rate indicates the rate at which the carbon is being contributed to 
the deep water -- a possible consideration when interpreting the cl 
(18) 
dating results. 
Minimal Turnover Rate from Phosphorus Cycle: The quantity 
of phosphorus in the oceans is known within better than 50 percent. 
There are estimates of the productivity of the surface layers of 
the ocean, given in terms of carbon, but which can be converted into 
units of phosphorus. If ail the phosphorus went through the life 
cycle, and was incorporated into plants when it came from the deep 
water, it would take about 500 years for all of the phosphorus in 
the oceans to pass through the productive layers once. This estimate 
gives an idea of the minimal turnover time because there is a great 
(26) 
deal of recycling of phosphorus near the surface. 
-60- 
