Composition of shelf methane seeps on the Cascadia Continental Margin
Article first published online: 31 MAR 2005
Copyright 2005 by the American Geophysical Union.
Geophysical Research Letters
Volume 32, Issue 6, March 2005
How to Cite
2005), Composition of shelf methane seeps on the Cascadia Continental Margin, Geophys. Res. Lett., 32, L06609, doi:10.1029/2004GL022050., and (
- Issue published online: 31 MAR 2005
- Article first published online: 31 MAR 2005
- Manuscript Accepted: 28 FEB 2005
- Manuscript Revised: 18 FEB 2005
- Manuscript Received: 22 NOV 2004
 Methane reservoirs and seeps are an active component of the continental margin carbon budget and represent a poorly characterized pathway for reduced carbon cycling and methane input to the atmosphere. Active gas seeps from three shelf settings on the Cascadia Continental Margin off Oregon and Northern California contain nearly pure methane with a heavy carbon isotope composition (−29 to −35‰). An extensive study of the gas seep at Coquille Bank, Oregon, revealed a warm, buoyant pore fluid associated with the pockmark. As methane enters the water column above these seeps in a steady gas stream, a fraction escapes directly to the atmosphere while the balance dissolves into local seawater. Measured oxidation rates are too slow for significant local oxidation within the water column near the seep. Large mats of pink and white bacteria, including Beggiatoa spp. are found around the vent, demonstrating the activity of sulfide oxidizers in this ecosystem.