38 REDFIELD, KETCHUM AND RICHARDS [CHAP. 2 



first inorganic product in the regeneration of nitrate. In shallow coastal waters 

 in temperate regions it is present in very small quantities at the end of winter, 

 but increases as the season advances, and may become the principal form in 

 which nitrogen is available in the water (Cooper, 1933). Under such conditions 

 it may be absorbed directly by the phytoplankton without being oxidized to 

 nitrite and nitrate (Harris, 1959). During the autumn and winter the ammonia 

 decreases and nitrate becomes the major fraction of inorganic nitrogen in the 

 water. In the deeper water of the Gulf of Maine ammonia appears in spring 

 immediately below the photosynthetic zone and increases during the summer 

 to occupy the entire water column (Redfield and Keys, 1938). In the deep sea 

 ammonia does not ordinarily occur in significant quantities below the photo - 

 synthetic zone, except in anoxic basins. 



Nitrite appears to be more evanescent than ammonia. Both fractions tend 

 to accumulate below the euphotic zone where regeneration may be assumed 

 to be intense. Under these conditions its concentration is much smaller than 

 that of ammonia. In oceanic waters a second zone of increased nitrite con- 

 centration may be found at greater depths if oxygen is greatly reduced. This 

 accumulation is attributed by Brandhorst (1959) to the reduction of nitrate by 

 denitrifying bacteria. 



Ammonia and nitrite are intermediate products of the nitrogen cycle which 

 are present where organic matter is decomposing in quantity. In the deep sea 

 where the increment of organic matter is small, relative to the rate of renewal 

 of the water, the regeneration process runs nearly to completion and inorganic 

 nitrogen is present almost entirely in the form of nitrate. Consequently, these 

 intermediate products may frequently be neglected in examining the influence 

 of organic activity on the chemistry of the deeper ocean waters. 



There is some evidence that the regeneration of nitrate occurs more slowly 

 than that of phosphate in shallow waters. This has been explained by the time 

 required for bacteria to complete the several stages leading to the formation 

 of nitrate (Atkins, 1926). It has also been observed that the maximum con- 

 centration of nitrate in the nutrient-rich layers of the ocean occurs at a greater 

 depth than does that of phosphorus. This fact has been attributed to the more 

 rapid release of phosphorus from the plankton as it sinks. The matter is of 

 interest in the present connection since it provides a mechanism by which 

 nitrogen and phosphorus may be fractionated and thus may explain the 

 variations in the ratios of these elements in sea-water. 



Frequently the minimum concentration of oxygen at stations in the deep 

 ocean does not coincide in depth with that of the maximum concentration of 

 phosphorus or nitrogen. Such deviations may arise because of the presence 

 of preformed nutrients in the water or because the initial oxygen content of 

 the water at different depths has been different owing to its temperature at 

 the time when it sank below the surface. It is only when such influences have 

 been eliminated that departures may be interpreted as indicating differences 

 in the composition of the organic materials being oxidized at different depths. 

 Using procedures to which this stricture does not apply, Riley (1951) has 



