314 REVELLE AND SUESS [CHAP. 7 



a gas sample extracted from ocean water taken at 5350 meters depth halfway 

 between Hawaii and Christmas Island (14° 12'N, 155° 08' W) in the Pacific 

 Ocean. 



2. Oxygen and Nitrogen 



The oxygen content is one of the most characteristic quantities of an oceanic 

 mass and varies between the rather large limits of 2 to 8 milliliters/liter. These 

 variations, on which an extensive literature exists, are due to biological activity, 

 viz. photosynthesis and bacterial oxidation of organic matter. A summary of 

 present ideas is given by Richards (1957). 



The most interesting feature of the O2 distribution in the oceans is the 

 occurrence of an oxygen minimum at intermediate depth, and its quantitative 

 explanation includes unsolved oceanographic problems. The amounts of dis- 

 solved nitrogen are far less accurately investigated. According to Rakestraw 

 and Emmel (1938) these amounts show only minor variations. In general the 

 nitrogen concentration should correspond to its solubility, although effects 

 from biological activity may be expected locally. 



3. Rare Gases 



The rare gases dissolved in the oceans have not yet been investigated in 

 detail. Because of their chemical inertness, their concentration should correspond 

 approximately to their solubilities at the respective water temperatures. 

 However, the temperature dependence of solubility is relatively large and is 

 greatest in the case of Xe which is more than twice as soluble in water at 0°C 

 than at 25°C (Morrison and Johnstone, 1954). Heat transfer through the ocean 

 surface by conductivity and radiation is presumably considerably faster than 

 transfer and equilibration of atmospheric gases, and, therefore, one might 

 expect appreciable deviations from equilibrium concentrations. Mass-spectro- 

 scopic isotope-dilution techniques now make it possible to determine small 

 quantities of rare gases accurately to within 1% without too much effort, so 

 that such measurements may provide new possibilities to study the ocean- 

 atmosphere interchange of gases and transfer phenomena. Even more sig- 

 nificantly, the mixing of water masses of different temperatures might be 

 determined by accurate measurements of the variations in the xenon/neon 

 ratio, taking advantage of the fact that the temperature coefficient for solubility 

 of xenon is not linear with temperature. By comparison of the xenon con- 

 centration with that of helium in the bottom water (see below) the amount of 

 heating of this water by heat from the earth's interior and hence its "age" 

 could be independently determined and an estimate could be made of the rate 

 of escape of helium from the crust and mantle. 



The rare gas isotopes "^He and ^^A are produced by radioactive decay. The 

 amounts produced, however, are small. In one liter of sea-water about 30 He 

 atoms per minute are produced from the decay of uranium and its daughters, 



