Dataset for: “Temporal variability of in situ methane concentrations in gas hydrate-bearing sediments near Bullseye Vent, Northern Cascadia Margin”

Methane concentrations were measured in gas hydrate-bearing sediments near Bullseye Vent, Northern Cascadia Margin from August 7, 2009 to May 14, 2010 using a long-term sampling device to determine temporal variability. Overlying water and pore-fluid samples were collected from 25 cm above seafloor, at the sediment-water interface, and 7 cm below seafloor (cmbsf). Concentrations of in situ methane, ethane, propane, sulfate, chloride, stable carbon isotope ratios of methane (δ13C-CH4), and dissolved inorganic carbon (δ13C –DIC) were measured.