There has never been anything particularly dramatic about the seafloor off the US East Coast. For a long time, the Atlantic margin was classified as passive—geologically stable and reasonably predictable—in contrast to the tectonically restless Pacific or the oil-rich Gulf of Mexico. In a way that few researchers expected, that assumption is now appearing dubious.
Methane is seeping from the Atlantic Ocean floor at rates and locations that don’t neatly fit into current models, according to research conducted by Duke University scientists and their partners. At depths ranging from roughly 50 meters to 1,700 meters, more than 500 bubbling vents were found along the continental margin between North Carolina and Massachusetts. Just the number was startling. Only three such seep areas beyond the edge of the continental shelf had been discovered in earlier surveys of the same coastline. The map is nearly completely rewritten when 570 is found.
The majority of these seeps cluster together, which makes them especially noteworthy. Most of them are located at a depth of about 500 meters, where the temperature and pressure are nearly perfect for the formation of methane hydrate, a sludgy, frozen substance that traps gas inside an ice lattice. As ocean temperatures rise, those hydrates may destabilize, releasing methane into the water column in ever-larger pulses. This is a scientifically plausible but unconfirmed concern.
The amount of that methane that is entering the atmosphere is still unknown. According to the majority of the data gathered, the gas seems to dissolve into the ocean at depth, where it oxidizes into carbon dioxide instead of escaping into the atmosphere above. Methane and CO2 have very different warming potentials over short time horizons, so that distinction is important. However, it would be incorrect to view that discovery as completely comforting. Scientists are still figuring out how chemistry, acidification, and ecosystems are impacted by carbon entering the ocean in any form.
The scale that is implied here is almost disorienting. According to researchers working on this project, if you extrapolate these results globally, there might be up to 30,000 seep systems that haven’t been mapped or counted before. It is estimated that the carbon content of the submerged sediments containing methane hydrate is approximately ten times greater than that of the atmosphere as a whole. Numerous research organizations, including the US Geological Survey, have cited that estimate, so it is not a fringe estimate. It’s worth taking a moment to sit with that number.
These seeps’ biological component is also subtly amazing. Scientists discovered chemosynthetic communities—organisms that get their energy from chemical reactions connected to the gas itself rather than from sunlight—around many of the venting sites. Based on isotope dating of carbonate rocks formed at the seafloor, it appears that methane has supported these ecosystems, which are mainly invisible to the surface world, for at least 15,000 years. In other words, the Atlantic margin was biologically alive in a way that no one had recorded, in addition to being geologically active.
The seeps themselves have not changed. They have existed for thousands of years. What has changed is that a long-stable system may be being pushed toward something less stable by warming ocean water. It’s truly unclear if that change will be gradual, dramatic, or somewhere in between. The researchers themselves have taken care to avoid making exaggerated claims. According to the data, the seeps are real and have been there for a very long time. It does not yet demonstrate whether they are accelerating, at least not conclusively.
Perhaps the most honest aspect of this story is that uncertainty. Seldom does science reach a definitive conclusion, particularly when the system under study is as vast and unreachable as the ocean floor. However, discovering 570 methane seeps when science had only previously recorded three is the kind of outcome that usually sticks with you. It implies that something important may be missing from the baseline assumptions incorporated into global carbon models, something that has been simmering beneath the surface all along.
