370 



[chap. 17 



oceanic areas, as illustrated by the distribution of total phosphorus in the North 

 Atlantic trade wind belt (Fig. 11, unpublished data of B. H. Ketchum, Woods 

 Hole Oceanographic Institution). High concentrations of this element obviously 

 associated with upwelling off the northwest coast of Africa spread well into the 

 mid-Atlantic. Note also indications of an upwelling of lesser magnitude of 

 unknown origin off the South American coast. 



Upwelling may also be discontinuous with time if the driving wind forces are 

 intermittent. A weakening or migration of the trade-wind belt may have 

 pronounced effects upon the hydrography of West African and South American 

 coastal waters. The resulting cessation of upwelling and warming of the surface 

 waters, in situ or through incursions of warm coastal currents, causes notorious 

 mass mortalities of fishes and other sea life which are discussed elsewhere. 



Fig. 11. Mean concentration of total phosphorus ([xg atoms/1.) in the upper 50 m of the 

 equatorial Atlantic. (Unpublished data of B. H. Ketchum.) 



Upwelling has also been reported for much of the Indian coastal waters (e.g. 

 LaFond, 1954 and 1958; George, 1953; Jayaraman and Gogate, 1957; Banse, 

 1959) as well as off the East African coast of Somali (Sverdrup et al., 1946). In 

 these cases, it is the offshore monsoon winds which produce the divergences 

 and upwelling. The seasonal periodicity of the southwest and northeast mon- 

 soons cause alternating periods of high and low fertility at different places 

 along the coast depending upon their geographical orientation. 



Indications of high productivity, in terms of the abundance of marine life, 

 in regions of upwelling are too numerous to review here. Relatively few pro- 

 ductivity measurements have been made, but the existing data (Steemann 

 Nielsen and Jensen, 1957 ; Currie, 1958 ; Holmes et al., 1957) consistently reveal 

 high rates (ca. 0.50-1.00 g carbon/m 2 /day). Measurements in the vicinity of the 

 Benguela Current included the highest values observed during the Galathea 



