Sources, dispersal pathways and mass budget of sedimentary polycyclic aromatic hydrocarbons (PAH) in the NW Mediterranean margin, Gulf of Lions

Polycyclic aromatic hydrocarbons (PAH) were investigated in surface sediments from the river-impacted Gulf of Lions shelf and slope (NW Mediterranean), with the aim to comprehensively assess their occurrence, sources and dispersion pathways and to provide reliable estimates on their accumulation fluxes and budget. Elevated concentrations were found in the prodeltaic zone, albeit less important than in other coastal systems worldwide under enhanced human-made pressure. Mixed sources, pyrolytic and petrogenic, occur at varying contributions, depending on point-sources and transport mechanisms. Predominant pyrolytic PAH accumulate in the deltaic area, via fast settling of organic-rich riverine clays. Both preferential particle associations and sediment dynamics were found to control their dispersal pathways from point-sources, while a diffuse petrogenic signature is evidenced on the shelf. Total PAH inputs are estimated at 12.42 T year− 1, from which 10.8 T year− 1 are derived from the Rhône River alone. The major part (9.3 T year− 1) is sequestered on the shelf, which acts as a key sink for particle-bound PAH. Yet, off-shelf export of PAH through submarine canyons toward the slope and open sea is significant (ca. 21% of the total input). The findings provide sound insight into the behavior, fate and budget of PAH in the sensitive zone of the Gulf of Lions shelf and slope that can be viewed as a showcase for river-impacted continental shelves under human-made pressures.