46 



PHOTOSYNTHESIS 



is a cap or belt of air of low carbon dioxide-content at the poles of the 

 earth. The mixing of a portion of this mass of cold air is supposed to be 

 intimately associated with formation of cyclones. It might be expected 

 therefore that the passage of a "low"' would give some indication in the 

 carbon dioxide-content of the air. Some evidence of this is claimed by 

 Lundegardh,*® though a clear demonstration thereof is made difificult on 

 account of the influence of other factors. 



The carbon dioxide-content of the sea and atmosphere represents a 

 dynamic equilibrium. There are, on the one hand, sources which are 

 producing carbon dioxide in prodigious quantities and, on the other hand, 

 agents which are removing the carbon dioxide from air and sea. The 

 nature of these sources and agents differs widely. The situation can be 

 schematically represented about as follows : 



CO, PRODUCTION 



Springs 



Volcanoes 



Combustion of Coal, 



Wood and Petroleum \ 

 Respiration of lower 



organisms, plants 



and animals 



-> Atmosphere and Sea 



CO2 CONSUMPTION 



Photosynthesis by 



Plants 

 CaCOs-forming 



organisms 

 - Chemosynthesis of 



certain bacteria 

 The weathering of 



rocks 



It is not possible to discuss here exhaustively all the factors which 

 effect this equilibrium. We are dealing with chemical changes taking 

 place on an enormous scale and in many cases involving extensive periods 

 of time. Nor are we probably familiar with all the factors which have 

 a part in this great drama in which the life of man plays but an insignificant 

 role. For this reason most calculations are but rough approximations. 



Let us consider first the sources of carbon dioxide. What may be 

 termed the inorganic sources are perhaps of the greatest influence. Thus, 

 there are ancient craters (e.g. Agnano near Naples) and gas wells which 

 have been discharging carbon dioxide since time immemorial. The 

 composition of the gases of volcanic eruptions varies greatly but carbon 

 dioxide is a frequent component.*^ The observations of Lewy ^° on the 

 island of Guadaloup, though not very accurate, indicate that after the erup- 

 tion of the volcano the atmosphere contained fifty times the normal amount 

 of carbon dioxide. No consistent efforts have been made to determine 

 whether the great volcanic disturbances result in changes in the atmospheric 

 carbon dioxide-content at distances from the place of eruption. Even less 

 is known concerning the volcanic eruptions at the bottom of the sea. Min- 

 eral springs constitute a very important source of carbon dioxide ; the 

 waters of some of them are supersaturated with the gas as they issue 



*' Lundcgardh, Der Krcislauf der Kohlcnslhire. p. 38. 



"Allen, E. T. J., Franklin Inst., 193, 29 (1922) for bibliography and chemical 

 analyses of volcanic gases. 



''Lewy, M., Ann. Chim. Phys., 8, 425 (1843). 



