26 



Large-Scale Features 



Water on the offshore side of the Stream. Fig. 5, b, shows the corresponding 

 values of salinity. One sees that there are three clearly defined thermal 

 regions in the ocean : (i) a surface layer several hundred meters in depth 

 which is subject to seasonal thermal variations; (ii) a zone of marked verti- 



TEMPERATURE , 'C 

 0' 5* 10* 15' 20* 25' 



I .... I . I '■ I ■'■■■'''■■ I 



Fig. 5. Temperature and salinity soundings, a, temperature soundings at 

 two different seasons of the year in slope and central water. The depth scale is 

 in kilometers. The temperature is in degrees Centigrade. 6, salinity soundings 

 at two different seasons of the year in slope and central water. The depth scale 

 is in kilometers. The salinity unit %o means parts per thousand. 



cal temperature gradient, called the main thermocline ; and (iii) a very large 

 mass of cold deep water below 1500 m. 



Fig. 6 shows the average volume transports of the various surface cur- 

 rents in the North Atlantic Ocean in millions of cubic meters per second 

 according to Iselin (1936). Fig. 7 is a block diagram of the gross features of 



