2.1 Sediments and Sediment Cores (Extraction and Processing) 



Samples of surface sediment or specific depth interval sections of 

 sediment cores were solvent-extracted and fractionated according to an 

 ambient temperature solvent drying and solvent extraction procedure 

 based on that of Brown et al. (1980) as revised by Atlas et al. (1981) 

 and Boehm et al. (1981). The procedure, involving methanol drying and 

 ambient temperature extraction with a methylene chloride/methanol 

 azeotrope, is illustrated in Figure 2.1. The concentrated extract is 

 displaced with hexane and charged to a glass absorption chromatography 

 column (1 cm i.d.) containing 10 g fully activated (150°C) 80-100 mesh 

 silica gel topped with 1 g 5% deactivated alumina and 1 g activated 

 (i.e. acid washed) copper powder. The column, which is wet packed in 

 methylene chloride, is rinsed with this solvent followed by hexane. A 

 0.5 ml volume of extract is charged to the column and eluted with 

 hexane (17 ml, f]_) » hexane: methylene chloride (21 ml, f 2) , and 

 methanol (20 ml, f 3) . The fractions are collected separately, reduced 

 in volume, desulfurized using an activated (1 N HC1) copper powder 

 slurry, and an aliquot weighed on a Cahn electrobalance. The f^ and 

 f2 fractions are then analyzed by fused silica capillary gas chroma- 

 tography (FSCGC flame ionization detector) and a selected set further 

 scrutinized by gas chromatographic mass spectrometry. FSCGC analysis 

 determined the overall composition of the sample by appraisal of the 

 distribution of resolved (peaks) and unresolved (hump) features, 

 as well as the specific quantities of individual n-alkane (C^g to C32) 

 and isoprenoid (C15 to C20) compounds. GC/MS/computer analyses focused 

 on the list of saturated and aromatic compounds presented in Table 2 to 

 confirm the identities of compounds or to quantify minor, but important 

 "marker" compounds. 



Details of the GC and GC/MS analytical procedures are presented in 

 Table 3. 



Quantification of GC traces was according to the internal standard 

 method wherein quantities of individual hydrocarbons are computed. 

 Several other GC-derived parameters were routinely calculated on sample 

 data. One of these was the n-alkane to isoprenoid ratio (ALK/ISO) in 

 the C13 - C19 range: 



ArK/Tsn = n ~ C 14 + "-Cis + n-Ci e. + n C, 7 + n-Ci a 



' 1380 + 1450 + 1650 + 1710 + 1812 a 



a GC retention indices of isoprenoids: 1450 = farnesane, 1710 = 

 pristane, 1812 = phytane. 



This ratio, beginning at ^7 in the reference oil is quickly 

 decreased due to preferential bacterial degradation of n-alkanes 

 versus the branched isoprenoids. 



The carbon preference index (CPI) , the ratio of odd chain alkanes 

 to even chain alkanes in the n-C26 to n-c 31 range, is defined as 

 follows: 



2(n-C ?7 + n-Coq) 



CPI = n-C 26 '+ 2n-C 2 Q + n-C 30 



38 



