574 EIGHTH PACIFIC SCIENCE CONGRESS 



1952), attaining four miles a day (8 to 10 cm./sec). This flow was 

 accelerated by southeast winds, which are dominant in winter. 



In the study of the data it was found that the currents decreased 

 with depth to about half the surface value at 300 metres. Below this 

 depth there was little or no intrusion of water from the west, so that 

 there was only a slow northward movement. 



It was considered instructive to examine the data by the method 

 of isentropic analysis (Rossby, 1936; Montgomery, 1938), which does 

 not assume gradient flow. However, it was kept in mind that the pro- 

 cess of vertical mixing, which would limit the validity of this ap- 

 proach, is likely to be strongest near the coast. The principal patterns 

 of flow suggested by the isentropic charts was similar to those shown by 

 the calculated dynamic topography, although considerable differences 

 in detail were overlooked. However, there was no more definition of 

 flow in these isentropic analyses than in the gradient studies. It was 

 evident that in the summer the area was dominated by eddies or very 

 slow indeterminate movements, with no more than a general tendency 

 northward. 



Wlien surface waters are carried seaward by winds from the north- 

 west they are replaced in part by the upwelling of deep waters along 

 the coast. This upwelling has been advanced by a number of authors 

 as an explanation of the cold saline waters found along this coast in 

 the upper zone, during the summer (Igelsrud et ah, 1936; TuUy, 1938: 

 Pickard and McLeod, 1953) and by Sverdrup (1941), who observed simi- 

 lar phenomena along the California coast. 



Figure 6 shows the disposition of isotherms and isosalines along 

 a line normal to the coast of Vancouver Island, during each of the sur- 

 veys. The March 1952 cruise followed a period of fairly strong varia- 

 ble winds which were predominantly southeast. There is no indication 

 of upwelling associated with these data. The other three cruises were 

 preceded by predominantly northwest winds, and show a distinct rise 

 of the isotherms and isosalines adjacent to the coast. This tendency 

 is most marked in August 1951, w-hen the northwest \vinds were most 

 prolonged and consistent. 



In the classical example of upwelling found off California, the 

 offshore movement of the waters results in the accumulation of light 

 surface water in a narrow stream parallel to the coast, and some dis 

 tance from it. Off the British Columbia coast the northwest winds 

 oppose the prevailing current and no coastal stream is developed. How- 

 ever, the offshore tendency persists and results in a degree of upwelling. 

 As the water upwells in summer it is diluted by coastal drainage, warmed 

 by insolation, and dispersed in a narrow north flowing coastwise cur- 

 rent which has been described by Tnlly (1938). This current loses 



