ZoBell — 106 — Marine Microbiology 



teria influence the Eh of the medium in which they are growing; the Eh of 

 the medium has a pronounced effect on the multiphcation and metabolism 

 of bacteria (see extensive reviews of Hterature by Elema, 1932; Hewitt, 

 1936; and Kanel, 1941). For example, sulfate reduction, denitrification 

 (Elema et al., 1934; Korochkina, 1936), and the reductive deaminization 

 of amino acids are enhanced by a relatively low Eh, whereas the oxida- 

 tion of carbohydrates to CO2 and water is favored by positive Eh values. 

 Whether acids, alcohols, or other products result from the fermentation 

 of carbohydrates has been shown by Kusnetzow (1931) to be partly a 

 function of the Eh of the medium. 



The redox potentaal of sea water is primarily a function of its oxygen 

 content. Cooper (1937a) iound the redox potential of normal surface sea 

 water to be near Eh + 0.4R volt, increasing as the pH decreases. This 

 value compares favorably with Eh + 0.46 to 0.50 volt found by Hutchin- 

 son et al. (1939) in oxygenatM lake water. Somewhat lower values were 

 found in shallow inland seas by Kusnetzow (1935a). 



The redox potential of lake muds examined by Kusnetzow (1935&) 

 ranged from Eh + o. 145 to — o. 142 volt. In Wisconsin lakes Allgeier et al. 

 (1941) found Eh values ranging from +0.512 volt in upper oxygenated 

 water to — 0.140 volt in bottom deposits. Finding marked differences in 

 the redox potentials on different dates led them to conclude that the poten- 

 tials are controlled by dynamic factors that are in a state of flux, and not 

 by static agents. Bacteria or their metabolic products are probably the 

 responsible agents in the hypolimnion and in bottom deposits. 



In brown bottom deposits from the Barents and Kara Sea which con- 

 tained appreciable quantities of iron and manganese, Brujevicz (1937, 

 1938) found the Eh to range from + 0.105 to 0.250 volt. In black mud 

 rich in H2S, one might expect the conditions to be reducing. 



Several hundred potentiometric measurements made on profile sam- 

 ples of bottom deposits from the Pacific Ocean show that, as a rule, the 

 redox potential decreases with jdepth. Except under water containing 

 H2S, the redox potential of th^ sediments at the mud-water interface 

 ranges from Eh o or slightly pos]|tive values to Eh — 0.2 volt. The redox 

 potential decreases more or less regularly with depth to a depth of 25 to 

 50 cm. where the Eh is - 0.2 to - 0.4 volt. At greater depths the re- 

 sults have been somewhat erratic, fluctuating from Eh — 0.2 to — 0.5 volt 

 at pa 7.0. One sample gave a reading of Eh — 0.58 volt, this being the 

 most reducing sediment examined. Bacterial cultures observed in the 

 laboratory are able to create such reducing conditions, and unquestion- 

 ably are at least partly responsible for the reducing conditions found in 

 bottom deposits (ZoBell, 1939a). 



The erratic results obtained at core depths exceeding 25 to 50 cm. are 

 attributed partly to technical difficulties involved in making the measure- 

 ments on freshly collected samples and partly to the decrease in the content 

 of reversibly oxidizable or reducing constituents. The poising capacity, as 

 indicated by the quantity of reducing substances in the sediments, usually 

 decreases with core depth. This is shown by the data in Table XXX 

 which gives the oxygen-absorbing capacity (spontaneous or abiogenic) of 

 samples from different core depths. 



The redox potential has a marked influence upon the direction, velocity, 

 and magnitude of chemical reactions which involve the exchange of elec- 

 trons, or the oxidation or reduction of reactants. Consequently, the redox 

 potential probably influences the diagenesis of bottom deposits in many 



