HYDROGRAPHY 



151 



the Faroe Channel, where the " Wyville Thomson " ridge 

 prevents the cold Arctic water from invading the warm area 

 to the south of the barrier (see Fig. 6). 



Quite apart from the effect of such barriers, there are other 

 variations in the distribution of temperatures according to 

 depth, due to the circulation of special currents of different 

 temperature which mix very slowly with the surrounding 

 water. Some temperature sections through the ocean are 

 very regular in arrangement, the isotherms being horizontal 

 and arranged in order, the temperature decreasing wdth the 

 depth — a section through the Atlantic for some distance west 



fOO 



200 



CO 

 ^300 



f^400- 



600 



600' 



N 



O^er 50"* 



Warm 

 Area 



Fia. 6. — Diagram showing Wyville Thomson Ridge. 



of the Canaries shows that normal condition ; while other 

 sections are very irregular, the isothermal lines being far 

 from horizontal and curving up and down according as masses 

 of warmer or colder water are encountered. Examples of 

 such very irregular temperature sections are seen in various 

 parts of the North Atlantic. In a section from the Sargasso 

 Sea northwards towards the banks of Newfoundland the 

 isotherms, at first quite regular, rise rapidly towards the 

 surface as colder water is reached, and then spread rapidly 

 downwards in the warm Gulf Stream, to rise once more in 

 the colder coastal waters. A little way off the Newfoundland 

 Bank the isotherms, which are practically horizontal over the 



