Paper 6 



COASTAL UPWELLING OFF WESTERN NORTH AMERICA/. 1976 



Craig s. Nelson 



INTRODUCTION 



The nearshore marine environment off western North America is 

 markedly influenced by processes of coastal upwelling and 

 downwelling. Upwelling is widely recognized as a fundamental 

 factor in the formation of nutrient rich surface water favorable 

 to primary production. Wind induced surface layer divergence may 

 also dramatically modify nearshore marine climate* and may act as 

 an important driving mechanism for continental shelf/slope 

 ci rculation.^ 



Variations in biological communities often occur nearly in phase 

 with the predominant seasonal cycle of coastal upwelling. Major 

 fluctuations in the intensity of coastal upwelling also occur at 

 frequencies corresponding to the diurnal sea breeze* to synoptic 

 "events"* and to interyear variations in the location and 

 intensity of the Large scale atmospheric circulation system over 

 the northeastern Pacific. Anomalously strong or weak upwelling 

 may be related to major fluctuations in stock recruitment 

 (Parrish 1976) which are likely to have subsequent effects higher 

 in the food chain. 



Bakun (1973) computed an index of coastal upwelling based on 

 calculations of surface wind stress derived from analyzed fields 

 of surface atmospheric pressure. These fields are routinely 

 oroduced by the U.S. Navy Fleet Numerical Weather Central. The 

 "upwelling index" is defined as the offshore directed component 

 of Ekman transport* and is considered to be a gross measure of 

 the amount of upwelling required to replace water transported 

 offshore in the surface layer. Negative values of this index 



'Pacific Environmental Group* National Marine Fisheries Service* 

 NOAA* Monterey* Cm 95940. 



'Niiler* P. P.* and C. N. K. Mooers. 1977. A model shelf 

 dynamics program. A report to the National Science Foundation* 

 Office of the International Decade of Ocean Exploration* January 

 1977. 



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