In 2018, Chinese geologists created a methane leak in the South China Sea.
They were trying to figure out how much natural gas might exist in marine sediments, so they drilled a hole in the seafloor, as part of their work for the government-owned China Geological Survey.
Afterward, they tried to seal the hole with heavy mud. It measured just 22 centimeters (9 inches) wide. But their attempt failed.
A year later, a plume of methane gas had shot up from the deep, rising more than a kilometer high into the water column.
It was a mistake that scientists thought would take decades, if not a century, to naturally resolve.
Then, something incredible happened.
Using echosounders, underwater cameras, and chemical sensors, researchers watched in awe as a swarm of ocean life flocked to the hole and contained the leaking gas with “remarkable speed“.
“Within just one to two years, an effective methane-consuming ecosystem had already formed,” says microbial ecologist Emil Ruff of the University of Bremen in Germany.
According to past models, a fully functioning methane-munching community on the ocean floor can take between 60 and 100 years to develop.
This one was chewing through nearly as much methane in a fraction of the time.
The first lifeforms to arrive on the scene were methane-munching bacteria and archaea. Overall, the diversity of microbes in the sediments took a hit, but species that consume methane thrived.
These single-celled organisms were then followed by an influx of burrowing invertebrates, which created an extensive ‘worm bed’ over the hole.
Crustaceans crawled to the scene as well.
“The worms, in turn, benefited from the newly established microorganisms, which likely served as a food source,” explains Ruff.
“Animals and microorganisms thus contributed jointly to methane breakdown.”
As tube worms burrowed into the seafloor, they helped mix the sediment, and this probably transported oxygen, nitrate, and sulfate into deeper layers, says Ruff.
Before the hole was drilled, there was no detection of gas flow and only scarce seafloor colonization in this particular spot.
With just one poke, however, everything changed. Scientists accidentally let trapped methane loose, restructuring the local ecosystem as a result.
Bubbles of methane were still leaking from the hole in 2023, but as the living filter developed, the plume’s height fell from 1,200 meters (0.74 miles) above the seafloor to roughly 800 meters.
That might sound like a promising turn of events, but this research points to a larger problem.
Seafloor sediments are home to Earth’s largest reservoir of methane, and natural cracks in the ocean floor allow some of that gas to seep out. This can support thriving ecosystems in the deep, dark ocean where sunlight and nutrients are scarce.
But methane is also a major greenhouse gas, accounting for about 11 percent of global emissions and trapping vastly more heat than carbon dioxide.
Today, we know that abandoned oil and gas wells on the ocean floor can be a large source of methane (not to mention the massive leaks seen rising from terrestrial infrastructure and subsea pipelines).
In 2012 and 2013, for instance, scientists in Germany observed methane bubbles leaking from seabed areas around abandoned wells in the North Sea.
Later, a follow-up study found leaks at 28 out of 43 wells examined (63 percent).
“The results clearly show that thousands of tons of methane are leaking from old drill holes on the North Sea floor every year,” marine geoscientist Christoph Böttner, the study’s main author, said in 2020.
What isn’t clear just yet is how much of that methane makes it out of the ocean and into the atmosphere.
In 2025, simluations found that methane leaks in the ocean that were deeper than 300 meters (985 feet) may not contribute much to atmospheric greenhouse gases, after all.
Most of the methane from these deeper sources dissolves in the water column, according to models.
But even if methane stays in the ocean, a surge can still lead to local troubles, including oxygen depletion, acidification, and a major restructuring of the ecosystem.
That doesn’t bode well for the South China Sea, where scientists are investigating a future commercial methane-hydrate industry.
From 2010 to 2020, Chinese programs completed more than 80 drilling evaluation wells in the South China Sea.
It’s unknown how many of these were successfully sealed or how they impacted the local environment.
This new study is one of the first to track a leak over several years.
It found that the wider seabed ecosystem was impacted within just a few years of human disturbance.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>“Extensive sampling at more than 40 sites surrounding the discharge center revealed the occurrence of elevated methane concentrations in surface sediments even at a 500-meter distance from the discharge center,” the study authors write.
“This was accompanied by a more than 30 percent reduction in microbial richness.”
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More research is needed, but the study authors suspect that even micromolar increases in sediment methane are linked to significantly lower microbial diversity and lower oxygen.
If methane’s impact as a greenhouse gas in the atmosphere is becoming increasingly clear through super-charged weather events, its impact on deep-sea ecosystems is only just coming to light.
The study is published in the peer-reviewed journal National Science Review.
This article was fact-checked by Clare Watson and edited by Clare Watson. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
