FIGURE 3.58. AMC-4 sediment cores. 



DECEMBER 1979 



IPHC 



C30BT 



AUGUST 1979 |NEW .NPUTl 



NOVEMBER '979 



SM 



AMOCO CADIZ OIL 



PYflOGENIC 



BIOGENIC 



o-s 



8-13 R 



IPMC C3P 202i^g 31 



lpg'91 C3O6T 



cores, Figures 3.59 to 3.62 the AMC-4 cores and Figure 3.64 a L'Aber 

 Ildut core. Most of the cores were subdivided into sections of 3-5 cm 

 in depth. However, two finer subdivisions from L'Aber Wrac'h - Novem- 

 ber 1979 (1 cm segments down to 5 cm) , lie Grande - May 1980 (top 10 mm 

 subdivided plus 1 cm sections down to 5 cm) were made. 



Penetration of oil was observed down to 10-15 cm in L'Aber Wrac'h 

 sediments with concentrations decreasing with depth when viewed in 5 cm 

 sections. Note however, that while petroleum aromatics were decreasing 

 in concentration with depth, the pyrogenic PAH compounds increased with 

 depth. Finer subdivisions of the core indicate greater variation 

 within the core than the 5 cm sections would indicate (Fig. 3.52). 



An increase in vertical penetration of oil was observed for the 

 lie Grande site between December 1978 and March 1979. A fresher layer 

 of oil is found at the 15-20 cm depth (see Figs. 3.53 and 3.54) where 

 naphthalenes, dibenzothiophenes, and to a lesser extent phenanthrenes, 

 are more abundant than in surrounding layers. The gross hydrocarbon 

 concentration changes at this level are not nearly as dramatic as are 

 the petroleum aromatics, thus confirming that the "bulge" in Figure 

 3.42 is due to the less weathered nature of the buried oil. The finely 

 divided May 1980 core (Fig. 3.52) indicates a higher petroleum content 

 probably owing to a secondary input or to sampling variability which 

 resulted in much higher levels (5-10 parts per thousand) during May 

 1980. The down core distribution of hydrocarbons is quite non-uniform 

 as well with a preserved layer of fresher oil at 3-4 cm. 



77 



