2000). Both the present study and that of Yunker et al. (1996) identified BKF as a dominant PAH in Barents Sea sediment deposits (Table 3). This compound is not produced commercially on an industrial scale (Lide (ed.) 1991) but enters the environment as a by-product of the incomplete combustion of organic material. PHE, the predominant PAH at the northern stations (III and VIII), is also a combustion by-product. Hence, the PAH composition at all stations exhibits an anthropogenic signature consistent with known industrial activities in the region. In contrast, check details Boitsov et al. (2009b) reported a predominance of alkylated PAHs in sediments collected from the western Barents Sea: an indication of petrogenic PAHs.

However, we are unable to compare their results with ours because in the present investigation we did not measure alkylated compounds. To assess the origin of PAH contamination of sediments, we use individual component ratios as a diagnostic tool (Budzinski et al. 1997, Qiao et al. 2006). Since we ITF2357 were not able to measure lighter alkylated PAHs, only FLT/PYR, PHE/ANT and CHR/BAA indices are presented. Compound ratios of FLT/PYR > 1, PHE/ANT < 10 and CHR/BAA < 1 are characteristic of pyrolytic sources of PAH, while FLT/PYR < 1, PHE/ANT

> 15 and CHR/BAA > 1 indicate PAHs of petrogenic origin (Dahle et al. 2003). At the four stations investigated, FLT/PYR > 1 and PHE/ANT < 10 (Figure 3) are consistent with the conclusion that PAHs are of pyrogenic origin, e.g. coal combustion. At station VIII, the PHE/ANT

ratio (9–15) was relatively high compared to the other stations (3–10). This feature is explained as resulting from mixed pyrogenic and petrogenic origins, a finding that is consistent with the sediment mixing reported earlier. Boitsov et al. (2009b) report PHE/ANT ratios (from 9.4 to 113) for 69 stations in the western Barents Sea. As previously mentioned, these authors detected petrogenic PAHs with only minimal influence from anthropogenic sources. The difference between our conclusion and that of Boitsov et al. (2009b) regarding the origin of PAHs is most likely due to local differences in mixing regimes. The sediments collected CHIR-99021 mw for this study were mostly mixed in the surface intervals; hence, modern sediments were contaminated by the signatures laid down in previous decades. There is a general pattern of increasing PHE/ANT ratios with sediment depth/deposition time (Figure 3). This pattern reflects the down-core transition from anthropogenic to natural hydrocarbon sources over time from the present day to the pre-industrial period. Polychlorinated biphenyls were detected in sediments down to 4 cm depth. Concentrations of ∑7 PCB within this depth interval ranged from 0.7 ± 0.3 ng g−1 to 3.5 ± 1.4 ng g−1 (Table 2), with the highest concentration detected at station III and the lowest one at station I. 7 PCB inventories in the uppermost sections of the cores (0–4 cm) were lower (1.0 ± 0.4 ng cm−2–1.2 ± 0.