1 42 The Three-dimensional Temperature Distribution and its Variation in Time 



thermal equator is displaced towards the north so that the temperature maximum 

 lies in annual average at 7° N. The large contrast between the Northern and the 

 Southern Hemisphere in sea surface temperature is particularly noticeable; in the 

 Northern Hemisphere this temperature is on the average about 2°C warmer in all 

 latitudes. It is especially pronounced in the Atlantic where between 50° and 60° N. 

 the difference is almost 7°C. This is due to the system of currents in the North Atlantic 

 Ocean and especially due to the general coastal configuration of the North Atlantic 

 which separates the water masses of the North Polar Basin, so that its cooling effect 

 only shows to a small extent in the North Atlantic. Analogous separation occurs in 

 the North Pacific. In the Southern Hemisphere, on the other hand, the three oceans 

 are fully exposed to the influence of the Antarctic. A further factor intensifying the 

 temperature differences in the Atlantic is the projection of the South American con- 

 tinent out to Cape San Roque in a latitude of 7° S. which deflects a considerable part 

 of the Southern Hemisphere tropical water across the equator into the Northern 

 Hemisphere. 



The warmest part of the tropical ocean is a long belt with a temperature between 

 28 °C and 29 °C extending from the central Indian Ocean at about 60° E. through 

 Australian Asiatic waters to about 1 75 ° E, in the western Pacific. The western half 

 in the tropics is warmer than the eastern half and this circumstance is one of the most 

 important features of the temperature distribution in the Pacific. All the other oceano- 

 graphic factors are influenced in that way. In addition to this large area at a tempera- 

 ture above 28 °C there is also a part of the Red Sea and a small isolated area off the 

 south-west coast of Central America where the temperature rises above 28 °C. The 

 total oceanic area with a temperature higher than 28 °C amounts to 21-6 million km^ 

 of 6% of the total ocean surface. In the Atlantic, areas with the mean annual tem- 

 perature above 28 °C are entirely missing. 



Table 66. Area {in million square kilometres) with mean annual 

 temperature above 25 and above 20 "^C 



Table 66 shows total areas with mean annual surface temperatures above 25 and 

 20°C; the warm parts of the oceans aie really of enormous horizontal extent. More 

 than half of the entire ocean surface is warmer than 20 °C and of this 50% more 

 than two-thirds has a mean annual temperature above 25 °C. The oceans over much 

 of their surface are decidedly warm. The coldest parts of the ocean are at — 1-7°C 

 (close to freezing point of salt water) in the North Polar Basin and in the circum- 

 polar Antarctic waters. 



Referring to the general distribution of the isotherms at the sea surface the following 

 points may be mentioned: 



