In what could be a clue to the future effects of climate change, scientists have discovered a huge collection of methane leaks from the ocean floor off the United States’ eastern seaboard.
Their work, published Sunday in Nature Geoscience, used a research vessel equipped with sonar to map a 94,000-square-kilometer area that arcs from North Carolina up to Massachusetts. Within that expanse, according to Scientific American, they discovered around 570 separate plumes of bubbles rising from the floor of the Atlantic Ocean. And while the scientists haven’t yet collected samples, the bubbles’ sources suggest they contain methane.
The study is surprising, because such leaks are usually found atop known methane reservoirs — or above active tectonic regions — and scientists had previously thought very few such leaks were to be found in that area of the Atlantic shelf. “This is the first time anyone has systematically mapped an entire margin,” Christian Berndt, a marine geophysicist at GEOMAR in Kiel, Germany, who was not involved in the study, told Science Magazine. “They found that there was much more methane coming out than was suspected beforehand.”
Methane is a greenhouse gas, far more potent on a pound-for-pound basis than carbon dioxide. But at 90 metric tons per ear, the methane being released by the 570 leaks is dwarfed by the annual releases from human industrial and agricultural activity, as well as other natural sources. Still, the researchers estimate there could around 30,000 more of the leaks all over the world.
There’s also the possibility that climate change and alterations to ocean temperatures could lead to far bigger releases.
“These little bits of bubbling here or there will not make a memorable impact,” Jens Greinert, who heads the deep-sea monitoring unit at GEOMAR, told Science Magazine. “It becomes interesting only if you have a catastrophic release.”
Carolyn Ruppel of the United States Geological Survey, one of the study’s co-authors, told the New York Times that about 40 of the leaks they detected came from depths of over 3,300 feet, likely originating from deeper reservoirs below the initial sediments that make up the sea floor. If that’s the case, those reservoirs could be a target for extraction by fossil fuel companies, though more research will be needed to confirm. But most of the leaks came from 800 to 2,000 feet down, and pictures Ruppel and her colleagues were able to take with a submersible show that most of the methane is likely trapped in ice structures called hydrates in the initial sediments at the seabed.
That raises the possibility that the hydrates, which are extremely sensitive to changes in temperature, are being melted by warming waters. That heat could be brought by natural cycles and variability — or by climate change. Another twist is that most of the methane is absorbed by the ocean long before it breaches the surface. The process reacts with oxygen and releases carbon dioxide, which in turn increases the acidification of the ocean in the vicinity. So there’s the possibility that warming waters from climate change could release more methane, thus further speeding up the ocean acidification that is itself being driven largely by humanity’s carbon dioxide emissions.
But with the current evidence, what connection can be drawn to climate change — if any at all — remains unclear. The undersea pictures taken by the research team suggest at least some of the methane leaks have been active for hundreds of years or even a millennia.
“It highlights a really key area where we can test some of the more radical hypotheses about climate change,” John Kessler, a professor at the University of Rochester who was not involved in the research, told the New York Times. “How will those release rates accelerate as bottom temperature warms, or how will they decelerate if there are some cooling events?”
“We don’t really have all of the answers. But this is a great place to try to find them.”