PHYSICAL OCEANOGRAPHY 



227 



In winter, heat will be radiated from the sea-surface to the 

 colder air, and the temperature will be lowered. In Figs. 159 

 and 160 two maps of the North Atlantic, one for February and sea. 

 one for August, are reproduced from Atlantischer Ozean, ein 

 Atlas, published by the Deutsche Seewarte in Hamburg. 

 In the February map the isotherm of 25' C. runs from the 

 Antilles towards the east and a little to the south, in the 

 direction of Africa, whereas in August this line lies, in the 

 western part of the ocean, as much as twenty degrees of latitude 



Radiation of 



heat from the 



rface of the 



Fig. 159.— Surface Temperature of the North Atlantic in February. 



farther north. In the same way the other isotherms have 

 more northerly positions in summer than in winter. The 

 difference between the surface-temperature in February and in 

 August is about 5° C, in some places less, in others considerably 

 more. Near land the annual variations are much greater, as in 

 the coast- water within the Norwegian skjsergaard (" skerry- 

 guard," literally: "fence of islands"), where the surface- 

 temperature in summer is i5°-20 C, and in winter only a few 

 degrees above zero. Beneath the surface the variations 

 gradually decrease, and at a depth of a few hundred metres no 

 marked seasonal variations can be traced. 



