2()2 ['iuv( rsitji of Califoniia I'liblicafioiis in Zoology [Vol. 15 



perature above that of the surrounding water. Furthermore, the high 

 temperatures of the same region, shown especially well by plate 7, 

 confirm this hypothesis. A similar phenomenon is also indicated in 

 Santa Monica Bay by plates 6 and 10, and the southwesterly flow 

 revealed by the isotherms (pi. 6) would tend to produce a counter- 

 clockwise \vhirl. The distribution of gas content would evidently be 

 especially valuable in determining tlie details of such a complex 

 circulation. 



Several circumscribed areas of low salinity off the mainland arc 

 shown in plate 10; on comparing this with plate 6 the location of these 

 areas of low salinity will be found to correspond with those areas of 

 cold water heretofore discussed (see p. 260). Again, the low salinities 

 off the Cortes Bank correspond to the low temperatures (pis. 5 and 

 13). These low surface salinities may seem at first to contradict the 

 hypothesis of upwelling, since it is generally believed, as stated by 

 Sumner (1914, p. 82), that "according to the theory of upwelling, 

 we should expect to find water of a higher salinity, derived from the 

 deeper parts of the ocean, in the immediate neighborhood of tlie west- 

 ern coast" [italics mine]. However, the effect of upwelling on the 

 distribution of salinity is not as simple as it would on first thought 

 appear. It depends mainly upon the vertical distribution of salinity 

 and on the velocity of upwelling. As demonstrated on page 277, in 

 any region characterized as this one is by a minimum salinity at some 

 intermediate depth (see p. 272) and a very low velocity of upwelling 

 (see p. 278), lower salinities would be expected in the upper levels. 

 Hence the hypothesis of upwelling proposed to account for the low 

 temperatures is well supported by the distribution of salinities. 



However, as shown by plates 13 and 14, figure 19, high salinities 

 sometimes occur inshore. The interaction of a number of local con- 

 ditions which influence salinity, such as humidity and velocity of the 

 air, temperature of the water, solar radiation, etc., may at times over- 

 come the effects of upwelling, which depends largely upon the wind 

 (see p. 277) and is therefore .subject to wide variations. Water of low 

 temperature and salinity may have its temperature increased by solar 

 radiation, but the humidity of the air may be so high and its circulation 

 so feeble that evaporation would be very slow and little if any increase 

 in salinity could result. On the other hand, conditions favoring rapid 

 evaporation and therefore high salinities may be associated with influ- 

 ences having little tendency to raise the temperature. In fact, an 

 actual decrease in temperature might result from the tendency of 



