OCEAN TEMPEEATUBES 



409 



Water Sc/rface 



results. In dealing with mean annual values we can assume all con- 

 ditions to be independent of the time, from which it follows that the 

 total amount of water in a given volume remains constant and the 

 total amount of salts remain constant. Therefore the rate of flow of 



water and salts into the volume must 

 equal the rate of flow out of the 

 volume. 



This principle will be applied to 

 two different volumes, thus giving two 

 estimates of the velocity of the up- 

 welling. First, consider a vertical 

 column (fig. 18) whose cross section 

 is a square of unit area and whose 

 base is at the depth y 2 where the 

 salinity has its minimum value (Mc- 

 Ewen, 1916, p. 272). 



The explanation of symbols used 

 follows : 



Coast 



Bottom 



S = the salinity at any depth y. 

 $ = the salinity at the surface. 

 S 2 = the salinity at the depth y 2 . 

 r 2 W l = the vertical velocity at the 



depth y 2 , W i is the maximum 



value, and corresponds to large 



values of y (table 13). 

 y = the horizontal velocity. 

 E = ihe rate of evaporation at the 



surface. 



Fig. 18. Eectangular volume of 

 water from the depth y 2 of mini- 

 mum salinity to the surface, used 

 in determining the velocity of up- 

 welling from salinity. 



A flow into the volume is regarded 

 as negative, and a flow out is regarded 

 as positive, the vertical distances and 

 velocities are regarded as positive 

 when directed downward from the surface, and horizontal distances 

 and velocities are positive when directed away from the coast. 

 Because of the invariability of the amount of water in the volume 



r 2 W 1 E+fvdA = 



(202) 



