within a predictable depth interval as they often are in other regions. 

 The absence of such features helps to confirm the view that most 

 of the waters which have not been defined in this report can be considered 

 to be mixtures of the three primary water masses defined in Section IV. 



Figures 36 and 37 indicate that there were significant differences 

 in micronutrient relationships in the three primary water masses. 

 For a given reactive phosphorus concentration, reactive silicate 

 concentrations in the Arctic Bottom Water were usually considerably 

 higher than in Atlantic Water or Polar Water. This helps substantiate 

 the view that processes such as the ones mentioned above lead to 

 silicate enrichment of the deeper layers. In the three primary water 

 masses, the lowest micronutrient concentrations generally were found 

 in the Polar Water. This is not surprising, because, of the three, 

 Polar Water was generally found closest to the surface, and its micronutrient 

 levels probably had been reduced by phytoplankton activity. There 

 was a tendency for nitrate concentrations corresponding to a given 

 reactive phosphorus concentration to be much higher in Arctic Bottom 

 Water and Atlantic Water than in Polar Water. Even when nitrate 

 could not be detected, reactive phosphorus concentrations in the 

 Polar Water were fairly high («0.6 jug-at/liter) . Waters with high 

 reactive phosphorus/nitrate ratios have been found in the East Siberian 

 Sea and in Bering Strait, and undetectable concentrations of nitrate 

 coupled with reactive phosphorus concentrations of as much as 1.5 

 ;ug-at/liter have been encountered in East Siberian Sea surface waters 

 (Codispoti 1965). It is possible that the presence of appreciable 

 quantities of such waters could be responsible for the similar phenomena 

 noted in the Polar Water. However, other reasonable mechanisms could 

 be invoked to explain this condition, and more study is necessary 

 before its exact causes can be determined. 



- Figure 38 portrays a number of interesting features of the micronutrient 

 relationships in the upper 50 meters of the survey region. R.eactive 

 silicate and reactive phosphorus appeared to be present in sufficient 

 quantities to allow continued phytoplankton growth. Nitrate, on 

 the other hand, was often present in such low concentrations that, 

 in some localities, phytoplankton growth may have been limited by 

 the supply of biologically available nitrogen. Some of the reactive 

 phosphorus concentrations may appear to be low, but it must be remembered 

 that the average ratio in which phytoplankton utilize silicon, nitrogen, 

 and phosphorus appears to be approximately 22Si:16N:lP (Redfield, 

 Ketchum, and Richards 1963). At some stations, nitrate concentrations 

 in the surface layers appeared to be high enough to support continued 

 phytoplankton growth, indicating that in these areas other factors 

 were effective in limiting primary production. Differences in micronutrient 

 relationships between the cold surface waters «-l°C) which contain 

 large portions of Polar Water and the warmer surface waters which 

 contain large amounts of Atlantic Water are evident. Reactive phosphorus 

 and reactive silicate values were often high in the colder surface 

 waters, and nitrate concentrations were often quite low. The discussion 

 of the high reactive phosphorus/nitrate ratios of the Polar Water 



39 



