Ocean Currents Hinder Methane-Eating Bacteria

Methane comes from a variety of sources, both natural and man-made. This includes methane-munching microbes that live in rocks in the deep sea, helping to control this potent greenhouse gas. But now new research shows that ocean currents may be hindering these critical methane-eating bacteria, thus contributing to global warming.

Offshore the Svalbard archipelago, researchers found that methane gas is seeping out of the seabed at the depths of several hundred meters. Normally, communities of microorganisms that survive on methane gas control its concentration in the ocean, and stop it from reaching the ocean surface and released into the atmosphere.

In fact, they eat about 80 to 90 percent of the world's methane released through previously studied seeps, or cracks in the ocean floor.

However, a new study published in Nature Geoscience shows that ocean currents can have a strong impact on this bacterial methane filter.

After studying methane-consuming bacteria off the archipelago in the Arctic Ocean, the international research team noticed that activity varied drastically over very short time spans. They blame the West Spitsbergen Current, which carries warm water from Norwegian Sea to Arctic Ocean. It turns out over the study period, oceanographic factors such as water temperature and salinity changed, causing fluctuations in bacterial communities.

Specifically, the warm and salty current swept over the methane seeping sites, and carried bacteria communities away, thus disturbing methane filtration processes.

"We were able to show that strength and variability of ocean currents control the prevalence of methanotrophic bacteria," lead study author Lea Steinle said in a statement, "therefore, large bacteria populations cannot develop in a strong current, which consequently leads to less methane consumption."

This bacteria filter could become even more important in the future, because environmental changes can cause bottom water warming in the Arctic Ocean.

As a consequence, methane rich gas hydrates in the ocean floor could dissociate, and release even more gas into the water column, thereby letting it escape into the atmosphere.

Future methane release from the ocean to the atmosphere and thus global warming will depend on ocean currents.

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