a Location of investigated sites off the western Svalbard margin. Background bathymetry from IBCAO55 (gray); higher resolution bathymetry from UiT—The Arctic University of Norway database. The distribution of surveyed gas plumes during yearly expeditions to the area is indicated by green circles. Pockmarks without associated gas plumes on the western Vestnesa Ridge are indicated as gray dots. Shaded areas over the bathymetry correspond to mapped bottom simulating reflectors56. b Station PZM1 is located within the gas hydrate stability area and near a sediment depression where gas hydrates have been recovered37. c PZM2 was deployed in an area characterized by a seismic facies showing parallel reflections and no major vertical discontinuity.