FACTORS CONTROLLING C0 2 IN OCEANS AND ATMOSPHERE 35 



to surface water. Oxygen would show the reverse effect because it is being 

 consumed rather than manufactured in the deep sea. The enrichment around the 

 deep ocean from Atlantic to Pacific results from the fact that the major source 

 of deep water in the world ocean today is at the north end of the Atlantic. Water 

 is being pushed around to the Pacific, and it tends to add to the vertical gradient 

 of chemical properties a horizontal gradient giving the deep Pacific the highest 

 concentration. The horizontal gradient builds up until "leakage" via eddies and 

 minor currents matches the export by the main deep current. The main way in 

 which carbon gets out of the ocean is with these organic particles, although this 

 matter is, to a very large extent destroyed, about 1% gets into the sediment and 

 is lost. Some of this carbon leaves as kerogen (~10%); the rest is removed from 

 the ocean in the form of calcium carbonate. About 85% of the CaC03 produced 

 in the sea is destroyed in the deep sea by dissolution, and about 15% is buried in 

 the sediments. For organic tissue about 99% is destroyed, and only 1% becomes 

 kerogen. 



The decrease between deep and surface ocean is most dramatic for the 

 nutrient elements phosphorus and nitrogen. They drop off by a very large factor 

 and leave a residue in the surface ocean of only a few percent of the deep-water 

 value. Silica is also greatly reduced in concentration through the action of 

 diatoms which, given enough silica, would probably take over the aquatic plant 

 world. By comparison the decrease for total dissolved carbon is only 15% and 

 for calcium (a constituent of calcium carbonate), only about 1%. This results 

 from the fact that, when deep water upwells to the surface, the life forces there 

 quickly combine the critical nutrients, nitrogen and phosphorus, into organic 

 matter. To do so requires one hundred or so carbon atoms for each phosphorus 

 atom. Some of these organisms also need calcium carbonate to house themselves. 

 One group of plants called coccoliths makes little calcite cages, and, of course, 

 many of the animal plankton make calcium carbonate shells. As far as we know, 

 for every hundred units of carbon in surface water which falls as organic tissue, 

 30 units fall as calcium carbonate. The amount of carbon going into organic 

 tissue is dictated by the amount of phosphorus and by the normal chemical 

 composition of plant matter (Fig. 3). This composition is pretty much the same 

 through all fresh or marine aquatic organisms and seems to be a fundamental 

 constant of life. 



The silica goes into opal, some of which is produced by plants and some by 

 animals that house themselves in opal instead of calcium carbonate. They use 

 whatever silica is available along with the necessary amount of nitrogen and 

 phosphorus. When silica runs out, the rest of the nitrogen and phosphorus, as 

 well as that recycled within the surface sea, is used by other organisms. I will 

 attempt to show that it is the economics of these elements that control the 

 oceanic (and hence atmospheric) carbon cycle. 



Carbon has a residence time in the ocean of only about a hundred thousand 

 years. That means that every hundred thousand years we have had a completely 



