TEMPERATURES AT THE SEA SURFACE 51 



two différent assemblies of organisms — e.g., fish of a given 

 species are known to fréquent exclusively water of a given 

 température, or, more accurately, water with a given range of 

 température. 



Températures at the Sea Surface. 



Lines joining places in the océan with identical température 

 are called isotherms. The first chart showing isotherms was 

 published by Maury in 1852. The surface température varies 

 from an annual average of 27-4° C. to - 17° C, the warmest 

 water being in 5° N. Lat,, the coldest from 80° N. to the Pôle 

 and 75° to 80° S. Lat. Generally speaking, the température is 

 influenced mainly by the océan currents, and this is especially 

 noticeable in the tropics. 



In high southerly latitudes there is a parallelism between 

 the isothermal lines and the degrees of latitude. 



More than half the surface of the sea has an annual average 

 température exceeding 20° C. (68° P.). The percentages of 

 the great océans which hâve this or higher température are — 

 Atlantic 501, Indian 5r7, and Pacific 584. 



Kriimmel estimâtes the average surface température in the 

 Northern Hémisphère to be 1920, in the Southern i5"97; the 

 air température averages for the Northern Hémisphère 15" 1°, 

 for the Southern i3"6° C. 



Of the three great océans, the Pacific has the warmest 

 surface water, with an average of 19-10° C, the Indian being 

 17-03, and the Atlantic, the coldest, 16-91° C. 



Practically three-fifths of the Pacific Océan lies between 

 30° N. and 30° S. Lat., whereas less than half of the Atlantic 

 is so situated. 



The coldest surface température hitherto recorded is 

 -3-3° C. off New Scotland, the highest, in the open océan in 

 the West Pacific, 322° C. The highest marine température is 

 not, as is usually given, the Red Sea (34-4° C), but the north 

 end of the Persian Gulf, with 356° C. (96° P.). The annual 

 variation of température in British waters varies from 10° to 



