Just as the ALK/ISO ratio describes the chromatographic composition 



of the ii— C , „ to n-C 10 range, the carbon preference index (CPI) describes 

 i j io 



the nature of the n-C , to n-C or . range. Aikanes within this range can 



Zo jL) 



indicate a petrogenic input (CPI = 1.0) or, as the CPI increases above 1, 

 it documents an increased input of terrigenous n-alkanes having their 

 source in vascular plant waxes (Farrington and Meyers, 1975). With 

 increasing time, the hydrocarbon material sedimented in the region more 

 closely reflects these normal terrigenous inputs (Table 11.5), thus 

 illustrating that direct petroleum deposition appears to occur only 

 during the early post-spill period, perhaps on the order of to 3 

 weeks. Thereafter, it is possible that deposition continues outside of 

 the three station transects due to the slick movement. 



The changes in the character of the aromatic hydrocarbon composi- 

 tion of the trap material are illustrated in Fig. 11.7 and 11.8. The GC 

 profiles of the aromatic composition (Fig. 11.7) indicate that the 

 amount of the resolved material decreases relative to the whole oil and, 

 as was the case with the aliphatics, the UCM achieves a chromatographic 

 significance. This was observed in the November Macoma and December 

 Mytilus GC profiles as well. However, unlike the aliphatic hydrocarbon 

 changes which appear to be microbially mediated, changes in the aro- 

 matics appear to depend on solubility considerations, the lower boiling 

 compounds being preferentially lost. 



The total amount of resolved material decreases rapidly (Tables 

 11.5 and 11.6). However, on a comparative basis, consider Fig. 11.8 

 which, like the corresponding consideration of the Mytilus and Macoma 

 data, indicates preferential loss of the soluble naphthalenes, biphenyl , 

 and fluorene compounds, and soon thereafter the dibenzothiophene parent 

 compound (see also Table 11.6). Microbial activity would result instead 

 in loss of or conversion of the methyl side chains in the various homo- 

 logous series. The composition of the aromatic hydrocarbons in the 

 traps is severely altered by the third week after the spill and consists 

 mainly of the phenanthrene series and substituted dibenzothiophenes . 



247 



