THE PERMIAN PERIOD. 667 



removed, as well as half of that in the air; hence the slowness of permanent 

 changes in the carbon dioxide of the air. But this theoretical conclusion is 

 qualified by the rates of diffusion of carbon dioxide in sea-water. The rate of 

 this diffusion has not been experimentally determined, but supposing it to be 

 as high as other rates of diffusion that have been determined, it would require 

 millions of years for any notable percentage of the above restorative action to 

 take place, and the completion, or even closely approximate completion, of the 

 whole process would apparently require more than the lapse of known geologic 

 history. 1 This, be it noted, is on the assumption of quiescent waters when 

 diffusion acts alone. 



The influence of agitation and circulation. — Agitation, combined with diffu- 

 sion, accelerates the process, indeed, its efficiency is practically dependent on 

 the surface agitation and on the circulation of the ocean. The agitation of the 

 ocean is quite superficial, and the more conspicuous part of its circulation is 

 also superficial. Now it is in this superficial, sunlit part that nearly all the plants 

 of the ocean live, feeding upon carbon dioxide and setting oxygen free. This is 

 partly, but not wholly offset, by the animal life in the same horizon, for observation 

 shows that it is relatively low in carbon dioxide and high in oxygen. It is this 

 inherently impoverished layer, especially affected by organic action, that is 

 subject to agitation in contact with the air. This layer intervenes between 

 the great bodies of the air and of the ocean that are but slightly affected by local 

 organic action and between which the chief equilibrium exchange must take 

 place, if it takes place at all. The diffusion which directly affects the body of 

 the ocean is that between the superficial layer impoverished by plant action, 

 and the great mass of waters below. If the matter were pursued into detail, 

 it would be found that the state of carbonation of the superficial part of the 

 ocean, and its interchange of carbon dioxide with the air above and the great 

 body of the ocean below, are subject to much variation in different parts and 

 different seasons; but upon this we cannot here erlter. 



That portion of the oceanic circulation which is most concerned in the car- 

 bonic equilibration of the air and ocean, is the deep circulation which now is 

 initiated in the polar regions by reason of their low temperature. As this is a 

 function of temperature, it brings us to the second qualification of the tendency 

 to equilibrium. 



The influence of temperature. — The coefficient of absorption of carbon dioxide 

 in sea-water increases rapidly as the temperature is lowered, the rate being 

 doubled for about 21° C, lowering 2 in the vicinity of 0° C. At present, the tem- 

 perature of sea-water, in passing from the equatorial regions, where it rises 

 from the depths, in the abysmal circulation, to the polar regions, where it descends, 

 experiences a reduction of several degrees more than 21° C, and hence, if the air 

 and ocean were in carbonic equilibrium at the equator, they would be far out 



1 This statement is based on a mathematical inspection by A. C. Lunn. For an 

 analogous application of the rate of diffusion to lavas see Pecker, Am. Jour. Sci. Ill, 

 1897, pp. 27-29. 



2 Krogh, loc. cit. pp. 363-365. 



