PELAGIC SEDIMENTS 353 



In the more productive areas, 100 specimens per cubic meter is 

 near Bradshaw's average down to a depth of 100 m, with rapid 

 decrease at greater depths. This would approximate 10,000 for the 

 total water column above a square meter of ocean floor. With a 

 life cycle or residence time of about one year probable, this 

 indicates deposition of one calcareous test per square centimeter 

 of the bottom per year. This rate would approximate only 1 mm 

 of Globigerina ooze per thousand years. 



This rate of accumulation would be only one-tenth of the 1 cm 

 per thousand years indicated from other evidence as near an 

 average rate of post-Tertiary accumulation, and expectable from 

 rate of supply of calcium by rivers. The approximate balance 

 indicated by saturated waters should be maintained in major part 

 by Globigerina ooze deposition. Even smaller rates would be 

 indicated for most of the North Pacific showing the much smaller 

 standing crop. Solution with no net accumulation occurs over 

 much of this region of 5000 m or more depth. 



Some recent data by Be (1959, p. 80, Table 2) indicates much 

 smaller populations of planktonic Foraminifera in the North 

 Atlantic than Bradshaw shows in the Pacific Ocean. The reverse 

 would be expected from rates of post-Pleistocene accumulation in 

 the two oceans. Differences and inadequacies of sampling methods 

 would not seem to account for the difference that exceeds an order 

 of magnitude of ten. Perhaps the residence time or life cycle is 

 much less than one year, and the accumulation rate thus greater, 

 but this would not affect the great difference indicated for the 

 two oceans. Need for additional data on this problem is evident. 



Over large areas of the ocean, such as that in the equatorial 

 Pacific, calcareous tests (dominantly planktonic Foraminifera) 

 constitute up to more than 80 per cent of the sediment. In this 

 belt of high productivity in the equatorial current and counter- 

 currents, the diatom and radiolarian remains commonly form 

 10% or more. The clay and other inorganic particles are less than 

 10%. This and following considerations indicate that in the more 

 productive areas of the ocean the remains of calcareous organisms 

 have accumulated at rates up to nearly 10 times that of other 

 pelagic sediments. 



Arrhenius' study (1952, p. 192) of the Swedish deep-sea cores in 



