11. EASTERN BOUNDARY CURRENTS 1 



W. S. Wooster and J. L. Reid, Jr. 2 



1. Introduction 



The general scheme of circulation of surface waters of the world ocean has 

 been gradually revealed since the first compilation of sailing-vessel drift 

 observations early in the 19th century. An important part of this circulation is 

 found in subtropical gyres, which extend from the doldrums to the mid-latitude 

 belts of prevailing westerly winds. Within these gyres, surface flow is pre- 

 dominantly anticy clonic, with zonal currents at the north and south, strong 

 persistent poleward currents on the western side, and compensating equator- 

 ward drifts in the central and eastern portions. Along the eastern boundary 

 there occur variable equatorward currents. At higher latitudes, especially in 

 the Pacific, cyclonic subpolar gyres are observed with eastern currents, which 

 in this case are directed polewards. It is the eastern boundary currents of the 

 subtropical gyres with which this chapter is primarily concerned, although 

 mention will also be made of the poleward eastern currents. 



The scientific investigation of the eastern boundary currents did not take 

 place until well into the 20th century. By the time of World War II (and the 

 completion of The Oceans) two of these features, the California and Peru 

 Currents, had been studied in a descriptive way in some detail, the former by 

 cruises of Bluefin and E. W. Scripps (Sverdrup and Fleming, 1941 ; Tibby, 

 1941), the latter by an extensive cruise of William Scoresby (Gunther, 1936) 

 and by the Carnegie P^xpedition (Sverdrup, 1930). Several crossings of the 

 Canary and Benguela Currents were made by the Meteor Expedition, and the 

 general features of the latter current were discussed by Defant (1936). Condi- 

 tions off the west coast of Australia were not studied and remain little known 

 to this day. 3 



Since the end of the war, studies of the ocean have been greatly intensified. 

 A general theory of the wind-driven circulation has been presented (Munk, 

 1950) in which some of the important features of the eastern boundary currents 

 are included. Major theoretical investigations have concentrated on the western 

 boundary currents, but some work has been done on the process of coastal up- 

 welling, a basic feature of the eastern currents, by Defant (1952), Hidaka (1954), 



1 Contribution from the Scripps Institution of Oceanography, University of California. 

 The work was supported in part by the Office of Naval Research and the Bureau of 

 Commercial Fisheries through contracts with the University of California, and in part by 

 the Marine Life Research Program, the Scripps Institution's part of the California Co- 

 operative Oceanic Fisheries Investigations. 



2 This paper was prepared jointly, the contributions of the two authors being equiva- 

 lent. In general the work was divided by hemisphere, with Reid assembling material for 

 the North Pacific and Atlantic, Wooster for the South Pacific and Atlantic, and the 

 Indian Ocean. We are greatly indebted to Dr. Ronald I. Currie who furnished us with 

 proofs prior to publication of his paper with Dr. T. John Hart on the Benguela Current, 

 and to our colleagues who read the manuscript in draft form. 



3 Since the submission of this chapter we have seen a manuscript dealing with part of 

 this area (Wyrtki, in press). 



[MS received July, 1960] 253 



