106 



Water 



'oxygen- ml/l 



Figure 93. Relationship between dis- 

 solved oxygen and water temperature for 

 Marine Life Research cruises of February 

 and July 1950. Data for other cruises are 

 similar. The plot includes only depths 

 between 100 and 500 meters. Contours 

 show percentage of Southern Water with 

 only 10 per cent of points differing by 

 more than one contour interval. 



oxygen contents inshore of the continental 

 slope were found by Sverdrup and Fleming 

 (1941) to be less than the computed ones. 

 They interpreted the deficiency as caused by 

 oxidation of organic matter settling through 

 the water from the area of high production 

 near the surface. The greatest deficiency in 

 oxygen content occurs in the area of Santa 

 Barbara Basin. For the whole region the 

 deficiency in 1938 was 40 to 80 ml in a 1 sq 

 cm column of water between 50 and 700 

 meters. This corresponds to an annual pro- 

 duction of 500 to 1000 grams of dry plank- 

 ton per square meter, with the higher figure 

 being more nearly correct, because the data 

 omits oxygen consumption in the 0- to 50- 

 meter depth zone and because some of the 

 organic matter falls entirely through the top 

 700 meters of water without becoming com- 

 pletely oxidized. For comparison. Holmes 

 (1957), using a radiocarbon method, ob- 

 tained a daily production of about 0.5 

 grams of carbon per square meter per day; 

 this corresponds to about 420 grams of dry 

 plankton per square meter per year. 



One result of the oxidation of organic 



matter falling through the water column is 

 the regeneration of nutrients; accordingly, 

 the nutrient content of the water must be in 

 approximate inverse proportion to the oxy- 

 gen content. Such is true for phosphate- 

 phosphorus, the only nutrient that has been 

 determined routinely off southern Cali- 

 fornia (Fig. 94). In addition to bearing an 

 inverse ratio to oxygen, the phosphorus 

 concentration appears to show a seasonal 

 variation, being somewhat more abundant 

 in water of a given temperature during July 

 than February (Fig. 95). This may be a re- 

 flection of greater regeneration after the 

 spring season of plankton blooming than 

 occurs during the winter, but it is curious 

 that the oxygen content is not markedly 

 lower during July than February. This 

 problem of regeneration of nutrients deserves 

 more attention than has been given it in the 

 region off southern California. 



Basins 



About 5 per cent of all the water atop the 

 continental borderland in the area of Chart 



