FACTORS CONTROLLING CO, IN OCEANS AND ATMOSPHERE 



45 



3.1 



E 



3.5 



O 



CD 



X 



Q. 

 LU 



Q 3.9 



4.3 



140 132 124 116 



LONGITUDE, °W 

 Fig. 7 The percent of calcite above and below the compensation level. 



reduction in the planktonic-to-benthic ratio during interglacial times than 

 during glacial times. In the Caribbean Sea the calcite component, which is the 

 main component of the CaC0 3 , is not dissolved during either period, but, in the 

 glacial part of the section, aragonitic pterapods are found. Aragonitic calcium 

 carbonate, which is a metastable, is 1.6 times more soluble than calcite. In 

 today's Caribbean the pterapod shells that fall to the bottom are dissolving. 

 During the peak of the last glacial period, pterapods accumulated in the 

 Caribbean in great numbers, suggesting again that at the peak of the glacial 

 period the compensation depth was deeper, subjecting the sediments to less 

 solution. It is not clear why this happened. There are many possible 

 explanations. For example, when the sea level went down during the glacial 

 period, it cut off a tremendous amount of near-shore CaC03 production. The 

 wide shelves were laid bare, and, of course, the calcium carbonate removed from 

 the system on the shelves would have been cut way back. 



A logical thing to do is to run an "uphill" traverse of cores right across this 

 compensation level and look directly at the differences between cores from 

 above the compensation level to cores below. Our geophysicists at Lamont once 

 ran such a traverse for heat-flow study and got closely spaced cores on a traverse 

 east from Tahiti to the crest of the East Pacific Rise about 17 south. We had 

 been studying those cores and found a very dramatic thing; the cores down to 

 about 3950 m are about 90% calcium carbonate; the cores below 3950 m are, on 



