Variability of present and past PAH concentrations in sediments of the SW Barents Sea

Abstract

The concentration and distribution of polyaromatic hydrocarbons (PAHs) in surface and subsurface sediment samples from Tromsøflaket and Ingøydjupet, southwestern Barents Sea, were investigated in order to provide insight into the levels and origins of PAHs in a region with petroleum activities. PAH profiles in sediments were evaluated in context with sediment grain size and total organic carbon in order to assess the influence of ocean currents on the transportation and deposition of PAHs. The PAH concentrations are of background (Level I) to good level (Level II) based on the Water Framework Directive classification system. SUM PAH (SUM of 26 PAH compounds) ranged from 39 to 2197 µg/kg (average 225 µg/kg), and NPD (naphthalene, phenanthrene and dibenzothiophene, including their C1–C3 alkyl homologues) in surface samples ranged from 14 to 2045 µg/kg (average 157 µg/kg). However, the average values presented here are higher than have been reported in previous studies. The observed changes in PAH contents in surface and subsurface sediments vary in accordance with changes in grain size (clay and silt 17–99%) and total organic carbon content (0.37–0.98%). In turn, these sedimentary parameters are controlled by the inflow of Atlantic Water and the strength of the two predominating current systems in this region: the North Atlantic Current and Norwegian Coastal Current. Source-allocation modeling suggests that PAHs in surface samples are mainly of pyrogenic or mixed pyrogenic and petrogenic origin. Taken together, these patterns of PAH levels and sources reflect natural variability, indicating that the derived dataset establishes a pre-impacted baseline of the present state of the seafloor.