FACTORS CONTROLLING CO, IN OCEANS AND ATMOSPHERE 



41 



100 



80 



O 

 O 



CJ 



60 — 



40 



20 











1 



2 3 4 5 



DEPTH IN SEDIMENT, m 

 Fig. 5 Calcium carbonate as a function of depth in a sediment core from western flank of 

 East Pacific Rise. 



suspect that, when the compensation level was very shallow, calcium carbonate 

 in sediments would be subjected on the average to a greater degree of dissolution 

 than when the compensation level was deeper and the degree of solution less. We 

 can look at different sediment columns for variations in the extent of 

 dissolution. 



One of the most interesting indicators of paleochemistry in the ocean is the 

 C to C ratio in the calcium carbonate that is being deposited. There is a 



1 ^ 



2 per mil higher C content in the dissolved carbon in warm surface water than 

 there is in deep Pacific water, and, as is often the case, the Atlantic water falls 

 roughly halfway between. The reason for this pattern is that the organic material 

 being produced in this surface water is depleted in ' C by 20 per mil by 

 photosynthetic fractionation. It is leaving behind in the surface water carbon 

 enriched in C; the carbon that is carried down by mixing has to carry away 

 more C than the carbon that comes up in order to balance the fact that the 

 carbon going out with the particles is deficient in l C. Calcium carbonate does 

 not fractionate the carbon isotopes so that it does not alter the isotope ratio 

 upon formation or dissolution. Roughly three-fourths of the particulate carbon 

 is going down in the form or organic carbon (fractionated), and the other 

 one-fourth is going down in the form of calcium carbonate (unfractionated). 



