Long-term trends and changes in the hydrography of the Faroe-Shetland Channel region 483 



be ignored, especially as much other real and circumstantial evidence points more 

 or less strongly in the same direction. In the aggregate, this evidence which, piece- 

 meal, tends to present a somewhat irregular and confusing picture from one region 

 to another, and between one organic species and another, appears to fall more 

 rationally into focus when considered from the standpoint of the characteristically 

 different water-masses in the ocean, their fluctuations in circulation and in quantity 

 (Tait, 1952, p. 92). 



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ORKNEY 

 ISLANDS 





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THE FA 



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Fig. 1 



In the seas about west and north-west Europe, for example, there are permanently 

 present at least six different and, for the most part, converging and, to some extent, 

 intermingling water-masses. These are the oceanic, continental, Arctic, Norwegian 

 Sea, North Sea and Mediterranean water-masses, each with its characteristic tem- 

 perature, but more especially sahnity, and doubtless also other properties. A variety 

 of biological and other evidence has given rise to the conception that the most signifi- 

 cantly important of these, at least in many respects, is the oceanic water-mass. Special 

 attention has accordingly been directed to the oceanic incursion into European seas 

 in an endeavour quantitatively to assess its magnitude and variations. This has been 

 done by the normal hydrodynamic method, stemming through Helland-Hansen 



