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How the Gulf Stream could be Melting Marine Methane

Sat, 27th Oct 2012

Ben Valsler

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Changes in the Gulf Stream over the last 5000 years are destabilising trapped methane over at least 10,000 square kilometres of the US eastern margin, and if this were to be released it could cause abrupt climate changes, according to research published in the journal Nature.

Methane hydrate is a solid form of ice and methane, and is stable at high pressures and low temperatures.  They exist within the first few hundred metres of marine sediment in a region known as the Gas-Hydrate Stability Zone, or GHSZ, and represent one of the largest reservoirs of organic carbon on Earth.  Sudden release of methane hydrate has been linked to past global climate changes, such as the Palaeocene–Eocene thermal maximum (PETM).  Melting gas-hydrates have also been implicated in continental slope failures that cause underwater landslides.

The Gulf StreamTo investigate the stability of methane hydrates along the American continental shelf, Benjamin Phrampus & Matthew Hornbach at the Southern Methodist University in Dallas, Texas combined seismic data showing the depth of the GHSZ with thermal models.  They found that stable zone is deeper than predicted from models based on current ocean temperatures, and suggest that this shows methane-hydrate melting occurring in the sub-seabed.  Their results suggest that today’s warmer temperatures are destabilizing up to 2.5 gigatonnes of methane hydrate.

To try to explain this, the authors considered a number of different scenarios, and conclude that the most likely explanation is a change in either the temperature or location of the Gulf Stream – the warm current that flows across the Atlantic.

At present, it’s unclear what affect this destabilisation may have, especially as there is some debate over the role of gas-hydrates in continental shelf instability, and predictions are that it could take as much as 5000 years for this methane to escape into the atmosphere.  However, this new research highlights the importance of understanding methane hydrates, and points us towards new methods to research other important sites of methane storage where conditions are changing rapidly, such as in the arctic.

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The half life of methane in the atmosphere is about 7-10 years.

So, if the methyl hydrates are released into the atmosphere slowly, then it may be seen as an increase in atmospheric carbon dioxide, rather than a bolus of methane which may have less of an impact on the future environment.

Still, it is important to understand methane deposits, especially in "vulnerable" areas both in permafrost and shallow ocean waters. CliffordK, Sat, 27th Oct 2012

It may be desirable to mine it, if it can be done in a stable manner. http://en.wikipedia.org/wiki/Methane_clathrate#Continental
This could produce energy for consumers, and CO2 is a less potent greenhouse gas than methane.

On the pessimistic side, if a clathrate deposit became unstable, it could:

produce a burp of methane that could swallow a drilling rig

or trigger a turbidity current on the continental shelf. It has been suggested that if a turbidity current accelerates down the continental shelf at a similar rate to the velocity of a tsunami (which are faster in deeper water), this can couple considerable amounts of energy into the tsunami.
evan_au, Fri, 2nd Nov 2012

The PETM is a fascinating episode as (I think) it is the only warming event where increase in CO2 levels preceded rising temperatures. 

This is important as other warming events - attributable to milankovitch cycles - rise in temperature preceded rising CO2 levels.  This relationship is often cited by those that do not accept anthropogenic climate change as an "inconvienient truth" in (the political) arguments about the need to cut CO2 emissions etc. Mazurka, Mon, 5th Nov 2012

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