274 Univcrsily of Califoniia I'uhlkations in Zoology [Vol. 15 



served below the surface were thought to be due to erroneous deter- 

 minations. It was only after we began making observations with the 

 Ekman reversing water bottles at short intervals of five meters or less 

 between the surface and one hundred meters that we became convinced 

 of the presence of a subsurface minimum. Finally, these results 

 demonstrate the need of more intensive observations in the upper 

 hundred meters of other regions. 



F. CERTAIN THEORETICAL IMPLICATIONS OF THE 

 OBSERVATIONS 



In general, our temperature observations made at all levels off the 

 west coasts of the mainland and the islands reveal an increase in 

 temperature as the distance from the coast increases. Furthermore, 

 our observations of salinity made at all levels above the depth of its 

 minimiim value (see p. 272). which varies from sixty meters in deep 

 to less than ten in shallow water, show that on the average the water 

 adjacent to the coast has the lowest salinity. That is, in this upper 

 mass of water the salinity varies in the same general way as the 

 temperature, though not as regularly. Again, at all levels below the 

 depth of minimum salinity the highest salinities occur adjacent to 

 the coast, and there is a fairly regular decrease as the distance from 

 the coast increases. 



The presence of cold water has been repeatedly observed in various 

 coastal regions. In order to account for this phenomenon some hypoth- 

 esis involving the upwelling of deep water into these regions has been 

 proposed by several investigators ; as revealed in the preceding pages, 

 there is strong evidence in favor of such a circulation off the California 

 coast. 



An uiJwelling of deep cold water would evidently reduce the tem- 

 perature at any higher level and would also tend to maintain the 

 salinity in the upper levels at a value below the normal, if the rate 

 of upwelling is not too great. The reason for this is as follows : Since 

 sea-water is a dilute solution of various salts, its osmotic pressure 

 varies as the product of its concentration or salinity, by its absolute 

 teiu|)crature. As shown by tlic following table, this product is nearly 

 constant at all depths below that corresponding to the depth of mini- 

 mum salinity, but increases from there to the surface. Therefore the 

 osmotic pressure must be essentially constant below this depth, but 



