A 2014 study from the UW documented that the ocean in the region is warming at a depth of 500 meters (0.3 miles), by water that formed decades ago in a global warming hotspot off Siberia and then traveled with ocean currents east across the Pacific Ocean. Methane deposits are abundant on the continental margin of the Pacific Northwest coast. "Current environmental changes in Washington and Oregon are already impacting local biology and fisheries, and these changes would be amplified by the further release of methane," Johnson said.Īnother potential consequence, he said, is the destabilization of seafloor slopes where frozen methane acts as the glue that holds the steep sediment slopes in place. Marine microbes convert the methane into carbon dioxide, producing lower-oxygen, more-acidic conditions in the deeper offshore water, which eventually wells up along the coast and surges into coastal waterways.
But most of the deep-sea methane seems to get consumed during the journey up. If methane bubbles rise all the way to the surface, they enter the atmosphere and act as a powerful greenhouse gas. Of the 168 methane plumes in the new study, some 14 were located at the transition depth - more plumes per unit area than on surrounding parts of the Washington and Oregon seafloor. It is unknown what role it might contribute to contemporary climate change, although recent studies have reported warming-related methane emissions in Arctic permafrost and off the Atlantic coast. Methane has contributed to sudden swings in Earth's climate in the past. "So it is not likely to be just emitted from the sediments this appears to be coming from the decomposition of methane that has been frozen for thousands of years." Paul Johnson, a UW professor of oceanography. "We see an unusually high number of bubble plumes at the depth where methane hydrate would decompose if seawater has warmed," said lead author H. Credit: Brendan Philip/University of Washington The base of the column is 1/3 of a mile (515 meters) deep and the top of the plume is at 1/10 of a mile (180 meters) depth. Sonar image of bubbles rising from the seafloor off the Washington coast.