260 Ihrivcrsiii) of ('alifoniia Publications in- Zoology [Vol. 15 



observations made by officers cruising in the Pacific and represented 

 on the U. S. Meteorological Charts of the North Pacific Ocean. 



While this is the characteristic direction of surface drift, a local 

 and more restricted northward drift of warm water is also shown near 

 the mainland off Point Loma by plates 7 and 8. 



The temperatures near the east coasts of the islands are higher than 

 those farther from their shores, as shown off Catalina by plates 5 and 

 6 and off Guadalupe and Cerros islands by plate 9. This diffei'ence 

 in temperatiires would be expected because in a deep region, say ex- 

 ceeding two hundred meters, the heat received by any given layer of 

 water is largely derived from the fraction of the solar radiation 

 directly absorbed by that layer. In a shallow region, however, addi- 

 tional heat is communicated by convection and conduction from the 

 bottom. Thus the heat is concentrated in a smaller volume in shallow 

 than in deep water. Also the convection currents due to these high 

 temperatures tend to produce high temperatures for some distance 

 in all directions from the shallow region. 



In contrast to the above results, numerous regions of .shallow water 

 off the mainland have lower temperatures than the water in their 

 immediate vicinity. For example, in plate 9 two such regions are 

 shown just south of Cape San Quentin, in one of which values as low 

 as 13° C are found with a progressive increase in all directions, and in 

 the other an area having the low temperature of 15° C is circum- 

 scribed by warmer water and the coast. Three other cold areas shown 

 by the same plate are also surrounded by the coast and by warmer 

 water. Plate 6 reveals the same phenomenon near Point Fermin and 

 also north of Point Dume ; while in Santa Monica Bay much higher 

 temperatures jjrevail. Since, as was pointed out above, solar radiation 

 would be expected to produce higher temperatures in areas of shallow 

 water, there must be a flow of water from some colder region wher- 

 ever the surface temperatures are so low. Evidently a surface flow 

 will not account for these low temperatures, because several of these 

 areas are completely circumscribed by the coast and water of a higher 

 temperature. Upwelling of cold bottom water appears to be the 

 only type of circulation that could produce such a distribution of 

 temperatures. 



Furthermore, the contour maps (pis. 1-3) reveal a striking cor- 

 relation between the location of these areas of cold water and the 

 submerged valleys or other regions in which the depth increases 

 rapidly witli increasing distance from the coast. For example, the 



