SECT. 2] GASES 315 



and about 50 ^"A atoms per minute from the decay of ^oK. To generate the 

 ''He and ^^A dissolved in the ocean through decay of U and K present in sea- 

 water would take 10** and 10^ i years respectively. The apparent radiocarbon 

 age of deep sea-water (see page 317) gives an upper limit of about 10^ years for 

 the time since equilibration with atmospheric gases has been established. 



Because of its low atomic weight, He escapes from the earth's atmosphere. 

 The small amount present in the atmosphere and the oceans represents the 

 equilibrium between the amount escaping and the amount produced by radio- 

 active decay in the lithosphere and transferred to the atmosphere and ocean. 

 A He-flux from the sea floor, supplying 5% of the He present in the bottom 

 1000 meters of sea-water in 1000 years, would correspond to the amount of He 

 produced from U and Th in a few kilometers of sediments and suboceanic rock. 

 It may be possible, therefore, to detect with reflned measurements a helium 

 gradient in the bottom water of the oceans produced by the escape of helium 

 from beneath the sea floor. 



The situation for argon is much less favorable because of the higher 40^ 

 content of the atmosphere and the higher proportion of the dissolved argon to 

 atmospheric argon. Argon, unlike He, does not escape from the atmosphere 

 and, therefore, 40A produced from ^ok decay has accumulated in the atmos- 

 phere during the lifetime of the earth. At the same time it is more soluble in 

 sea- water than helium. 



4. Carbon Dioxide 



The dissolved CO2 in the ocean and its hydrated forms of molecules or ions 

 constitute a complex system. Equilibrium between these various components 

 is established in sea- water, even though the rate of hydration of CO 2 is a 

 relatively slow chemical reaction, in the sense that its time constant is of the 

 order of seconds or minutes, depending on temperature, pH, and other variables. 

 The rate of uptake of CO 2 by a solution is also known to be slow and dependent 

 on many factors, which makes it difficult to compare results of laboratory 

 experiments with conditions prevailing in nature. If CO2 is added to the 

 atmosphere, as has happened during the past century by the combustion of 

 fossil fuels, part of this added amount will be taken up by the ocean. The 

 partition between the ocean and the atmosphere and the rate of partition are 

 both important quantities because the CO 2 concentration in the atmosphere 

 may very well be a factor in the heat balance of the earth as a whole, and 

 notable amounts of CO 2 have been released into the atmosphere by industrial 

 combustion of fossil fuel. 



However, until a few years ago, virtually nothing was known about the rate 

 of exchange and uptake of CO 2 from the atmosphere into the sea, and estimates 

 of the time constants involved ranged from some 10,000 years to a few days. 

 The discovery of natural radiocarbon has now at least allowed narrowing of this 

 range to a value accurate presumably to about one order of magnitude. 



The British meteorologist, Callendar (1938, 1958), believed that nearly all 



