Delta 13C hydrocarbon, geochemistry of pore water sediment and physical oceanography (CTD) off the Vesteralen coast, northern Norway

The seepage area is characterised by the presence of gas flares in the water column as revealed by hydro acoustic surveys and elevated methane concentrations of up to 42 nM ca. 5 m above the seafloor.

Pore water analyses of three gravity cores from the seepage area show varying depths of the sulphate-methane-transition zone (SMTZ) between 80 cm and > 250 cm indicating spatially heterogeneous methane ascent. The isotopic composition of methane (d13C from - 40per mil to - 63per mil and d2H from - 191per mil to - 225per mil) and d13C depth profiles of methane and dissolved inorganic carbon show that the hydrocarbons are predominantly of thermogenic origin, consistent with d13C values of C2 to C4 hydrocarbons.