PHASE PHENOMENA 



IN THE CALCITE-SEAWATER SYSTEM 



ROBERT C. COOKE 



Department of Oceanography. Dalhousie University, Halifax, Nova Scotia 



ABSTRACT 



The movement of calcite from its source of production in surface waters to its point of 

 retention in the sediment is affected by both chemical and physical factors. Experiments in 

 which both pressure and composition were varied in the calcite— seawater system show that 

 definite stability boundaries exist and that the lysocline is at least partly a function of the 

 presence of magnesium in both solid calcite and seawater. The concentrations of calcium 

 and magnesium in seawater, or its salinity, also determine the pressure beyond which calcite 

 must dissolve and the composition of the solid calcite required for it to be in steady state in 

 the sea. 



The flux of carbon dioxide in and out of marine sediments occurs in three 

 stages. The first stage is the mass transport of the gas through the boundary layer 

 at the sea surface and the associated processes of hydration and ionization. The 

 second stage is the incorporation of the resultant carbonate into the hard and 

 soft parts of plants and animals by biochemical means and the subsequent 

 release of this material by decay and disintegration. The third is the race 

 between sedimentation and dissolution of the calcite and aragonite produced by 

 organisms in the waters above the sediment. This paper concerns itself with the 

 flux of carbon dioxide to the sediments as carbonate minerals and from the 

 sediments as dissolved carbonate salts. 



The distribution of calcium carbonate in the sediments could be explained as 

 a function of primary productivity and current patterns if the carbonates were 

 carried directly to the sediment by currents and gravity. This is not the case (see 

 references of Arrhenius, 1 Bramlette, 2 Turekian, 3 Cloud, 4 and others) because 

 the solubility of both calcite and aragonite is dependent upon temperature, 

 salinity, depth, and circulation pattern. I will attempt to describe several of these 

 factors in relation to the carbonate system and solid calcite and will then 



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