The study is an early step toward exploring the release of methane from estuaries, or places where saltwater and freshwater meet, a subject more widely studied in Europe. Credit: Paul Johnson/University of Washington 25, 2020, about 1 mile offshore from Seattle’s Alki Point. This research video shows bubbles emerging from the seafloor about 200 meters (650 feet) deep. There’s occasionally a burst of bubbles, and then another one 50 feet away that has a new burst of bubbles.” “There are holes all over the place, but there aren’t bubbles or fluid coming out of all of them. “Off Alki, every 3 feet or so there’s a crisp, sharp hole in the seafloor that’s 3-5 inches in diameter,” Johnson said. At Alki, the bubbles rise 200 meters, about the height of the Space Needle, to reach the ocean’s surface. Methane plumes were seen from Hood Canal to offshore of Everett to south of the Tacoma Narrows. Since then, the team analyzed sonar data collected during 18 cruises on the UW’s smaller research vessel, the RV Rachel Carson. The underwater images created by the soundwaves showed a distinct, persistent bubble plumes as the vessel rounded the Kingston ferry terminal. Thompson, had kept its sonar beams turned on as it returned to its home port on the UW campus. The bubbles in Puget Sound were first discovered by surprise in 2011, when the UW’s global research vessel, the RV Thomas G. Previous UW research had found methane bubbling up from the outer coasts of Washington and Oregon. “Single plumes are all over the place, but the big clusters of plumes are at Kingston and at Alki Point.” “There’s methane plumes all over Puget Sound,” said lead author Paul Johnson, a UW professor of oceanography. The columns of bubbles are especially pronounced off Alki Point in West Seattle and near the ferry terminal in Kingston, Washington, according to a study in the January issue of Geochemistry, Geophysics, Geosystems. Black squares are urban sewer outfalls, which don’t match the bubble plumes’ locations. Black lines show the South Whidbey Island Fault Zone, the Seattle Fault Zone and the Tacoma Fault Zone. This map of Puget Sound shows the location of the methane plumes (yellow and white circles) detected along the ship’s path (purple).
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