600 KAPLAN AND RITTENBERG [CHAP. 23 



life in the ocean has been more or less constant over long periods, indicate 

 that steadj'-state conditions exist. 



Under steady-state conditions as much nitrogen, ])hospliorus and silicon 

 must be deposited annually in sediments, or otherwise lost from the ocean, as 

 is contributed to the ocean from non-marine sources. Total fixed nitrogen is 

 contributed in far greater quantity than is lost to sediments; maintenance of 

 balance can be attributed to denitrification. On the other hand, both phosphorus 

 and silicon are brought to the ocean and deposited on its floor in approximate 

 balance. Because the contribution of each is dominantly in the form of mineral 

 grains, the j^ercentages of phosphorus and silicon in the ocean-bottom sedi- 

 ments are not materially different from their percentages in stream-borne 

 sediment. 



Comparative studies of the early diagenetic processes in sediments of the 

 Santa Barbara, Santa Monica and Santa Catalina Basins have been made 

 (Emery and Rittenberg, 1952; Rittenberg, Emery and Orr, 1955). The first is 

 highly reducing with free hydrogen sulfide in the interstitial water, the second 

 is mildly reducing with no free H2S and the third is oxidizing at the surface 

 and reducing below a depth of about 200 cm. The variation of nitrogen com- 

 pounds in these sediments is shown in Fig. 4. Although the cumulative content 

 does not vary appreciably in the surface sediments of the three basins, the 

 dominant species is different in each, as is the change with depth. The existing 

 patterns are understandable in terms of environments and the biochemistry of 

 the bacterial processes involved. 



Ammonia, which results from deamination of amino acids (proteins) and other 

 organic constituents, can be produced under both aerobic and anaerobic condi- 

 tions by a large variety of organisms. Bacterial deamination continues down to 

 a depth of over 400 cm (representing several thousand years since the time of 

 deposition), as can be judged from the increase of ammonia with depth. The 

 increase is most noticeable in the reducing basin since here losses occur only 

 by diffusion upward into the overlying water. 



In the presence of molecular oxygen, ammonia is oxidized first to nitrite and 

 then to nitrate by the Nitrosomonas and Nitrobader groups respectively. An 

 oxidized environment should, therefore, contain nitrate and this is precisely 

 what is found in the Santa Catalina Basin sediments. Here nitrate forms to 

 considerable depths as it probably also does in certain sandy layers of the Santa 

 Monica Basin sediments introduced by turbidity currents. 



Nitrate, like ammonia, can be lost from the sediment by diffusion into the 

 overlying w^ater. In addition, the conversion of nitrate to molecular nitrogen 

 (denitrification) can occm\ Laboratory investigations have shown that de- 

 nitrification can take place only in the absence of molecular oxygen. The recent 

 field data of Richards and Benson (1959), who demonstrated by measurements 

 of the i^N/i^N ratios in molecular nitrogen from the bottom waters of Cariaco 

 Trench and Oslo fjord that biological nitrogen is liberated in the anaerobic 

 environment only, are in agreement. In Santa Catalina Basin nitrate formed in 

 the upper zone of oxidized sediment can be denitrified in the reduced sub- 



