Environment

Climate Shocker: Warming Oceans Create Great Plumes of Methane Bubbles Near Atlantic Coast

The bubbles could add some 90 tons of greenhouse gases to the atmosphere.

Photo Credit: Gumenyuk Dmitriy/Shutterstock

Streams of methane bubbles are percolating along the Atlantic coast between North Carolina’s Outer Banks and Massachusetts’ Cape Cod.

According to the journal Nature, surges of bubbles are flowing from hundreds of ocean-floor leaks. Researchers say the plumes likely contain methane and could add as much as 90 tons of methane—a greenhouse gas much more potent than carbon dioxide — to the atmosphere each year. The methane bubbles may also hasten ocean acidification.

In the Geoscience newsletter published by Nature, researchers say that some two-thirds of the methane emissions come from methane-rich ices deep in the ocean that may be decomposing due to warming waters along the ocean floor. What influence these emissions will have on the atmosphere or the chemical makeup of the ocean is not immediately clear, but scientists are concerned. 

The bubbles first came into view on sonar scans of the ocean floor during oceanographic expeditions between 2011 and 2013. The expeditions ranged from Cape Hatteras in North Carolina to Georges Bank off Cape Cod and covered more than 36,000 square miles, an area about the size of Indiana. The scanned area includes the margin of the continental shelf and the sloping areas seaward and to the east.

Within a distance of about 590 miles, researchers found some 570 bubble plumes, which is considered to be an extraordinary amount. Previously, researchers studying the area had only detected an incidental number of bubble plumes. While some of the plumes extended far from the ocean floor, most of the bubbles dissolved into the water before they could reach the water’s surface.

The next step for the oceanographic researchers is to collect samples of the bubbles, says Carolyn Ruppel, a geophysicist at the U.S. Geological Survey at the Woods Hole, Massachusetts field center and a co-author of the study.

Ruppel found that the plumes contain methane by examining their sources. She says some of the plumes are coming from shallow ocean areas that were once methane-producing wetlands during the last Ice Age. During that period, sea levels were much lower than they are today.

Still, Ruppel notes that many of the seeps producing methane lie along the continental slope at cold depths. Ices there have formed in sea floor sediments under high pressure. These ices, which appear to be melting, hold methane produced by microbes that once lived on the ocean floor. It is surmised that warming ocean waters are now causing the ices to melt. Methane leaks aren’t typically found along continental shelves. The largest sources of methane in the oceans are known reservoirs near active tectonic regions.

Methane can react with oxygen in the water to create carbon dioxide, which in turn, can add to the acidification of ocean waters. Such acidification occurs when pH levels fall in the ocean. The lower the pH, the higher the acid. So falling pH levels in the ocean means that acid is increasing, which has major impacts for species that live in the sea, particularly animals that build calcium-based shells.

The observed increase of carbon-dioxide concentrations in our oceans is considered unparalleled in the Earth's history over the past 20 million years. Scientists are uncertain of the extent marine fauna can adapt to it over extended time periods.

“Studies have shown that a more acidic environment has a dramatic effect on some calcifying species, including oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton,” the National Oceanic and Atmospheric Administration states. "When shelled organisms are at risk, the entire food web may also be at risk. Today, more than a billion people worldwide rely on food from the ocean as their primary source of protein. Many jobs and economies in the U.S. and around the world depend on the fish and shellfish in our oceans.”

While 90 tons may seem like an alarming figure, it’s still much smaller than the amount created by industry, agriculture and other known sources. However, researchers caution that there are far more than 570 of these plumes in our oceans, estimating that there could be 30,000 or more active methane plumes.

Cliff Weathers is the communications director at Riverkeeper, New York's clean water advocacy organization. He is a former senior editor at AlterNet and served as a deputy editor at Consumer Reports. Twitter @cliffweathers.