The world’s oceans may be playing a bigger role in climate change than scientists once realized, quietly accelerating global warming through processes that are only now coming into focus.
New research published in journal Proceedings of the National Academy of Sciences We reveal important factors for methane production in the open ocean. Researchers at the University of Rochester, including Thomas Webber, associate professor in the Department of Earth and Environmental Sciences, along with graduate student Shengyu Wang and postdoctoral researcher Hairong Xu, have identified a mechanism that may become more active as the planet warms. This raises concerns about feedback loops that could intensify climate change.
Methane is a very powerful greenhouse gas. For years, scientists have been plagued by a contradiction. Oxygen-rich surface ocean water continually releases methane into the atmosphere. This is unexpected because methane is typically produced in oxygen-deficient environments such as wetlands and deep-sea sediments.
Microbes and phosphates promote methane production
To investigate this mystery, Weber’s team analyzed global datasets and used computer models. Their results point to specific microbial processes. Certain bacteria produce methane when they break down organic matter, but this only occurs when the essential nutrient phosphate is lacking.
“This means that phosphate scarcity is the main control on methane production and emissions in the open ocean,” Weber says.
These discoveries reshape how scientists think about ocean methane. Methane production in oxygen-rich waters is not uncommon and may be common in areas with low phosphate levels.
Ocean warming could increase methane emissions
The study also looks at how this process might evolve in a warming world. Climate change is heating the ocean from the surface down, increasing the difference in density between surface and deep water.
“Climate change is warming the oceans from top to bottom, increasing the density difference between surface and deep water,” Weber said. “This is expected to slow down the vertical mixing that transports nutrients such as phosphate from deeper layers.”
Less mixing means less nutrients reaching the surface. According to the researchers’ models, this could lead to increasingly less phosphate in surface waters, creating ideal conditions for methane-producing microorganisms to thrive.
Potential climate feedback loops
If this happens, the ocean could release even more methane into the atmosphere. This creates an alarming cycle because methane is a very powerful greenhouse gas. As ocean temperatures rise, methane emissions increase, leading to further global warming.
This study highlights that microscopic processes in the ocean can have far-reaching impacts on a global scale.
Missing parts of climate models
Importantly, this type of feedback is not yet incorporated into most major climate models. Accounting for such interactions could be important for understanding how fast and how severely climate change progresses as scientists work to improve predictions.
“Our research helps fill an important gap in climate projections that often overlook interactions between the changing environment and natural greenhouse gas sources to the atmosphere,” Weber said.
