358 THE DEEP SEA 



The cold bottom waters of polar origin are known to be rela- 

 tively high in carbon dioxide, and thus are able to dissolve more 

 of the calcium carbonate. It seems improbable, however, that 

 temperature stratification in the waters could be so marked that 

 this factor alone could account for the sharp limits of the compen- 

 sation depth that have been indicated. Most present consideration 

 of increased solution from hydrostatic pressure does not suggest 

 it as a major factor. It may seem worth additional investigation, 

 however, for with pressures below about 4000 m becoming rather 

 critical, it could explain the sharp limits indicated for the com- 

 pensation depth. 



Other interesting but quantitatively minor biogenous deposits 

 can be mentioned only briefly. 



As indicated, the diatomaceous belt of the North Pacific 

 contains a minor part of diatoms, and lacks the features charac- 

 teristic of pelagic deposits. Diatoms appear to average little more 

 than 10 per cent of this sediment, as indicated by x-ray deter- 

 minations of Goldberg, after converting the opaline silica of the 

 diatoms to cristobalite by heating. Samples from the Antarctic 

 belt are more highly diatomaceous, and in part, at least, show the 

 more oxidized character of typical pelagic sediments. 



The small size and shape of diatoms results in settling rates 

 approximating 50 years or more to reach the bottom, and the more 

 delicate ones are dissolved before reaching the ocean floor. Lateral 

 distribution by currents appears to be less extensive, however, 

 than has been suggested, as indicated by Fig. 7. These unpublished 

 data from Kanaya indicate a few of the characteristic species, 

 among more cosmopolitan ones, that are not mixed in the bottom 

 sediment throughout the Pacific. The indicated distribution from 

 north to south in the Pacific is only from the few samples studied 

 to date. 



The skeletal remains of Radiolaria are a conspicuous element of 

 some pelagic sediment, though seldom amounting to more than 

 about 10 per cent even in the so-called radiolarian ooze. Accumu- 

 lation appears greatest in the equatorial belt of generally high 

 productivity, but they dominate the biogenous component only 

 in the north edge of this belt where solution of calcium carbonate 

 has increased their proportion. Their value in age assignments has 



