Scientists discover carbonate rocks are unrecognized methane sink

Since the first undersea methane seep was discovered 30 years ago, scientists have meticulously analyzed and measured how microbes in the seafloor sediments consume the greenhouse gas methane as part of understanding how the Earth works.

The sediment-based microbes form an important methane "sink," preventing much of the chemical from reaching the atmosphere and contributing to greenhouse gas accumulation. As a byproduct of this process, the microbes create a type of rock known as authigenic carbonate, which while interesting to scientists was not thought to be involved in the processing of methane.

That is no longer the case. A team of scientists has discovered that these authigenic carbonate rocks also contain vast amounts of active microbes that take up methane. The results of their study, which was funded by the National Science Foundation, were reported today in the journal Nature Communications.

"No one had really examined these rocks as living habitats before," noted Andrew Thurber, an Oregon State University marine ecologist and co-author on the paper. "It was just assumed that they were inactive. In previous studies, we had seen remnants of microbes in the rocks – DNA and lipids – but we thought they were relics of past activity. We didn't know they were active.

"This goes to show how the global methane process is still rather poorly understood," Thurber added.

Lead author Jeffrey Marlow of the California Institute of Technology and his colleagues studied samples from authigenic compounds off the coasts of the Pacific Northwest (Hydrate Ridge), northern California (Eel River Basin) and central America (the Costa Rica margin). The rocks range in size and distribution from small pebbles to carbonate "pavement" stretching dozens of square miles.

"Methane-derived carbonates represent a large volume within many seep systems and finding active methane-consuming archaea and bacteria in the interior of these carbonate rocks extends the known habitat for methane-consuming microorganisms beyond the relatively thin layer of sediment that may overlay a carbonate mound," said Marlow, a geobiology graduate student in the lab of Victoria Orphan of Caltech.

These assemblages are also found in the Gulf of Mexico as well as off Chile, New Zealand, Africa, Europe – "and pretty much every ocean basin in the world," noted Thurber, an assistant professor (senior research) in Oregon State's College of Earth, Ocean, and Atmospheric Sciences.

The study is important, scientists say, because the rock-based microbes potentially may consume a huge amount of methane. The microbes were less active than those found in the sediment, but were more abundant – and the areas they inhabit are extensive, making their importance potential enormous. Studies have found that approximately 3-6 percent of the methane in the atmosphere is from marine sources – and this number is so low due to microbes in the ocean sediments consuming some 60-90 percent of the methane that would otherwise escape.

Now those ratios will have to be re-examined to determine how much of the methane sink can be attributed to in rocks versus those in sediments. The distinction is important, the researchers say, because it is an unrecognized sink for a potentially very important .

"We found that these located in areas of active methane seeps are themselves more active," Thurber said. "Rocks located in comparatively inactive regions had little microbial activity. However, they can quickly activate when methane becomes available.

"In some ways, these rocks are like armies waiting in the wings to be called upon when needed to absorb methane."

The ocean contains vast amounts of methane, which has long been a concern to scientists. Marine reservoirs of methane are estimated to total more than 455 gigatons and may be as much as 10,000 gigatons carbon in . A gigaton is approximate 1.1 billion tons.

By contrast, all of the planet's gas and oil deposits are thought to total about 200-300 gigatons of carbon.

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Journal information: Nature Communications

Citation: Scientists discover carbonate rocks are unrecognized methane sink (2014, October 15) retrieved 17 July 2019 from
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Oct 15, 2014
This goes to show how the global methane process is still rather poorly understood,

Sweet. Good thing our politicians aren't basing trillion-dollar policy decisions on it, then! Oh... dang...

Oct 15, 2014
Hmmm whats the breakdown product of the bacteria digesting the Methane? Taking into account that the bacteria live in the body of the rock one would assume the breakdown product is not carbonate.

Also what would be the geochemical signature of the breakdown product if the source was thermogenic gas?

I would be interested to see how this is modelled in current climate models. Anyone have a good link for that?

Oct 15, 2014
Progressive democrats Global warmist told me that Methane is bad and will destroy the world right alongside carbon dioxide.

Oh well..... surely a vote for a democrats isn't a vote for corruption is it?

Sorry for posting the above link..... it just another example of "if you vote democrat, you vote for corruption."

Oct 16, 2014
Stupid trolls are stupid - these methane mechanisms are not the worst contributors to uncertainty about AGW, and the observations are now certain enough on their own (3 sigma) - but rock life is always interesting in itself. It was one of the first biotopes in many emergence of life theories.

@weathervane: I think the point here is that it was an unknown sink. Methanotrophs oxidize methane to formaldehyde, which they use internally. [ http://en.wikiped...anotroph ] As always, IPCC is the go-to resource on the current status of climate science, it's its purpose..

Oct 18, 2014
Oh thanks for the link. From the link page seems like there are two routes for metabolism one aerobic and the other anaerobic. The pathway you are suggesting appears to be he aerobic one but not sure where the microbes buried in the rock get their O2 from? Also wonder what happens to the pore space as colonies grow ....unless they are also dissolving the host rock...which I guess some other species are known to do?

My guess is that these bugs would be working anaerobicly, but from the wiki page that pathway is poorly understould but looks like it uses the process in reverse to produce co2 and other products, interesting.

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