Escape of methane gas through sediment waves in a large methane hydrate province

doi:10.1130/0091-7613(2002)030<0467:EOMGTS>2.0.CO;2

Escape of methane gas through sediment waves in a large methane hydrate province

¹Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA
²School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
³Institute for Geophysics, University of Texas, Austin, Texas 78759–8345, USA
⁴Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA

Abstract

Despite paleoceanographic evidence that large quantities of methane have escaped from marine gas hydrates into the oceans, the sites and mechanisms of methane release remain largely speculative. New seismic data from the Blake Ridge, a hydrate-bearing drift deposit in the western Atlantic, show clear evidence for methane release and suggest a new mechanism by which methane gas can escape, without thermal or mechanical disruption of the hydrate-bearing layer. Rapid, post–2.5 Ma formation of large sediment waves and associated seafloor erosion created permeable pathways connecting free gas to the seafloor, allowing methane gas expulsion. The amount of missing methane, 0.6 Gt, is equivalent to ∼12% of total present-day atmospheric methane. Our results imply that significant amounts of methane gas can bypass the hydrate stability zone and escape into the ocean. Mechanisms of tapping methane directly from the free-gas zone, such as widespread seafloor erosion, should be considered when seeking the causes of large negative carbon isotope excursions in the geological record.