Organic Constituents 



273 



Deposition of gypsum by replacement or 

 crystal growth has not yet been noted in the 

 California basin sediments, but it has not 

 been carefully sought. Because of losses of 

 hydrogen sulfide from the surface of sedi- 

 ments, we can expect to find that the total 

 sulfur in all forms decreases with depth in 

 the sediment in a fashion similar to that ob- 

 served for total nitrogen. Some of the stages 

 of this regeneration have been observed by 

 Sugawara, Koyama, and Kozawa (1953, 

 1954) in fresh, brackish, and marine sedi- 

 ments of Japan. The cycle is also being 

 studied at the University of Southern Cal- 

 ifornia by I. R. Kaplan, who uses isotopes 

 of sulfur to measure the nature of the 

 changes. 



Regeneration of nutrients from the bottom 

 is minor in comparison with regeneration in 

 the overlying water, amounting to less than 

 1 per cent of the annual requirements of 

 phytoplankton, but this regeneration is an 

 important factor modifying the nature of 

 organic materials that are permanently lost 

 from the ocean by burial in sediments. Evi- 

 dence of the gross eff'ect of regeneration on 

 the sediments is exhibited by the decrease 

 with depth of total nitrogen (Fig. 217), and 

 by probable but unmeasured losses of phos- 

 phate, siUca, and sulfur from organic ma- 

 terials. Losses are especially great in oxi- 

 dizing environments such as those of Santa 

 Catalina Basin where only about one-half 

 the original amount of organic matter sur- 

 vives to a depth of 2 meters, about 8000 

 years. Losses are smaller in the anaerobic 

 environment of Santa Barbara Basin where 

 more than two-thirds survive to the same 

 depth, although its age is only about 600 

 years. The surviving material is more stable 

 and resistant to further change than is that 

 originally deposited. 



Organic Constituents 



General 



Information about the source of organic 

 matter and the biogenic and abiogenic losses 

 that it undergoes before and after reaching 



the bottom have been discussed in previous 

 sections, with the more important stages 

 evaluated in Figure 153. Factors that con- 

 trol the extent and nature of the losses be- 

 tween plant growth and burial of the rem- 

 nant in sediments, such as oxygen content 

 of the water, activity of bacteria and animals, 

 and Eh of the sediments, have also been de- 

 scribed. The percentages of organic matter 

 that occur in bottom sediments of various 

 kinds of areas of the sea floor, such as 

 shelves and basin floors, are summarized in 

 Tables 12 and 14 and Figures 155, 178, 182- 

 1 85, 196, 203, and 204. In addition, the rate 

 of deposition of organic matter in basin sedi- 

 ments based on radiocarbon age determina- 

 tions is presented, with a summary in Tables 

 20 and 21 and Figures 207 and 208. 



Total organic matter usually constitutes 

 less than 1 per cent by dry weight of the 

 sediment on the mainland shelf, island 

 shelves, and bank tops. In the basin and 

 trough sediments it is mostly between 5 and 

 10 per cent. Intermediate values occur on 

 basin slopes and sills and on hills that rise 

 above the general level of the basins and 

 troughs. These relationships were observed 

 long ago by Trask (1931, 1932, Fig. 16) on 

 the basis of about 50 samples and were ex- 

 tended by Revelle and Shepard (1939, Fig. 

 8), who analyzed about 210 additional sam- 

 ples. They are shown in still more detail by 

 the 886 samples of Table 12 that have been 

 plotted in map form for the various areas of 

 detailed study. 



Throughout all previous discussions or- 

 ganic matter was considered in toto, although 

 it is well known to have a complex compo- 

 sition. There are many reasons to suppose 

 that the various constituents have diff^erent 

 resistances to decomposition. Accordingly, 

 a knowledge of the composition of organic 

 matter that has accumulated on the sea floor 

 under various conditions of oxidation and 

 rate of burial should go far toward explain- 

 ing the cause and eff'ect relationship of en- 

 vironment and percentage of organic matter 

 in the sediments. If we are ever to learn how 

 petroleum forms, a knowledge of the effects 

 of environment on the early stages of dia- 



