A new study published in the journal Proceedings of the National Academy of Sciences reveals an important driver of methane production in the open ocean. Researchers at the University of Rochester, including Thomas Weber, an associate professor in the Department of Earth and Environmental Sciences, along with graduate student Shengyu Wang and postdoctoral research associate Hairong Xu, identified a mechanism that could become more active as the planet warms. This raises concerns about a feedback loop that could intensify climate change.

Methane is a highly potent greenhouse gas. For years, scientists have been puzzled by a contradiction. Surface ocean waters, which contain plenty of oxygen, consistently release methane into the atmosphere. This is unexpected because methane is usually produced in environments that lack oxygen, such as wetlands or deep ocean sediments.

Microbes and Phosphate Drive Methane Production

To investigate this mystery, Weber's team analyzed a global dataset and used computer models. Their results point to a specific microbial process. Certain bacteria produce methane as they break down organic material, but this only happens when phosphate, an essential nutrient, is in short supply.

"This means that phosphate scarcity is the primary control knob for methane production and emissions in the open ocean," Weber says.

These findings reshape how scientists think about methane in the ocean. Instead of being rare, methane production in oxygen-rich waters may be common in regions where phosphate levels are low.

Warming Oceans May Increase Methane Emissions

The research also looks ahead to how this process could evolve in a warming world. Climate change is heating the ocean from the surface downward, which increases the difference in density between surface water and deeper layers.

"Climate change is warming the ocean from the top down, increasing the density difference between surface and deep waters," Weber says. "This is expected to slow the vertical mixing that carries nutrients like phosphate up from depth."

With less mixing, fewer nutrients reach the surface. According to the team's model, this could leave surface waters increasingly depleted of phosphate, creating ideal conditions for methane-producing microbes to grow.

A Potential Climate Feedback Loop

If this happens, the ocean could release more methane into the atmosphere. Because methane is such a powerful greenhouse gas, this sets up a concerning cycle. Warmer oceans lead to more methane emissions, which then contribute to further warming.

The study highlights how microscopic processes in the ocean can have far-reaching global impacts.

Missing Piece in Climate Models

Importantly, this type of feedback is not yet included in most major climate models. As scientists work to improve predictions, accounting for interactions like this could be critical for understanding how quickly and how severely climate change will progress.

"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," Weber says.