DISCUSSION 



The physical circulation of the Labrador Sea region has been deter- 

 mined from the observations of temperature and salinity in the area. 

 The present data agrees with the picture given from such observations: 

 strongly marked surface currents are present near both coasts while 

 the waters of the central part of the Labrador Sea show a nearly uni- 

 form character. Baffin Bay is an example of a special type of basin 

 circulation found in the high latitudes, where deep water is formed 

 locally due to cooling of high salinity water, even though precipitation 

 exceeds the evaporation (Sverdrup et al., 1942, p. 150). In this type 

 of basin, stagnant water is not found. The oxygen concentration, 

 however, is much lower than that in the deep water of the Labrador 

 Sea, which is in unrestricted contact with the Atlantic Ocean circula- 

 tion. The determination of oxygen saturation shows that 90 percent 

 saturation or more occurs throughout each section in the Labrador 

 Sea. This clearly indicates the great amount of vertical mixing which 

 takes place and which produces the homogeneous nutrient distribution 

 seen in the deep water of the Labrador Sea. 



Some outflow from Baffin Bay near the sill depths occurs, as seen in 

 the nutrient distributions. The given data suggests that the main 

 core of this outflow is directed southward along the western perimeter 

 of the basin since it appears that the longitudinal midsection taken by 

 the Evergreen in 1962 lies to the eastward of the main mass of outflow- 

 ing Baffin Bay water. Water with a concentration of nutrients 

 equivalent to that found at sill depth or above in Davis Strait forms the 

 deep water maxima in the nutrient distributions in the Labrador Sea. 



The nutrient distribution patterns also present some indications of 

 the biological characteristics, since the production of phytoplankton is 

 related to the nutrient supply. It appears that the demand for 

 nutrients can be met from the relatively high concentrations present 

 near the surface. The nitrite analyses provide the most direct 

 suggestion of the probable biological environment. It has been sug- 

 gested by Vaccaro and Ryther (1960) that an increase in nitrite in the 

 upper layers of the ocean indicates the presence of a significantly large 

 standing crop of phytoplankton and an excess of nitrate. Data -of 

 Holmes (1956) show that heterotrophic phytoplankton will be nearing 

 a maximum in July while the autotrophic fraction, though declining, is 

 still abundant. Since no direct biological measurements were ob- 

 tained, the nitrite data suggest indirectly that such conditions pre- 

 sumably were present in 1962. Digby (1953) has shown that botii 

 phyto- and zoo-plankton populations reach a maximum during the 

 summer in these latitudes. Kielhorn (1952) found the zooplankton 

 populations in the central Labrador Sea characterized by relatively 

 few species but very large numbers of individuals, with sensonal 

 increases particularly evident in the late summer. 



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