80 



flow occurs. Whatever the action, the mechanism is unimpor- 

 tant to this discussion. 



The cold water unit in the southern part of the bay is 

 usually most intense along the western shore of the Palos 

 Verdes Hills. Frequently its extent is minor and the tempera- 

 ture differential between it and adjacent water units is great. 

 At such times it is close to shore with a steep thermal gradient 

 separating it from the offshore water. At other times, the 

 unit spreads into the bay and along the coast as far north as 

 Redondo. Both temperature differentials and gradients are 

 small during such an expansion. 



The existence of these cold water units almost contin- 

 uously throughout the year establishes thermal conditions which 

 do not occur in any other parts of the bay. The occurrence 

 along the Malibu coast is easily explained by the dominant 

 westerly winds with resultant upwelling action. That along 

 the Palos Verdes shore is not likely due to wind action because 

 the orientation of the coast to the winds is such that surface 

 water should be directed toward the shore rather than away. 



There appear to be two possible explanations for this 

 cooler water. It is known that unusually rugged topography 

 on the sea floor in shallow water areas can result in the 

 projection of subsurface water to the surface (Stevenson and 

 Gorsline, in press). The region of cold water in this part 

 of the bay fluctuates across Redondo Canyon, the shelf pro- 

 jection south of the canyon, and the narrow shelf adjacent to 

 the Palos Verdes Hills. It is not unreasonable to assume, 

 therefore, that tidal currents and internal waves flowing over 



