Sources and distribution of organic matter and polycyclic aromatic hydrocarbons in sediments of the southwestern Portuguese shelf

Total organic carbon (C_org), total nitrogen (N_tot), C_org/N_tot, δ¹³C_org, δ¹⁵N, calcium carbonate (CaCO₃), and grain size were analyzed in 70 surface samples and 19 short cores from the southwestern Portuguese shelf. Perylene and USEPA-16 PAHs were quantified in a subset of these samples. The findings suggest that organic matter derives from a mix of terrestrial and marine sources, outlined by C_org, N_tot, and isotopic signatures. Perylene combined with δ¹³C_org was used to identify the main PAH sources in these environments. Diagnostic perylene ratios revealed contributions from natural sources in the Tagus region and contaminated materials from the Sado Dredged Disposal Site, with additional perylene in Sines linked to atmospheric deposition of pyrogenic sources. A significant correlation between perylene and USEPA-16 PAHs indicates natural and anthropogenic inputs from the Tagus. This multiproxy approach—combining USEPA-16ΣPAHs, perylene, and δ¹³C_org—offers insights for assessing environmental risks and guiding marine environmental management according to the MSFD.