Gas hydrates and active mud volcanism on the South Shetland Trench, Antarctic Peninsula

During the Antarctic summer 2003–2004, new geophysical data were acquired aboard R/V OGS Explora in the BSR area discovered in 1996–1997 along the South Shetland continental margin, Antarctic Peninsula. The objective of the program was to verify the existence of a potential gas hydrate reservoir and to reconstruct the tectonic setting of the margin, controlling extent and character of the diffused and discontinuous bottom simulating reflections. The new dataset, multibeam bathymetry, seismic profiles, and gravitycores, analysed by computer-aided tomography and for gas composition and content, clearly shows active mud volcanism sustained by hydrocarbon venting: several vents, located mainly close to mud volcanoes, were imaged during the cruise and their occurrence identified in the sediment samples. Mud volcanoes, vents and recent slides border the gas hydrate reservoir. The cores are composed of stiff silty mud. In core GC01, collected close to a mud volcano ridge, the following gases were identified (maximum contents in brackets): methane (46 μg/kg), pentane (45), ethane (35), propane (34), hexane (29) and butane (28). In core GC02, collected on the flank of the Vualt mud volcano, the corresponding data are methane (0 μg/kg), pentane (45), ethane (22), propane (0), hexane (27) and butane (25).