Ocean Life Sealed an Accidental Methane Leak in Years, Not the Century Scientists Expected

In 2018, Chinese geologists drilled a 22-centimetre-wide hole into the seafloor of the South China Sea while surveying marine sediments for natural gas, as part of work for the government-owned China Geological Survey. Their attempt to seal the hole with heavy mud failed, and by the following year a plume of methane gas was rising more than a kilometre through the water column, a leak scientists expected would take decades, if not a century, to resolve naturally.

Instead, researchers using echosounders, underwater cameras and chemical sensors watched a swarm of ocean life colonise the hole and contain the leaking gas with remarkable speed. 'Within just one to two years, an effective methane-consuming ecosystem had already formed,' said microbial ecologist Emil Ruff of the University of Bremen in Germany, whose past models suggest such a community usually takes 60 to 100 years to develop. The first arrivals were methane-munching bacteria and archaea; while overall microbial diversity in the sediment fell, species that consume methane thrived. Burrowing invertebrates followed, forming an extensive 'worm bed' over the hole, with crustaceans arriving as well.

'The worms, in turn, benefited from the newly established microorganisms, which likely served as a food source,' Ruff said. As tube worms burrowed into the seafloor, they helped mix the sediment, probably transporting oxygen, nitrate and sulfate into deeper layers. Before the accidental leak, this spot had shown no detectable gas flow and only scarce seafloor life. Bubbles were still escaping the hole in 2023, but as the living filter developed, the plume's height fell from 1,200 metres above the seafloor to roughly 800 metres.

The wider ecosystem was still affected: extensive sampling at more than 40 sites around the leak found elevated methane in surface sediments even 500 metres away, accompanied by more than a 30% reduction in microbial richness. Methane is a major greenhouse gas, accounting for about 11% of global emissions and trapping far more heat than carbon dioxide, and seafloor sediments hold Earth's largest reservoir of it. Abandoned oil and gas wells can be a significant source: a follow-up study in the North Sea found leaks at 28 of 43 abandoned wells examined, and marine geoscientist Christoph Bottner said in 2020 that thousands of tons of methane leak from old North Sea drill holes every year.

From 2010 to 2020, Chinese programs completed more than 80 drilling evaluation wells in the South China Sea, where a future commercial methane-hydrate industry is being investigated, and it is not known how many of these wells were successfully sealed or how they affected the local environment. The study, one of the first to track such a leak over several years, was published in the journal National Science Review.