SALINITY, GASES 61 



from sea-water about 34 per cent, of oxygen, 

 varying with the temperature and pressure. 



The solubiHty of these gases is affected by 

 the temperature of the water, the higher the 

 temperature the smaller the quantity of gas 

 absorbed, so that polar waters should, and 

 actually do, contain more dissolved gases 

 than tropical waters. The maximum amount 

 of nitrogen and oxygen found by the " Chal- 

 lenger " was in the Southern Ocean towards 

 the Antarctic, where the water contained 

 23-58 cubic centimetres per litre (or parts per 

 thousand), and the minimum was in the 

 tropical West Pacific, where the water con- 

 tained only 11-85 cc. per litre of the two gases. 

 In the former case oxygen made up 35-01 

 per cent, of the mixture, and in the latter 

 33 11 per cent. In the Norwegian Sea the 

 percentage of oxygen in the mixture varies 

 from 31-0 to 36-7, the average to the north of 

 Icit. 70° N. being 35-64, and to the south of 

 lat. 70° N. 34-96 ; at the surface the mean 

 percentage of oxygen is 35-3, diminishing 

 beneath the surface to 32-5 at 300 fathoms, 

 beyond which depth it remains nearly con- 

 stant. 



Except perhaps for an insignificant quantity 

 of nitrogen derived from the decay of dead 

 organisms, practically all the dissolved oxygen 

 and nitrogen in the ocean has been absorbed 



