ZoBell 



— 20 



Marine Microbiology 



CO2 is produced by the respiration of all organisms and is utilized by 

 photosynthetic and chemosynthetic organisms. The CO2 in the atmos- 

 phere is in equilibrium with that in the ocean. Minute changes in the pH 

 of the oceans of the world would materially alter the CO2 content of the 

 atmosphere. 



The dissolved oxygen content of sea water is a function of temperature, 

 pressure, salinity, and biological activity. When in equilibrium with the 

 atmosphere at 760 mm. pressure at 15° C, sea water having a salinity of 

 34.325°/oo contains 5.86 ml. or 8.40 mgm. of oxygen per liter. The solu- 

 bility of oxygen increases with decreasing temperature and it increases 

 with decreasing salinity. Oxygen is consumed by respiring organisms in- 

 cluding bacteria. In sea water and bottom deposits bacteria probably 

 consume more oxygen than all other organisms combined, depleting the 

 oxygen in certain localized regions. Photosynthetic organisms produce 

 oxygen, sometimes in sufficient amounts to supersaturate the water in 

 the euphotic zone. 



125 



100 



&0 6.5 7.0 7.5 8.0 8.5 90 



pH 



Fig. I . — ■ Effect of />H on the relative concentrations of free CO2, HCOa", CO3 , 

 and total CO2 in sea water {adapted from Moberg et al., 1934). 



Below the euphotic zone the oxygen content of sea water usually de- 

 creases vertically to a depth of 600 to 900 meters, the so-called oxygen 

 minimum layer, and then increases again towards the bottom. The 

 oxygen content of sea water at depths exceeding 1000 meters is deter- 

 mined primarily by its past history, origin, or movements, because there 

 are not enough organisms present at such depths to have much effect 

 until the sea floor is reached. Little or no dissolved oxygen is found in 

 bottom deposits and the juxtaposed water. 



Dissolved nitrogen is of little biological importance in the sea. Small 

 quantities may be utilized by nitrogen-fixing bacteria and some is liber- 

 ated by the activities of denitrifying bacteria, but it has not been demon- 



