with a high rate of primary production in the Labrador Sea occur where 

 fronts between two water systems are found — specifically at the 

 fronts on both sides of the irminger Current off east and south Green- 

 land and "the front between the Labrador Polar Current and the 

 subarctic water in the western part of the Labrador Sea" (Hansen, 

 1959, p. 309). The surface productivity is indirectly indicated by the 

 nitrite distribution previously mentioned. Gillbricht (1959) has 

 estimated from turbidity measurements in the Irminger Sea that 

 40 percent of the turbidity in surface waters is due to living plankton 

 and 60 percent to detritus. Regeneration of the detrital material 

 would lead to the high subsurface nutrient concentrations seen in 

 figures 32 through 36. The exchange is a dynamic one, since Steeman- 

 Nielsen (1958) considers that the surface production, in turn, is 

 stimulated by the formation of eddies bringing nutrient-rich water 

 to the surface. It is noteworthy that the coastal currents show 

 reduced nitrite concentrations and that the available productivity 

 measurements indicate lower levels on the coast and in the center 

 of the basin than near the fronts (Hansen, 1959). The pattern of 

 the high near-surface nutrient concentrations can therefore be used 

 as a general indicator of the boundaries of surface water masses 

 across the section. 



High nutrient concentrations in deep water represent a different 

 water-mass source. Smith, Soule, and Mosby (1937, p. 192) have 

 presented the hypothesis that the bottom water of the North Atlantic 

 Ocean is formed in winter by the chilling and sinking of the surface 

 waters in the north-central Atlantic Ocean proper. This southward- 

 flowing deep water follows the Labrador slope. We suggest that 

 this flow is marked by the prominent nutrient concentrations occur- 

 ring as distinct high values in the deep water on the western edge of 

 the Labrador basin. An influx of Atlantic water from the Irminger 

 Sea is required to compensate for the loss of the deep water. Kalle 

 (1957) has shown high phosphorus concentrations extending to 

 depths of 1,500 D-meters near the mid-Atlantic ridge in his sections 

 to the east of Greenland. It is also possible that some of the deep 

 water nutrient concentrations represent continuing decomposition, 

 although the separation of the deep water concentrations as discrete 

 entities suggests a reasonable distinction in the sources providing 

 them. 



The formation of deep water is generally considered an annual 

 process, with some variation in magnitude from year to year. In 

 contrast to the well-defined pattern that can be constructed from 

 the nutrient distribution data for 1963, observations of the previous 

 year were much less striking. Distribution profiles for inorganic 

 phosphate, nitrate-nitrogen and silicate-silicon may be compared. 

 (See Corwin and McGill, 1963.) Much more diffuse patterns of 

 distribution will be noted for summer 1962, with the widespread 



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