1916] McEwni: IlfidnKjraphiv Ohscrvntions of Scripps Iiisfil titioit 277 



heating, evaponitioii, etc., to take i>lace duriug brief intervals of time 

 alternating with intervals during which the column is elevated. Dur- 

 ing the intervals of elevation the salinity will be reduced at all depths 

 above that of its minimum value, and raised at all greater depths, but 

 during the other intervals it will be raised at all depths above that 

 of its minimum value and lowered at all greater depths. Hence, as 

 was shown to be true of temperatures, a steady state must ultimately 

 arise in wliieh the salinity is lower above the depth of its minimum 

 value but is higher below that depth. If, as is the case in nature, the 

 alternating time-intervals be indefinitely reduced until all processes 

 occur simultaneously, tlie final temjierature and salinity distribution 

 will be unaltered. 



The conclusion just reached regarding the etfeet of upwelling on 

 the salinity holds only when other local conditions tend to produce a 

 minimum value at some intermediate depth, and when the vertical 

 velocities are not too great. In the absence of such a minimum value 

 of the salinity or in case the upwelling is sufficiently active, high 

 salinities would be expected at all depths of inshoi-e regions. 



By applying Ekman's hydrodynamical theory of oceanic circu- 

 lation to observations other than of temperature and salinity made off 

 the west coast of North America, the conclusion (McBwen, 1912) was 

 reached that there must be an upwelling of deep water along the coast 

 from 40° N to about 25° N. An important principle deduced by 

 Ekman is that a wind blowing parallel to a coast will not only move 

 the water in its own direction but will deflect a surface layer of less 

 than one hundred meters in thickness to the right of its own direction. 

 Hence a wind blowing in the proper direction with respect to a coast 

 will remove the surface water and thus reduce the water pressure at 

 all distances from the bottom. This reduction of pressure will then 

 give rise to a flow of bottom water toward the coast, and consequently 

 to the surface near the coast. By considering quantitatively the re- 

 lation between wind velocities and the mean monthly surface temper- 

 atures between the west coast of North America and 140" W^ the wind 

 velocity was demonstrated to be an important if not the main cause 

 of upwelling (]\IcEwen, 1912). It also follows from Ekman's theory 

 that the greater the inclination of the bottom, in the neighborhood of 

 a coast, the narrower will be the belt near the coast into which a given 

 volume of bottom water intrudes, and therefore the greater will be the 



3 See U. S. Meteorological Charts of the North Pacific (1908-1911) for data 

 on the winds, and Thorade (1909) for the temperature distribution. 



