TEMPERATURES AT THE SEA SURFACE 53 



estimâtes thus arrived at an average température for the whole 

 mass of the oceanic water of the three great océans. The 

 averages given by Krùmmel are — 



Atlantic. Indian. Pacific. Whole Océans. 



4-02° C. 382° C. 373° C. 3-83° C. 



The température of the great mass of oceanic water, 

 approximately 38-8° F., is thus low, and shows that the océans 

 are in the main extremely cold. The main source of organic 

 material in the sea is fortunately met with in cold-water areas. 

 At the same time it must not be forgotten that the upper layers 

 in which the plankton is produced are by far the warmest, and 

 ihere is a gênerai tendency for warm surface currents to flow 

 from the Equator to the Pôles. Of thèse currents the " Gulf 

 Stream " is the leading example. 



This Gulf Stream varies in strength from year to year, and 

 according to many oceanographers, such as Pettersson, there 

 is a direct connection between the thermal conditions of the 

 Gulf Stream in North European waters and the climate of 

 the adjacent countries, and possibly also in the migration of 

 certain fish of économie importance, such as herring (p. 60). 



A detailed considération of the distribution of température, 

 both horizontal and vertical, in the varions océans and seas of 

 the globe is beyond the scope of this work. 



That, however, it is not a question of purely theoretical 

 interest a few instances will prove. 



Most fîsh of économie importance are found in waters with 

 a certain range of température, and in waters above or below 

 certain ranges no fish of commercial value are met with (see 



P- 35)- 



In depths of 100 mètres (54-6 fathoms) the températures 



correspond to and change with the surface températures as a 



gênerai rule. At 200 mètres (109 fathoms) there is a perceptible 



gênerai lowering of the température. At 400 mètres (218 



fathoms) there are still wide areas in the tropics where the 



température is 10° C. (50° F.) or over, and the influence of 



