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

• Main Authors: Sauer, Simone, Knies, Jochen, Lepland, Aivo, Chand, S, Eichinger, Florian, Schubert, Carsten J
• Format: Other/Unknown Material
• Language: English
• Published: PANGAEA 2017
• Subjects: Northern Norway
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.876596; https://doi.org/10.1594/PANGAEA.876596

We investigated active methane seeps in a water depth of 200 m in the Hola area off the coast of Vesteralen, northern Norway, to assess (1) hydrocarbon sources, (2) migration pathways and (3) the influence of hydrocarbon seepage on sediment pore water and water column chemistry. 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. Isotope data also indicate considerable biodegradation of propane. Seismic profiles from the study area reveal major faults and steeply dipping unconformities between the basement and overlying Mesozoic sedimentary rocks. We propose that these act as migration pathways for the hydrocarbons from late Jurassic to early Cretaceous source rocks.