Water 



On land geological and biological proc- 

 esses are largely controlled by the nature of 

 the atmosphere, but on the sea floor these 

 processes are controlled more by the over- 

 lying water, which in turn may be influenced 

 by the atmosphere. Clearly the degree of 

 freedom of movement of the water must be 

 limited by the topography of the bottom, 

 especially in this area of basins and banks; 

 thus, bottom topography as well as surface 

 source of solar energy require subdivision of 

 the water column into depth zones for ease 

 in discussion. 



Currents 



Surface 



The classical method of determining cur- 

 rents is that of computation from dynamic 

 topography in much the same manner as 

 winds can be computed from isobaric con- 

 tours of the atmosphere. Because of some 

 uncertainties in the basic assumptions the 

 computed currents are checked wherever 

 possible by current meters, drift bottles or 

 cards, and electrical measurements. Never- 

 theless, the geographical variation of water 

 characteristics remains the main indication 

 of the existence and nature of the currents. 

 Chief among these water characteristics are 

 temperature, salinity, oxygen content, and 

 nutrient concentration (usually phosphate- 



phosphorus). Nearly all the available data 

 for waters at the surface and intermediate 

 depths in the region were obtained by ships 

 of Scripps Institution of Oceanography dur- 

 ing cruises in 1937 (Sverdrup and Fleming, 

 1941) and 1938, 1939, 1940, and 1941 

 (Sverdrup and Staff", 1942, 1943, 1944, and 

 1947), and ships of Scripps, the U. S. Fish 

 and Wildlife Service, and the Cahfornia Di- 

 vision of Fish and Game (the cooperative 

 Marine Life Research Program) during 

 cruises in 1949, 1950, 1951, and 1952 

 (Scripps Institution of Oceanography, 1949- 

 1952). Two of these cruises (February and 

 July, 1950) were selected as illustrative of 

 general water conditions on the basis of their 

 relatively dense pattern of stations and their 

 completeness of data and computations, al- 

 though this year was one of somewhat colder 

 water than usual. Many of the other cruises 

 provide relatively incomplete information 

 about the region off" southern California be- 

 cause their stations were set in widely spaced 

 grids in order to provide a picture of condi- 

 tions along much of the coast between Wash- 

 ington and the tip of Baja California. 



Nearly aU cruises having adequate data 

 show the coldest water confined to an area 

 extending roughly from Point Conception 

 and Santa Cruz Island to San Nicolas Island 

 (Fig. 83). Average temperatures here be- 

 tween 1937 and 1952 range from 12.5 °C in 

 the spring to 17.0° in the fall. In contrast, 



97 



