188 MARION AND GENERAL GREENE EXPEDITIONS 



northward of Cape Farewell up to Davis Strait indicate that the 

 bottom water of the Labrador Sea is formed in the latter area and 

 moves southward. The low oxygen values in the upper layers at 

 the southern end of the section correspond to the northern border of 

 the Atlantic Current. The rapid downward decrease of oxygen in 

 Baffin Bay arises from the pocketing of water there by 600 to 700 

 meter thresholds. 



As has been demonstrated by consideration of the distribution of 

 oxygen the cold bottom water of the Labrador Sea is the result 

 of wintertime chilling which affects the bottom water through 

 vertical convection. The salinity of the water in the region where 

 vertical convection may take place, however, is lower than that 

 of the bottom water actually observed in the summertime. The 

 bottom water must therefore be a mixture with saltier water, which 

 water is typified by the Irminger-Atlantic Current. In figure 146, 

 page 185, the temperature-salinity relation of the Irminger-Atlantic 

 water, based on summertime observations off Cape Farewell, has 

 been drawn as a solid line. The upper part of this line grades away 

 from the core into insolated surface water and the lower part grades 

 off into the colder water below the axis of the Irminger Current. 

 The apex has been taken as most characteristic of Irminger-Atlantic 

 water. If this is one of the components of the bottom water, the 

 other component will lie along a line through the characteristics of 

 the bottom water and Irminger-Atlantic water. Such a line has 

 been drawn on figure 146, page 185. In selecting the characteristic 

 point for the bottom water the lowest bottom temperature indicated 

 by our observation (1.57° C. at General Greene station 2033) has been 

 selected as having been least modified since formation, and the 

 potential temperature has been used in order to translate the mixture 

 into terms of shallow water phenomena. The other component then 

 must lie along the broken line in the salinities lower than 34.91%o. 



If vertical convection, arising from winter chilling, accounts for 

 onej of the components of the bottom water, it must take place off- 

 shore from the more rapidly moving Labrador and West Greenland 

 Currents. Also, the density gradient prior to the beginning of winter 

 must not be so great as to require water temperatures lower than 

 about —1.8° C. to establish vertical convection. If complete hori- 

 zontal stagnation is assumed, the maximum temperature at which 

 vertical convection to bottom can occur may be found from the 

 average salinity of the water column and the density of the bottom 

 water observed in summer. Such computations of the maximum 

 temperature to which the water must be cooled in order to estab- 

 lish vertical convection from the surface down to successively deeper 

 levels have been made for a number of stations. The maximum 

 temperature values have been plotted for the GodtKcmVs section 

 from Resolution Island to Fiskernaessett and are shown in figure 149. 

 As has been mentioned above, the upper limit of salinity of the 

 bottom-water component produced through vertical convection is 

 34.91%o. The broken line shown in figure 149 connects points, the 

 average salinity of the column of the water above which is 34.91%o. 

 A similar line is shown for 34.81%o average salinity of the super- 

 posed column of water, since 34.81%o is the approximate salinity 



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