August 26, 2014
Newly Discovery Atlantic Methane Vents Could Pose Global Warming Threat
redOrbit Staff & Wire Reports - Your Universe Online
Geologists from Mississippi State University, Brown University, the US Geological Survey (USGS) and Maryland-based Earth Resources Technology, Inc. have discovered more than 500 bubbling methane vents on the seafloor of the northern part of the US Atlantic margin, various media outlets reported on Sunday.
Their research, published online Sunday in the journal Nature Geoscience, suggests that these seeps might be emitting as much as 90 tons of greenhouse gases every year. If there are more of these vents – and the scientists predict that there might be up to 30,000 of them worldwide – they could represent a previously unknown source of environmentally harmful CO2 emissions.
“The bubble streams showed up on sonar scans of the sea floor taken between September 2011 and August 2013 during oceanographic expeditions ranging from Cape Hatteras in North Carolina to Georges Bank off Cape Cod,” explained Scientific American reporter Sid Perkins. The authors said they have analyzed data covering a 94,000 square kilometer arc of land, and discovered the 570 seeps in an area of approximately 950 kilometers.
Co-author and Mississippi State geologist Adam Skarke told Perkins that the number was astonishing, given how few scientists had detected in the region up to that point. While some of the plumes extended hundreds of meters above the ocean floor, Skarke (formerly a physical scientist with the NOAA) said that bubbles originating from deep-water sources typically become dissolved in the sea water well before they would be able to reach the surface.
He and his colleagues report they have not yet collected samples of the bubbles produced by the seeps, but USGS geophysicist Carolyn Ruppel told Perkins that the team presumes that they contain methane because many of them exist in areas that had once been methane-producing wetlands before becoming submerged. Studying those bubbles and the waters surrounding the plumes will help experts estimate the impact of the emissions.
The gas reacts to and diminishes dissolved oxygen, and this process creates carbon dioxide that will cause the waters in and around the vents to become more acidic, the researchers explained to Scientific American. Ronald Cohen, a geologist at the Carnegie Institution for Science in Washington DC who was not involved in the study, said that the study was “very careful” and “lays the groundwork for further research” in the field.
“It is the first time we have seen this level of seepage outside the Arctic that is not associated with features like oil or gas reservoirs or active tectonic margins,” Skarke told BBC News environmental correspondent Matt McGrath. “The methane is dissolving into the ocean at depths of hundreds of meters and being oxidized to CO2. But it is important to say we simply don't have any evidence in this paper to suggest that any carbon coming from these seeps is entering the atmosphere.”
Skarke and his colleagues believe that many of these newly discovered seeps could be related to the breakdown of a frozen combination of methane in sediments below 500 meters of ocean water. This gas hydrate, also known as “methane ice,” can release its methane into the sediments with slight changes in ocean temperature, the researchers explained in a statement. This would allow the gas to escape at the seafloor to form plumes in the water column.
The study authors told BBC News that they estimate there might be 30,000 of these seeps worldwide, but admit that this is an unconfirmed calculation. These vents might not pose an immediate global warming threat, they explained, but if they are correct about the number of them, it could force climate scientists to revisit existing calculations on the potential sources of greenhouse gases, McGrath explained.
Skarke said the research “does not provide sufficient evidence to draw objective conclusions about the relationship between these methane seeps and global climate change.” However, he added that the discovery “introduces a number of related questions that require further exploration and investigation to address.”
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