Dissolved Nutrients 



271 



Basin, whereas in the anaerobic zone be- 

 neath it is similar to that in Santa Barbara 

 Basin. Thus the concentrations of dissolved 

 phosphate in the sediments of the three 

 basins closely parallel the Eh'^. The nature 

 of the chemical control is not known, but 

 the parallelism of phosphate and Eh has 

 been noted in other kinds of sediments (Rit- 

 tenberg, Emery, and Orr, 1955). Probably 

 pYi also plays a role through its control of 

 the solubility of calcium phosphate. Com- 

 parison with immediately overlying water 

 shows some enrichment at the bottoms of 

 all three basins, as though regenerated 

 phosphate is diffusing or otherwise moving 

 upward out of the sediment into the over- 

 lying waters. Precipitation must, however, 

 be occurring at certain depths in Santa 

 Monica Basin sediments because the con- 

 centration of phosphate at those depths is 

 less than that of the sea water which origi- 

 nally occupied the interstices between the 

 sediment grains. Variations of total phos- 

 phorus at depth are probably more related 

 to grain size (and thus to composition of 

 the sediment) than to solution or deposition 

 of phosphate, because the content of phos- 

 phorus in detrital sediments far exceeds the 

 amount present in organic matter deposited 

 in the sediments. Unlike that for the nitro- 

 gen components, the concentration of dis- 

 solved phosphate is controlled by solubility 

 equihbria rather than by bacterial oxidation 

 of organic matter. Nevertheless, the uni- 



formity with depth of the ratio of dissolved 

 nitrogen (mostly ammonia) to dissolved 

 phosphate (Fig. 219) shows that the rates of 

 regeneration of phosphate and ammonia at 

 all depths are similar. 



Silica, the third nutrient, is even more 

 concentrated in detrital sediments than in 

 the organic matter that is deposited with 

 the sediments. Its release, even more than 

 that of phosphate, is a pure solubility prob- 

 lem. In the sediments of each basin the 

 dissolved siUca increases with depth to max- 

 imum values of 2300, 2030, and 1400 /xg- 

 atoms/liter in Santa Barbara, Santa Cata- 

 lina, and Santa Monica Basins, respectively. 

 These concentrations bear a direct relation- 

 ship to/'H: 8.20, 8.05, and 7.64, respectively; 

 evidently the amount of dissolved silica is 

 closely controlled by /?H, as might be ex- 

 pected. Even at the tops of the cores dis- 

 solved silica is several times more concen- 

 trated in interstitial than in basin waters, 

 which reach about 160 jug-atoms/liter. 

 Somewhat greater values occur in the water 

 immediately overlying the bottom (Fig. 218). 

 A comparison with the concentration of sil- 

 ica in other kinds of waters (Fig. 220) shows 

 that dissolved silica in interstitial waters of 

 basin sediments is far more concentrated 

 than in waters of the ocean or of fresh- water 

 lakes. Only in some ground water, streams, 

 and alkaline lakes does silica become so 

 concentrated. This relationship is such as 

 to suggest that dissolved silica can become 



Figure 219. Depth distribution 

 of dissolved phosphate and of 

 nitrogen-phosphate ratio in 

 sediments and overlying water 

 of three basins. From Ritten- 

 berg, Emery, and Orr (1955, 

 Fig. 5). 



DISSOLVED N - DISSOLVED P 

 2 5 10 20 50 100 200 50 



J I L 



100 200 



PO4 -P JJl A/L 



SANTA CATALINA BASIN 

 SANTA MONICA BASIN 

 SANTA BARBARA BASIN 



