A previously unrecognised biological sink for methane, a gas that contributes to climate change, has been reported this week in Nature Communications. The research shows that abundant microorganisms living in carbonate rocks in the deep sea use methane for respiration, removing methane from the ocean on a global scale. Methane is a significant contributor to greenhouse forcing, and determining its fluxes and reservoirs is important for understanding the methane cycle.

Victoria Orphan and colleagues investigate carbonate rocks associated with three different cold seeps (areas of the ocean floor where methane and other hydrocarbon-rich fluid seepage occurs naturally). Carbonate rocks in these areas were previously thought to be passive recorders of methane oxidation over time; however, the authors find that microorganisms living within the rocks are actively utilising methane and consuming it. This is a previously-unrecognised ecological niche for these important methane consumers.

The microorganisms were found to be capable of methane oxidation in both oxygenated and low oxygen conditions. The carbonate rocks hosting these microbial communities are difficult to sample, being at water depths of more than 500m, but it is likely that similar communities exist in many other parts of the ocean and may be a significant sink for methane globally.