytoplankton. 



As defined, the preformed nutrient concentration is a conservative property, 

 being uninfluenced by the oxidation of organic matter which was present in 

 the water mass at the time of its sinking or which has accumulated in the water 

 at depth. Its value depends on the degree to which conditions at the sea surface 

 influence the synthetic processes at the time the water masses are formed. In 

 contrast, the apparent oxygen utilization, or its equivalent in nutrient, provides 

 a measure of the effect of biological activity on the composition of the water 

 since it sank below the influence of the atmosphere. 



The validity of the concept of preformed nutrients and the method of their 

 estimation may be tested by examining the values in water masses which may 



