276 



WOOSTER AND REID 



[CHAP. 11 



(a) (b 



1000 

 



1000 



1000 



DISTANCE OFFSHORE (km) 



Fig. 17. Profiles across North Atlantic Current at 51.5°N, August, 1958. (a)-(d) as in 

 Fig. 6. (After Fuglister, 1960.) 



5. Biological Implications 



Production of organic matter in the sea is limited to the surface layers where 

 the supply of radiant energy is sufficient to permit photosynthesis. Since the 

 vertical distribution of the nutrient elements on which the process also depends 

 usually shows marked depletion in the surface layers and much higher con- 

 centrations in and below the pycnocline, regions of high productivity are found 

 where the upward vertical transfer from this reservoir of nutrients is most 

 effective. The exchange between near-surface and deeper waters takes place 

 most commonly (1) in high latitudes, (2) along the equator, and (3) in coastal 

 regions, particularly on the eastern sides of oceans (Wooster and Ketchum, 

 1957). Such exchange along the eastern boundary coasts is attributed to the 

 coastal up welling process discussed above. High productivity is also favored by 

 the shallow thermocline along such coasts, since the mixed layer is usually 

 shallower than the "critical depth" (which depends on the amount of incoming 

 radiation, transparency of the water and the energy level at the compensation 



