Microbes in the ocean are helping to keep our planet's temperature stable by preventing greenhouse gas methane from bubbling out of the sea, research has shown.
Scientists still don't fully understand how the microbes consume methane so quickly.
Methane's warming effect is up to 30 times as powerful as carbon dioxide.
In recent years, researchers have found more and more methane beneath the seafloor, yet very little ever leaves the oceans and gets into the atmosphere.
Now researchers know why.
Harvard University scientists found that the methane is being consumed rapidly by communities of microbes, preventing it from escaping.
Peter Girguis, professor of organismic and evolutionary biology at Harvard, said: "The microbes in these carbonate rocks are acting like a methane bio filter consuming it all before it leaves the ocean."
Seafloor carbonate rocks are common, and in some places they form unusual chimney-like structures.
These chimneys reach 12 to 60 inches in height and are found in groups along the seafloor resembling a stand of trees.
Unlike many other types of rocks, these carbonate rocks are porous, creating channels that are home to a very dense community of methane-consuming microbes.
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During a 2015 expedition funded by the Ocean Exploration Trust, Girguis discovered a carbonate chimney reef off the coast of southern California at the deep sea site Point Dume.
Girguis returned in 2017 with funding from Nasa to build a seafloor observatory.
He said: "We measured the rate at which the microbes from the carbonates eat methane compared to microbes in sediment.
"We discovered the microbes living in the carbonates consume methane 50 times faster than microbes in the sediment. We often see that some sediment microbes from methane-rich mud volcanoes, for example, may be five to 10 times faster at eating methane, but 50 times faster is a whole new thing.
"Moreover, these rates are among the highest, if not the highest, we've measured anywhere.
"These rates of methane oxidation, or consumption, are really extraordinary, and we set out to understand why."
The team found that the carbonate chimney set up an ideal home for the microbes to eat a lot of methane really fast.
Researcher Jeffrey J. Marlow said: "These chimneys exist because some methane in fluid flowing out from the subsurface is transformed by the microbes into bicarbonate, which can then precipitate out of the seawater as carbonate rock.
"We're still trying to figure out where that fluid – and its methane – is coming from."
One find was that, in some cases, these microbes were surrounded by pyrite, which is electrically conductive.
One possible explanation for the high rates of methane consumption is that the pyrite provides an electrical conduit that passes electrons back and forth, allowing the microbes to have higher metabolic rates and consume methane quickly.
Marlow said: "When microbes work together they're either exchanging building blocks like carbon or nitrogen, or they're exchanging energy. And one kind of way to do that is through electrons, like an energy currency. The pyrite interspersed throughout these carbonate rocks could help that electron exchange happen more swiftly and broadly."
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