Large-Scale Features 



27 



the North Atlantic Ocean. The observer is standing high above the Gulf of 

 Mexico looking toward the northeast, that is, toward England. The ocean 

 is dissected to show its structure with depth as well as along the surface. 

 Block 1 represents the westernmost part of the North Atlantic, thus 

 including the Gulf Stream. Block 2 represents the Sargasso Sea. Block 3 

 represents the area of the North Atlantic Current, its eddies, and its 



Fig. 6. Iselin's sketch showing sources (broken lines) and pattern (soUd 

 lines) of the Gulf Stream System. In the western half of the ocean each trans- 

 port line represents about 12 x 10" m.*/sec. From Iselin (1936, fig. 48). 



multiple currents. The deep water of the ocean, which is indicated by the 

 darkest shading, apparently does not circulate as rapidly as the surface 

 waters. With an average age of some several centuries, it is only slowly 

 renewed by sinking, in very limited areas such as that indicated by the 

 crooked arrow in Block 4. Water between 5 and 16° C. lies mostly in the 

 region of the main thermocUne and is shown by intermediate shading in 

 all the blocks. We have no direct information about its sinking rate, but 

 there are some indications that this intermediate water is formed in the 



