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Robert McSweeney

Robert McSweeney

26.08.2014 | 3:39pm
OceansWidespread methane leakage found on US Atlantic coast
OCEANS | August 26. 2014. 15:39
Widespread methane leakage found on US Atlantic coast

New research has found evidence of methane leaking from under the sea floor on the Atlantic Coast of the US. Could this be the beginnings of a huge release of methane into our atmosphere? Scientists tell us probably not.

Seabed seeps

The research has identified hundreds of ‘seeps’ along the American Atlantic coast – places where gas bubbles out of the sea floor. This could be just the beginning, with perhaps “tens of thousands” more seeps to discover, the researchers say.

They also say it’s likely the bubbling gases include methane – a powerful but short-lived greenhouse gas. Methane stored under the seabed is one of the largest reserves of methane on the planet – a companion article describes the overall size of the reservoir as “staggering”.

Nature Geoscience _Methane Seeps _Aug 14

Methane streaming from the seabed. Source: Skarke et al. (2014)

Scientists knew such seeps were present in the Arctic ocean. But large scale leakage in the mid-Atlantic has come as a surprise, with scientists previously aware of only three areas of seepage.

So is this a new source of greenhouse gases to worry about, and will these seeps have a profound impact on the global climate? The authors of the new research think not.

No evidence

Last year a debate erupted amongst scientists following a comment piece in Nature suggesting climate change could cause huge quantities of methane to be released from the Arctic seabed.

But in this case, the paper’s authors observe that seafloor emissions have continued for “more than 1,000 years” at some seeps. There is no suggestion of any increase in emissions.

Professor David Archer of the University of Chicago agrees. He tells us that “there is no evidence for an increase in emission, and lots of evidence that it’s been going on for a while.”

While it is likely that as global temperatures rise more methane will be emitted from such seafloor reservoirs, Archer doubts the amount released will be big when compared to other natural sources.

He says:

“[T]he methane concentration in the atmosphere is dominated by tropical wetlands and human emissions, so I expect the actual climate forcing from methane released from the ocean, or the Arctic, to be small.”

Other impacts

So what’s the importance of the research? First, it raises the question of where else widespread methane leakage might occur. If seafloor emissions are large, this could radically change calculations of natural carbon emissions, as the BBC reports.

Secondly, if the seeps are releasing methane, this could have implications for marine life. Methane causes an increase in acidity and reduction in the oxygen content of seawater. Even small shifts in acidity can make it more difficult for small marine creatures to form shells. These creatures are the foundation of ocean food webs, and so any impact on them will have knock-on effects.

So while the research doesn’t suggest a huge increase in methane emissions to the atmosphere, the wider impacts of these findings may have significant implications for the world’s oceans nonetheless.

A. Skarke et al. (2014) Widespread methane leakage from the sea floor on the northern US Atlantic margin, Nature Geoscience, doi.org/10.1038/ngeo2233


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