Organic Constituents 



275 



Figure 221. Variation of the 

 state of oxidation of organic 

 matter with depth in basin 

 sediments. From Emery and 

 Rittenberg (1952, Fig. 25). 



basin sediments by comparing the results of 

 organic carbon analyses by wet combustion 

 and by an empirical titration method. The 

 top sections of twelve cores (Fig. 221) had 

 an average content of organic carbon 2 per 

 cent lower when determined by titration than 

 by combustion, whereas at 3 meters the av- 

 erage was 1 1 per cent higher. These differ- 

 ences indicate that organic carbon near the 

 sediment surface is in a slightly higher state 

 of oxidation, and at depth it is in a lower 

 state than in average soil for which the 

 method was calibrated by Schollenberger 

 (1927) and Alhson (1935). Thus a larger 

 amount of reagent is required to oxidize the 

 carbon at depth than nearer the surface. Be- 

 cause of the various uncertainties, no par- 

 ticular ratio of total organic matter to 

 organic carbon can be accepted as correct; 

 however, for the sake of consistency the fac- 

 tor 1.7 has been used throughout the work 

 on southern California sediments. 



Analyses for organic carbon by combus- 

 tion are time consuming, and analyses by 

 titration are subject to error because of un- 

 certainty of the state of oxidation for any 

 particular sample; accordingly, many analy- 

 ses have been made by the rapid and accu- 

 rate Kjeldahl method for another measure 



of total organic matter, nitrogen. In using 

 this measure, however, we must remember 

 that the ratios of carbon to nitrogen and of 

 total organic matter to nitrogen are not fixed. 

 In fact, their variations provide some infor- 

 mation about the history of the organic 

 matter. Easiest to determine is of course 

 the C/N ratio. 



Some of the first workers to make much 

 use of the C/N ratio were Trask and his as- 

 sociates, using a titration method for organic 

 carbon. Trask's (1932) average for 86 sam- 

 ples from the region off" southern California 

 was 8.3 and for 13 surface samples from 

 basin floors 8.0. A plot of carbon versus 

 nitrogen for 79 samples from 13 later basin 

 cores (Fig. 222) shows a higher ratio, aver- 

 aging about 12.2. However, this average is 

 complicated by the presence of at least two 

 variables: (1) some samples are from near 

 the surface (mostly shallower than 35 cm) 

 and some are from depth (mostly between 

 275 and 325 cm), and (2) the carbon of some 

 samples was determined by wet combustion 

 but for most it was by titration which is 

 known to depend on the state of oxidation 

 which changes at depth. Based on only the 

 more reliable combustion carbons, the C/N 

 ratios of the surface samples average 11.3 



