NOAA Methane Seep Study

Within the Cascadia Margin (CM) located off the OR and WA coast at water depths of 500m and less, methane continuously bubbles out of the seafloor at sites known as seeps. As the bubbles rise toward the sea surface, they release methane to the water column where it is consumed by bacteria, but some methane is released, either directly or indirectly, to the atmosphere where it acts as a potent greenhouse gas. Although thousands of seeps have been identified n the CM by their characteristic 'acoustic flare' on ship's sonar, little is known about the regional impact these seeps have on water column biogeochemistry and even the estimates of total methane flux are highly uncertain due to difficulty in empirically relating shipboard acoustic backscatter intensity measured at the sea surface to methane fluxed at the sea floor. To solve both of these problems, we propose to use a small fleet of two-person-portable Autonomous Underwater Vehicles (AUVs) equipped with a combination of dissolved methane sensors and high resolution imaging sonars and current meters to quantify methane fluxes all the way to the source at the sea floor. The AUVs will use advanced algorithms to autonomously search for a seep an then efficiently sample it.