42 PHOTOSYNTHESIS 



the oxygen-content is equal to that of sea-water in equihbrium with air. 

 In Tal)lc 4 are given the results of one of Schulz's analyses. By "relative 

 oxygen-content" is meant the ratio in per cent of sea-water in equilibrium 

 with air to the amounts actually found. 



In the winter the conditions are changed ; due to cooling, convection 

 currents are set up which result in more thorough mixing of the water. 

 The changes throughout the year are, however, greatly affected by local 



conditions.^^ . 



There is a slight increase in the amount of free carbonic acid in sea- 

 water with depth though there is apparently no invert ratio between the 

 oxygen-content and that of carbon dioxide. The quantitative relation of 

 these two gases is of great importance to the life of plants and animals in 

 the sea and the relative content in the sea is probably to a considerable 

 extent also determined by the activity of plants and animals. 



TABLE 5=" 



Average Amount of Free Carbonic Acid in Sea-water at Various Depths in 



MG. PER Liter. 



c,,rfare 42.6 300 fathoms 44.0 



25 fathom;-::::::::.: 33.7 4oo ;; 41.0 



CO " 48.8 800 " 42.2 



^00 " ' ' 43.6 More than 800 fathoms 44.6 



200 " :::::: 44.6 Bottom 47.4 



One of the most striking properties of sea-water is the constancy of 

 its hydrogen ion concentration. Thus Politzsch *» found that in samples 

 of water taken from the Atlantic, the Mediterranean, the Black Sea and the 

 Baltic the hydrogen ion concentration varied only from IQ-^'^^ to IQr^-^^. 

 Atkins*' has made determinations of the hydrogen ion concentration of 

 sea-water over several years and found that the changes in the pH values 

 are associated with a variety of factors but that the variations are very 

 ' small. The variations in pH are somewhat greater where there is abundant 

 plant and animal life, as near the coast. Photosynthesis causes the water 

 to become more alkaline, while the carbon dioxide liberated in respira- 

 tion tends to decrease the alkalinity. Where large streams meet the sea 

 the water may, of course, vary in composition. Also in some regions 

 sulphurous acid is found in the lower depths of the sea which naturally 

 increases the hydrogen ion concentration in that locality. 



McClendon *' and his collaborators have made a careful study of hydro- 

 gen ion concentration and carbon dioxide-content of sea-water. They 

 conclude that the pH of sea-water is determined "solely by the ratio of 

 the concentration of bufifers, including carbon dioxide and other weak 



'" Schulz, Arch, deutsch. Seewarte, 41, 8 (1923). 

 •'"From Clarke, Data of Geochemistry (1924), p. 146. 

 '"Politzsch, S., Biochem. Zeit., 37, 116 (1911). 



"Atkins W. R. G.. Journ. Marine Biol. Ass., 12, 717-771 (1922), 13, 93-118 

 (1923), 13,' 437-446 (1924). 



"McClendon, Carnegie Inst, of Washington, Pub. No. 251, 23-69 (1917). 



