68 THE OCEAN 



been briefly described in Chapter I., so we 

 may now proceed to a consideration of the 

 distribution of temperature in the great oceans. 

 Distribution of Temperature, — Broadly speak- 

 ing, the distribution of temperature at the 

 surface is dependent on geographical position, 

 the water being ice-cold at the poles and hav- 

 ing a temperature of over 80° F. at the equator, 

 but the position of the isothermal lines is 

 much modified by prevailing winds, by the 

 situation of land-masses, and by the position 

 of the areas of barometric maxima and minima. 

 There is a nearly continuous broad band 

 around the equatorial regions of the globe 

 in which the mean annual surface temperature 

 exceeds 80° F. To the north and south of 

 this band the temperature decreases gradually 

 towards the polar regions. A mean tempera- 

 ture exceeding 60° F. is found within the 

 latitudes of 40° north and 40° south, except 

 in the North Atlantic, where it extends beyond 

 the parallel of 40° N. A mean temperature 

 of 40° F. corresponds in the southern hemi- 

 sphere with a latitude of about 55° S., while 

 in the North Atlantic it extends to the north 

 of lat. 70° N., beyond the North Cape. About 

 16 per cent, of the entire ocean surface has 

 a mean temperature below 40° F. 



In the Atlantic and eastern portion of the 

 Pacific, areas of high surface temperature 



