Temporal variability of in situ methane concentrations in gas hydrate-bearing sediments near Bullseye Vent, Northern Cascadia Margin
Article first published online: 30 JUL 2013
©2013. American Geophysical Union. All Rights Reserved.
Geochemistry, Geophysics, Geosystems
Volume 14, Issue 7, pages 2445–2459, July 2013
How to Cite
2013), Temporal variability of in situ methane concentrations in gas hydrate-bearing sediments near Bullseye Vent, Northern Cascadia Margin, Geochem. Geophys. Geosyst., 14, 2445–2459, doi:10.1002/ggge.20167., , , , and (
- Issue published online: 3 SEP 2013
- Article first published online: 30 JUL 2013
- Accepted manuscript online: 14 MAY 2013 04:09AM EST
- Manuscript Accepted: 2 MAY 2013
- Manuscript Revised: 25 APR 2013
- Manuscript Received: 10 OCT 2012
- gas hydrates;
- carbon stable isotopes;
 To assess the temporal variability in the methane fluxes from marine sediments that overly gas hydrate bearing sediments and the factors that might control its rate, in situ methane concentrations were measured near Bullseye Vent on the Northern Cascadia continental margin. A long-term sampling device collected overlying water and pore-fluid samples from 25 cm above seafloor, at the sediment-water interface (SWI), and 7 cmbsf (centimeters below seafloor) over a 9 month period (August 2009–May 2010). These samples provide a record at ∼4 day resolution of in situ methane, ethane, propane, sulfate, and chloride concentrations, as well as stable carbon isotope ratios of methane (δ13C-CH4) and dissolved inorganic carbon (δ13C-DIC). We show that pore fluids near the SWI are saturated or supersaturated with respect to methane (∼80 mM) and the methane flux from the seabed is variable over time. We hypothesized that regional seismic activity controlled this variable CH4 flux in the Northern Cascadia continental margin setting. However, we found no direct correlation between earthquakes and CH4 flux. We also posited alternative controls on CH4 flux variability, such as storms, regional oceanography and microbial activity. Again, no direct correlation was seen. This study takes first steps toward exploring which physical factors play a role in methane flux from hydrate-bearing sediments.