184 REPORTS ON INVESTIGATIONS AND PROJECTS. 



In this way it is possible that at times when the atmosphere was 

 relatively rich in carbon dioxide the ocean was relatively poor in 

 the same constituent. The supply of carbonates, which was a con- 

 trolling factor, was measurably dependent upon the ratio between 

 the exposure of the land surface to atmospheric contact on the one 

 hand and the conditions for the extraction of the carbonates fur- 

 nished particularly by the epicontinental seas on the other. The 

 variation in these relations is believed to have at times favored the 

 enrichment of the ocean in carbonates, and at other times its deple- 

 tion, and hence to have changed the basis of equilibrium with the 

 atmosphere. 



In the study of the interchange between the carbon dioxide of the 

 ocean and of the atmosphere, it appeared that direct diffusion was but 

 feebly competent, because of its slowness of action, and, further, 

 that the mechanical intermixture of atmosphere and ocean through 

 wave and current action was too superficial to more than moderately 

 supplement the feebleness of diffusion. The familiar ocean currents 

 appear to be essentially superficial, and probably do not greatly assist 

 in the interchange between the carbon dioxide of the atmosphere and 

 that of the great abysmal body of the ocean. It is clear, however, 

 that there is now a profound circulation of a different and much 

 slower type, which affects this abysmal body and in the course of a 

 long period exposes it at the surface. This profound circulation at 

 present is actuated by the low temperature and the concentration of 

 salinity arising from the freezing of the surface water in the polar 

 regions. To this profound circulation must apparently be assigned 

 the task of changing the state of carbonation of the great body of 

 the oceanic waters so far as it is dependent on interchange with the 

 atmosphere. When the deep-sea circulation has its present phase, 

 i. c, when the waters descend in the polar regions, move thence 

 toward the Equator, rise in the low latitudes, and thence return 

 superficially to the polar regions, it tends to carbonate the deep 

 waters of the ocean to a degree higher than that of the average state 

 of equilibrium between the ocean and the atmosphere, because the 

 coefficient of absorption of carbon dioxide for the low temperatures 

 of the polar regions is roundly double that of waters at the equatorial 

 temperatures and much higher than that at average temperatures. 

 The result is that the deeper body of the ocean is cold and somewhat 

 supercarbonated relatively to the average atmospheric state. This 

 appears to find expression in the solution of carbonates which is now 

 prevalent in the depths of the sea. This tendency to supercarbona- 

 tion is intensified by the freezing of the surface waters in the polar 



