Scientists have uncovered a previously misunderstood source of methane lurking in the world’s oceans, that could grow more potent as global temperatures rise, potentially triggering a dangerous feedback loop that accelerates climate change.

A new study published in the Proceedings of the National Academy of Sciences by researchers at the University of Rochester has identified a key mechanism driving methane production in the open ocean.

For years, oceanographers have been stumped by a contradiction in their findings. Surface ocean waters, which are rich in oxygen, consistently release methane into the atmosphere.  

Methane is typically generated in oxygen-free environments, like wetlands or deep-sea sediments. Its production at the surface was therefore a mystery.

This new study seems to have resolved this contradiction. 

Certain bacteria produce methane as they break down organic material, but only when phosphate, an essential nutrient, is scarce. Using a global dataset and computer modelling, the team found methane is being generated in nutrient-poor regions of the ocean.

“This means that phosphate scarcity is the primary control knob for methane production and emissions in the open ocean,” said Thomas Weber, associate professor in the Department of Earth and Environmental Sciences at Rochester, who led the research.

As climate change warms the ocean from the surface downward, the density difference between surface and deeper water increases, slowing the vertical mixing that carries nutrients like phosphate up from depth.

Surface waters are therefore likely to become increasingly phosphate-depleted over time, allowing methane production to flourish in these parts of the ocean.

The result is a worrying cycle: warmer oceans reduce nutrient mixing, methane-producing bacteria increase, more methane enters the atmosphere, and warming intensifies further. 

Importantly, this type of feedback is not yet accounted for in most major climate models.

Weber warned that closing this gap in our understanding is urgent. 

“Our work will help fill a key gap in climate predictions, which often overlook interactions between the changing environment and natural greenhouse gas sources to the atmosphere,” he said.

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