The Three-dimensional Temperature Distribution and its Variation in Time 119 



2 



2 4 6 8 10 12 14 16 18 20 22 



2 4 6 8 10 12 14 16 18 20 22 

 Fig. 53. Mean vertical temperature distribution in the three oceans. 



The temperature distribution of the ocean must be regarded as quasi-stationary and 

 this leads to the deduction that the vertical temperature distribution is a phenomenon 

 closely connected with the oceanic circulation. Assuming that there was no motion in 

 the very deep ocean this vertical temperature distribution could not be understood. 

 Humboldt (1816) emphasized at an early date that the low temperature at great 

 depths in the tropical ocean can only be explained by assuming an equatorward flux 

 of cold-water masses originating in high latitudes. 



{a) The Oceanic Troposphere 



In general, the troposphere shows a well-developed subdivision into three parts. 

 In the top layer the vertical differences in temperature and salinity are very small — 

 so frequently that this top layer can be regarded as homogeneous. Its thickness is 

 seldom greater than 100 m. In the Atlantic an isothermal surface layer (tempera- 

 ture gradient <0-015°/m) is present only in the region between about 35° S. and 25° N. 

 polewards from these limits the isothermal stratification is slowly destroyed and the 

 effect of the seasons begins to predominate (disturbance zone). Table 48 presents mean 



Table 48. The quasi-isothermal top layer in the Atlantic Ocean 



