Natural and anthropogenic organic matter inputs to intertidal deposits of the urbanized Arctic region: A multi-proxy approach

Abstract Growing anthropogenic activity in the Arctic, especially near regional municipal and transportation hubs, threatens coastal environments with significant changes and contamination. A detailed study of a wide set of organic-geochemical proxies in surface and subsurface sediments and soils around the typical urbanized Arctic area (Tromso, Norway) was performed to investigate natural and anthropogenic input of hydrocarbons. The sites were located close to main areas of human activity and differed in the level of anthropogenic pressure: oil terminal, boat harbor and recreation beach zone in the city center, and a remote, conditionally-clean area. The samples from each site were collected along four subtidal – intertidal – supratidal transects. GC–MS data on the distribution of more than 110 compounds were obtained including n -alkanes, isoprenoids , terpanes, parent polycyclic aromatic hydrocarbons (PAHs), and alkyl PAHs. Organic matter embedded in a mineral matrix was more thermally mature than its fresh non-bound fraction. Biomarker distribution and diagnostic ratios attested to the predominantly local origin of near-shore organic matter formation (phytoplankton, algae, high foliar plants, grass). PAH composition revealed a significant input of pyrogenic components from liquid and solid fuel combustion to the surface coarse-grained sediments. Background bacterial activity was evidenced by the high content of biohopanes and hopenes in less polluted sediments and soils. The presence of an unresolved complex mixture and even n -alkanes in sediment profiles from the most polluted sites attested to the active biodegradation that, together with the erosion of the upper layers by tidal currents , reduces the toxic compound penetration deeper into the sediments.