SECT. 3] BASIN SEDIMENTATION AND DIAGENESIS 599 



that in the Black Sea bottom waters and sediments the bacterial counts were 

 higher than in the North Pacific. Not only were anaerobes numerous, but nitri- 

 fying bacteria, thiobacteria and aerobic protein decomposers were also isolated 

 in large numbers. According to Kriss, life in the bottom waters of the Black 

 Sea consists primarily, if not exclusively, of bacteria, and the average bacterial 

 biomass was 1.5 to 2 times that of the oxygenated zone. As a consequence of the 

 large volume of the Black Sea containing hydrogen sulfide, the total biomass 

 there is estimated as 18.5 x 10^ tons as compared with 17.7 x 10® tons in the 

 oxygenated and euphotic zones. 



Care must be exercised in interpreting data pertaining to reported bacterial 

 poj^ulations and types. All counts based on culture procedures have the limita- 

 tion that only those types capable of development under the nutritional and 

 physical environment imposed by the experimenter will be counted, and the 

 diversity of bacteria is such that only an undeterminable and probably small 

 fraction of a complex population is enumerated in any single procedure. Direct 

 microscopic techniques not only involve technical difficulties, especially when 

 dealing with sediments, but also fail to distinguish between living and dead 

 organisms. More important, the detection or counting of a particular type by 

 any technique does not establish its significance in the environment in which it 

 is found. Many kinds of bacteria, for example nitrifiers or sulfate reducers, can 

 be detected in appreciable numbers in environments in which they cannot be 

 active, at least insofar as we understand their physiology and metabolism. Much 

 more attention must be paid to the development of methods that will enable 

 quantitative assessment of the in situ activity of the different groups of 

 bacteria. 



c. Nutrient regeneration 



Perhaps the most vital role performed by bacteria on the ocean bottom is 

 that of mineralization, the regeneration of nutrients previously fixed by other 

 living systems. This occurs throughout the entire water column as well as in the 

 unconsolidated sediments, but is most effective in, or just below, the photo- 

 synthetic zone (Riley, 1951) where the plankton content is highest and death 

 is proportionally high, and at the mud-water interface where the dead organisms 

 come to rest. The net result is a solution of the soluble inorganic ions by the 

 deep-ocean waters which are then returned to the euphotic zone by upwelling. 

 A survey of the nutrient budget for the world's oceans by Emery, Orr and 

 Rittenberg (1955) indicates that far more nutrients were annually assimilated 

 by xolankton than were supplied by the major sources. The renewal times (the 

 number of years that would be required for dissolved nutrients in rivers, plus 

 rain in the case of nitrogen, to build up the nutrients dissolved in the ocean 

 water to their present concentrations in the absence of withdrawal) are similar — 

 12,000, 60,000 and 27,000 years for nitrogen, phosphorus and sihcon, respect- 

 ively. All are close to the renewal time for the water itself, 50,000 years (volume 

 of ocean divided by annual volume of river flow). The brevity of these renewal 

 times and the character of the geological record, which suggests that the total 



