June 12 - 29: PMEL scientists with the Earth-Ocean Interactions (EOI) Program will join the E/V Nautilus to continue to survey methane sites from Northern California to Washington using multibeam sonar and a remotely operated vehicle in order to fully document and characterize this region. Up until a few years ago, only 100 methane “seep sites” had been identified primarily by fisherman using their fish-finders observing the acoustic reflections of the gas bubbles.  Beginning in 2016, EOI scientists began a more systematic mapping of the seeps using new sonar technology on the E/V Nautilus, owned and operated by the Ocean Exploration Trust.  About 25 percent of the potential methane seep water column area has now been mapped and analyzed.

During the day, a remotely operated vehicle (ROV) will collect samples of gas, methane hydrate, seep water, fauna and rocks at these sites.  Analyzing these samples in conjunction with a more complete inventory of sites will help scientists understand the origin of the seeping methane and its impact on the ocean environment. At night, the Nautilus will continue to survey additional methane sites.

The Cascadia margin is of particular interest because the methane is stored within a major subduction zone which can potentially have 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.

During the expedition, ROV dive video will be available live at: https://nautiluslive.org/

More information about the methane research and expedition can be found at: https://www.pmel.noaa.gov/eoi/pmel-theme/methane-seeps