SECT. 1] THE INFLUENCE OF ORGANISMS ON THE COMPOSITION OF SEA-WATER 53 



Richards and Vacarro (1956) have investigated this relation in a number of 

 basins, using the development of anoxia, shown by the concentration of hydro- 

 gen sulfide, as a criterion of the accumulation of products of organic decomposi- 

 tion. Table IX shows that the expected relation obtains between the stability 

 of the water column at sill depth, the development of anoxic conditions, and 

 the estimated age of the water in the basin. 



Table IX 



Comparison of Stability, Accumulation of Hydrogen Sulfide and Age in 

 Stagnant Basins (after Richards and Vaccaro, 1956) 



B. Seasonal Variation in Vertical Exchange 



Under steady-state conditions the distribution of concentrations provides 

 no information on the rates of the processes on which these concentrations 

 depend. In the previous example a measurement of the rate of production of 

 organic matter was used to introduce the factor of time into the calculations. 

 The coefficient of diffusion could have served this purpose were its value 

 known. Where the equilibria change with the season, the resulting changes in 

 concentration may be employed to evaluate the rates at which the component 

 processes take place. A study of the seasonal exchange of oxygen across the sea 

 surface, made in the Gulf of Maine by Redfield (1948), will serve to illustrate 

 this procedure, and, in addition, provides an example of the use of stoichio- 

 metrical relations in separating changes due to biological and physical processes. 



a. The exchange of oxygen across the sea surface 



The quantity of oxygen dissolved in water beneath the sea surface depends 

 on a balance between the rate at which it is exchanged with the atmosphere 

 and the rate at which it is produced or consumed by biological activity, pro- 

 vided the effects of advection may be neglected. Changes in the quantity of 

 dissolved oxygen, AQo, during the time interval At consequently result from 

 an equilibrium represented by 



AQo = AQn AQe , 



At " At At () 



