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Earthquakes ‘May Contribute to Methane Leaks’

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By Tim Radford, Climate News Network

LONDON – And here’s another shuddering twist to the horror story that is climate change: even earthquakes may play a role. Large quantities of methane may have escaped during a violent earthquake that shook the floor of the Arabian Sea in 1945, according to German and Swiss researchers.

David Fischer of the University of Bremen and colleagues from the Alfred Wegener Institute in Bremerhaven and the ETH in Zurich explored the region in a research ship in 2007, and began to examine cores of sediment from the seabed.

Sediment coring in Greenland: coring in the Arabian Sea gave researchers the clue they needed.
Credit: Hannes Grobe, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, via Wikimedia Commons

One core, from just 1.6 meters (5.25 feet) below the seabed, contained methane hydrate – an ice-like mixture of methane and water -  and the other did not. But, the researchers report in Nature Geoscience, both cores carried subtle chemical evidence that at some point in the past dramatic quantities of methane or natural gas had actually flowed through the sediments beneath the Arabian Sea.

Since the methane would move as a gas, there is only one direction it could go: bubbling upwards through the sea into the atmosphere. And since methane is a potent greenhouse gas – at least 23 times more potent than carbon dioxide – such escapes could be significant.

“We started going through the literature and found that a major earthquake had occurred close by in 1945”, said Dr. Fischer. “Based on several indicators, we postulated that the earthquake led to the fracturing of the sediments, releasing the gas that had been trapped below the hydrates into the ocean.”

The tremor was recorded at magnitude 8.1 – magnitude 9 is about as bad as an earthquake can be – and seismic waves would have raced through the seabed at colossal speeds, quite enough to shake loose any brittle chemical structures in the seabed.

The researchers estimate that the release of methane from that location since that one event could be conservatively estimated at 7.4 million cubic meters: this is roughly the capacity of 10 large gas tankers.

This calculation does not take into account how much escaped during the quake itself, and it holds for only one location. “There are probably even more sites in the area that had been affected by the earthquake,” said Dr. Fischer.

Methane gas bubbling out the top of an undersea mud volcano in the Gulf of Mexico.
Credit: NOAA

Such research is another reminder of the complexity of the planet’s climate system. Methane hydrates can be considered as a form of fossil fuel: decayed plant material from millions of years ago, trapped in the mud under the pressing weight of the sea.

Climate scientists have for decades worried about the fragility of these hydrates – as the world warms, they are likely to be released in huge quantities from the Arctic seabed, for instance – but this is the first evidence that natural rather than human-triggered cataclysms could make a serious difference to the global carbon budget.

The lesson is that scientists now have to take such processes into account as they try to calculate the carbon budget for the planet – the quantities of greenhouse gases released into the atmosphere, the volumes subsequently absorbed by plants and then incorporated into sediments.

“We now provide a new mechanism of carbon export that had not been considered before”, said Dr. Fischer, and with his co-authors he pushes the message home in the research paper. “We therefore suggest that hydrocarbon seepage triggered by earthquakes needs to be considered in local and global carbon budgets at active continental margins.”

Tim Radford is a reporter for Climate News Network. Climate News Network is a news service led by four veteran British environmental reporters and broadcasters. It delivers news and commentary about climate change for free to media outlets worldwide.

Comments

By WrenchMonkey
on August 3rd, 2013

So, let’s continue burning fossil fuels, forge ahead with fracking, which will induce earthquakes and contribute even more to global warming, build a mess of pipelines, guaranteed to leak, through fragile ecosystems and, while we’re at it, build a lot more nuclear power plants on fault systems and low-lying, coastal areas.

What could possibly go wrong?

Some few individuals will get really, really “rich” this way and, if they don’t get caught in any of the consequential “natural” catastrophes, will enjoy long lives of fabulous opulence and comfort. They really don’t give a rat’s ass what happens once they’ve had their fun.

The human experiment is an abject failure. Let’s hasten the extinction of homo sapiens before it ensures the eradication of all Life on Earth.

Seriously, in my opinion the human species has proved itself a failed evolutionary experiment that now threatens to turn Earth into a barren rock in its blind lust to consume. We behave more like a cancer than a “sentient” species.

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By Eric Peterson (Front Royal, VA 22630)
on August 3rd, 2013

“as the world warms, they are likely to be released in huge quantities from the Arctic seabed, for instance “

But earlier in the article we read that:

“One core, from just 1.6 meters (5.25 feet) below the seabed, contained methane hydrate – an ice-like mixture of methane and water ... beneath the Arabian Sea.

The Arabian Sea is at least 75F, yet still had frozen methane at the bottom.  I don’t think the Arctic will warm to 75F, maybe 35F at the most.

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By Bryan Bates (Burlington)
on August 5th, 2013

Come on people if you find it I will destroy it. I am the inventor of the Electric Filter. It is use by me to stop the world from pollution and little things like methane from getting into the atmosphere.

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By Dave (Basking Ridge, NJ 07920)
on August 5th, 2013

Eric: Stability of methane hydrates is a function of temperature and pressure. They remain stable to higher temperatures at higher pressures and vice versa.  So the temperature stability for methane hydrates in say Arctic permafrost or relatively shallow waters may be quite different from that for deposits contained in deep sea sediments. Unfortunately the article doesn’t identify the depth for this find. For instance, the stability line at a pressure corresponding to a water depth of 1000m (~3000ft) is about 10C (50F). Also, you assumed these Arabia Sea deposits would be in an environment of 75F, presumably because it is the Arabian Sea. Although surface/near surface temperatures would be warm at those latitudes, the respective environment is instead the bottom of the sea – “1.6m below the seabed” not below the sea surface. Temperatures of deep ocean waters tend to be generally quite cold.

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By William Hughes-Games (Waipara New Zealand)
on August 7th, 2013

There is another little twist to this story.  On the continental shelves a slopes, methane clathrate deposits occur below the sea floor.  Despite warming oceans, heat transfers very slowly through sediment to reach and destabilize such deposits. However, if earthquakes trigger land slides, such deposits can be exposed.  Sort of a mini St Helena where the land slide released the pressure on gas saturated magma.  On many of these slopes, all that is holding the sediment together is the “permafrost” made of methane clathrate.  As this starts to break down, the glue is removed and tremors can more easily trigger slumps.  Such land slides are known to produce localized by quite severe tsunamis.

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By Eric Peterson (Front Royal, VA 22630)
on August 8th, 2013

“Temperatures of deep ocean waters tend to be generally quite cold.”

Dave, the average temperature of all oceans, including the surface waters is less than 40F, so basically almost all of the oceans are cold   Anywhere below the thermocline will be cold and mostly cold enough to keep the methane hydrate intact.  Specifically in the Arctic “throughout most of the ocean, the stability depth is of order 500–700 m, shoaling to perhaps 200 m in the Arctic. Surface warming is expected to take order a century to reach these depths.”  See http://hal.archives-ouvertes.fr/docs/00/29/78/82/PDF/bgd-4-993-2007.pdf for lots of details.

The bottom line is we are talking about an extremely minor source in this article (earthquakes and landslides) and a major source only in the long run (beyond a few centuries).  The present day value of stopping those emissions is basically zero.

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