GEOLOGY. 333 



There is also greater evaporation. Taken together, these give to the mean 

 surficial influence of the ocean a cooHng rather than a warming influence.^ 



But when the accumulation and retention of heat within the great body 

 of the ocean, and their bearings on climatic eras of the geologic order, are 

 considered, the case assumes an aspect of a high order of importance. 



The surface of the ocean is about three times that of the land, but the 

 oceanic mass subject to climatic changes is probably twenty or thirty times 

 that of the surface film of the land which partakes effectively in climatic 

 changes. Besides, the specific heat of water is about five times that of 

 average soil or rock. These differences give to the ocean a capacity for storing 

 heat which is a high multiple of that of the land or that of the atmosphere. 

 It is a thermal reservoir of vast competence. The atmosphere serves as a 

 door of entrance into this and exit from it, much as the nitrogen group, in a 

 smaller way, forms a reservoir to which carbon dioxide and water-vapor serve 

 as doors of entrance and exit. 



The very massiveness of the ocean and its exceptional capacity for heat 

 make its responses to external changes in the heating process very slow and 

 the time-factor rises to special importance. 



The three well-known agencies of oceanic circulation give rise to cycles of 

 three orders of time values: (1) cycles due to propulsion by wind; (2) cycles 

 due to heating in low latitudes and to coohng in high latitudes; (3) cycles due 

 to increase of salinity in zones of high evaporation and to freshening in zones 

 of high precipitation. 



(1) The first is a direct atmospheric contribution and is effective chiefly 

 in giving surficial and regional currents with incidental upwellings and 

 sinkings. The periods of these cycles are long relative to those of the atmos- 

 pheric cycles, but short relative to those of the deep-sea circulation. 



(2) The cycles due to heating in low latitudes and cooling in high latitudes, 

 if they were permitted to work alone, would give rise to vertical circulation 

 involving a surficial and a deep-sea component. Its periods would quite 

 certainly be much longer than the preceding, but as the case is purely hypo- 

 thetical this need not be urged. 



(3) Cycles due solely to increase of salinity in areas of descending air, and 

 consequent evaporation, cooperating with freshening in areas of ascending air 

 and precipitation. If this couplet could act alone, its period would also be long. 



The actual deep-sea circulation is the joint product of temperature differ- 

 ences and salinity differences acting as basal agencies, the wind contributing 

 a surficial influence. Since circulation is an effort to secure equilibrium 

 between disturbing causes, this degree of complexity of causes prolongs the 

 effort and obscures the result, but gives it all the more climatic significance, 

 for it is nature's correlation between the two greatest of the atmosphere's 

 dynamic factors, differences in latitudinal heating and in vertical heating, 

 both expressing themselves in part by the latitudinal winds and by vertical 

 circulation of the atmosphere, which actuates evaporation and condensation. 



The single method thus far proposed for the measurement of the cycle of 

 this complex circulation rests upon the rate at which the combination of icy 

 cold and highly saline water — of the type that fills the abyssal basins of the 

 ocean — is formed in the polar regions. This is theoretically correlated 

 with an atmospheric cycle of carbon dioxide, and subordinately of oxygen, 

 for the assigned formation of the abyssal type of cold saline water is a side 



^ A venerable climatic fallacy, Jour. Geol., vol. xxxi, pp. 179-191 (April-May 1923). 



