ZoBell — 168 — Marine Microbiology 



Regeneration of phosphate : — Phosphorus occurs in organisms pri- 

 marily in the form of phospholipids and nucleoproteins. Animal bones 

 consist largely of tricalcium phosphate. Most organic phosphorus com- 

 pounds seem to be very susceptible to decomposition by bacteria. Phos- 

 phate is liberated very early in the process. 



In experiments conducted by Seiwell and Seiwell (1938), about half 

 of the phosphorus content of freshly collected zooplankton was decom- 

 posed in 24 hours after the death of the zooplankton, whereas oxygen con- 

 sumption by bacteria in the experiments indicated that half of the total 

 organic content of the zooplankton was not oxidized for four or five days. 

 In similar experiments conducted by Cooper (1935), about one-fourth to 

 one-third of the phosphorus content of marine zooplankton was liberated 

 as phosphate during the first twelve hours of bacterial activity and nearly 

 all of it in six days. Phosphate was liberated from phytoplankton some- 

 what less rapidly. 



The rapid regeneration of phosphate from dead bacterial cells was ob- 

 served by Renn (1937a). He reported that after bacterial growth had 

 passed its maximum in sea water enriched with phosphate and glucose, the 

 regeneration of phosphate followed "almost at once — rapid at first, and 

 then leveling off at 14 days toward completion." Phosphate was not Hb- 

 erated from autolyzing, bacteria-free diatoms. 



There has been considerable speculation regarding the place of phos- 

 phate regeneration. The occurrence of a far greater concentration of 

 phosphate in deep water than near the surface has been interpreted by 

 some oceanographers as indicating that phosphate is regenerated on the 

 sea floor. While unquestionably a certain amount of phosphate is regen- 

 erated in bottom deposits, the foregoing observations on the rapidity of 

 phosphate regeneration, together with other considerations, strongly sug- 

 gest that the majority of the phosphorus cycle is enacted in the euphotic 

 zone. There large quantities of phosphate may be regenerated, but phos- 

 phate may not accumulate because it is utilized by phytoplankton or 

 bacteria almost as rapidly as it is regenerated. 



From their studies on the rate of sinking of decomposing plankton, 

 Seiwell and Seiwell (1938) concluded that due to the low density of the 

 great mass of organic material, most bacterial decomposition must occur 

 in the upper levels of the ocean. Significantly, they found that the min- 

 imum concentration of oxygen occurs in the western North Atlantic basin 

 in water which has a density value somewheie near that of the great mass 

 of organic matter, namely, 1.027,232 ± 0.000,008. This suggests that 

 most organic decomposition and hence phosphate regeneration takes place 

 above the oxygen minimum layer, roughly 600 to 800 meters. Below this 

 depth only denser, particulate organic matter, which constitutes only a 

 small fraction of the total organic content of the sea, sinks. This is in 

 agreement with the observations of Rakestraw (1936), who noted that 

 the zone of maximum accumulation of phosphate roughly parallels that of 

 nitrite. 



Similar conclusions were reached by Redfield (1942) who believes that 

 the phosphate maximum and oxygen minimum in the North Atlantic are 

 ascribable to the oxidation of organic matter within a few hundred meters 

 of the surface. While part of the phosphate content of South Atlantic 

 water at mid-depths may be derived from the isentropic movement of 

 subsurface layers from higher latitudes, in equatorial and North Atlantic 

 regions, phosphate may be added and oxygen removed by the decomposi- 



