Cost-effective and relocatable monitoring of hydrocarbon seepage in offshore environments.

Hydrocarbon seepage is overlooked in the marine environment, mostly due to the lack of high-resolution exploration data. This contribution is about the geophysical and geochemical investigation of two seepage sites on the shelf of the Adriatic Sea: an oil spill off Civitanova Marche, at water depth of 10 m; scattered biogenic seeps offshore Mt. Conero, at water depth of 84 m. The accurate detection of gas plumes was achieved with a multibeam system acquisition of the water column reflectivity. Dissolved benthic fluxes of nutrients, metals and DIC were measured by in situ deployment of a benthic chamber, which was used also for the first time as water samples collector for hydrocarbons gas characterization. In addition, concentration of Polycyclic Aromatic Hydrocarbons and major and trace elements was analyzed to provide an estimate of hydrocarbon contamination in the surrounding sediment.