A Strip of the Atlantic Ocean Floor Has Been Belching Methane For 1000 Years

In highly tectonic regions of the Earth’s crust, or in areas connected to deep petroleum basins, methane streams up from the ocean floor. In other places, these gaseous seeps are much less common. Now, though, scientists have discovered methane bubbling from at least 570 locations on the Atlantic Ocean floor where the continental shelf meets the deeper sea—generally, a tectonically calm place.

And some of these plumes are likely more than 1,000 years old.

Methane bubbling up from the ocean floor near the coast of Virginia.

At approximately 40 of the seeps, the methane could be originating in deeper reservoirs of the gas and traveling upward through layers of sediment.

Here’s Henry Fountain, writing for The New York Times:

But Dr. Ruppel said most of the seeps had been found in depths of about 800 to 2,000 feet, where the methane, which is produced by microbes, is most likely trapped in sediments near the seafloor, within cagelike molecules of ice called hydrates. Natural variability in water temperatures, caused by ocean circulation and other factors, may be warming these hydrates just enough to release the gas.

Hydrates at such relatively shallow depths “are exquisitely sensitive to small changes in temperature,” she said. “You don’t have to change things very much to get the methane to come out.”

In other words, the area (which extends from Cape Hatteras, N.C. to the Georges Bank southeast of Nantucket, M.A.) is a convenient spot for researchers to study the links between climate change, methane emission, and ocean acidification—particularly because it’s not a tectonically active place.

Here’s Sid Perkins, interviewing study co-author Adam Skarke for Nature:

Sampling the bubbles, along with the waters in and around the plumes, will help scientists to estimate the effects of the methane emissions, says Skarke. The gas reacts with, and thereby diminishes, dissolved oxygen, a process that creates carbon dioxide that will tend to acidify surrounding waters.

The scientists hope to use methane measurements from the area to determine how much of the gas is being produced, how it varies with ocean floor temperature, how the seeps have evolved over time, and if there are any other unexplored ocean plume communities. These are some big questions that could generously contribute to the study of our changing planet.