An unknown amount of methane is fluxing through continental margins, and up to ~5000 gigatons of carbon are stored in icy methane hydrate deposits within their sediment. Sources of this methane include biogenic production, disassociation of the methane hydrate layers, and deep thermogenic sources. Methane is one of a group of carbon species that have been recognized as important greenhouse gases and thus the methane geochemical cycle is important to climate modeling. Only in the past several years has sonar technology been available to rapidly locate and map these submarine methane sources over large areas of the seafloor. The Cascadia margin is of particular interest because the methane is stored within the accretionary wedge of a major subduction zone. It represents a geologic end member that has a strong tectonic overprint, in contrast to the thickly sedimented passive margins represented in the U.S. Atlantic and Gulf of Mexico, which also have extensive methane seeps. There is increasing evidence for accumulation of seep-derived carbon species both from known seeps and in regional surface water along the Cascadia margin, which potentially has an environmental impact on the upper water column. A baseline characterization of methane seeps along the Cascadia margin is critical to complete to assess methane input into the water column, and is timely because the continued rise in ocean temperatures could potentially impact the rate of release of methane from the hydrate layers into the ocean and possibly the atmosphere.

For more information, visit EOI's Cascadia Margin pages.