Who ya gonna read?

> pressure decrease
Other mechanisms for that would be interesting -- post-glacial rebound would raise areas of seabed, for example.

I see Wikipedia is out of date. Someone should ... oh, nevermind.

http://en.wikipedia.org/wiki/Pingo
"pingo, also called a hydrolaccolith ..."

My decades-old church latin suggests the fancy name reflects the old explanation, still given by Wikipedia, that these mounds were caused by freezing water under the surface.

Pingos (pingoes?) had been well established as caused not by freezing water but by methane boiling out of the seabed.
http://www.google.com/search?q=pingo+methane

Acores! I didn't know that. (It's the first country on the Nature subscription drop-down.) You learn something every day.

Not so convinced by 'Bruma', though. After all that effort to get everyone to call it 'Myanmar' they're surely not trying a third alternative?

Hey, they are offering a "complimentary" subscription. I hope mine is going to say "James, you sexy beast, here is your journal".

They blew it early on.

Acores is most certainly not a country - Acores would refer to the Azores islands off the coast of Portugal, and a part of Portugal (albeit a so-called autonomous region.)

So, is this an "ooooh shit!" moment, or an observation of some paleo feature?
http://www.agu.org/pubs/crossref/2010/2010GL045184.shtml
Gas escape features off New Zealand: Evidence of massive release of methane from hydrates
Geophys. Res. Lett., 37, L21309, doi:10.1029/2010GL045184

[Alas I can't read the actual article. I'm guessing this is from the dim and distant past - otherwise, it would show up in the methane records -W]

You can read it here.

From the conclusion:

Dissociation of gas hydrates at the deepâwater BGHS
is dominantly the result of pressure decrease, which is
greatest at peak stage glaciation, due to the accompanying
â¼120 m drop in seaâlevel. The pressure effect is potentially
enhanced by the coincident arrival of warm temperature
pulses at the BGHS. The low slope angle (< 1.5°) and low
rates of modern sedimentation on the shallow southern
Chatham Rise may have provided a stable environment that
preserved the GEFâs over multiple glacialâinterglacial cycles.
If similar features formed globally, then the cumulative
release may have significantly increased the global methane
supply into the ocean and atmosphere at the peak of glaciations
and potentially contributed to the rapid transition to
warmer postâglacial conditions (e.g. clathrateâgun hypothesis
[Kennett et al., 2003]).

I italicized the bit that makes it appear to be talking about the past and ... well ... the far-off future assuming the next ice age happens.

[Aha, thanks. I'm immeadiately struck by one of the refs, to "Mobil International Oil Company, 1979" which clearly means the whole thing is unreliable :-)

As you say, they interpret this as due to LGM sea level lowering destabalising the clathrates (though they do point out that warming might do it too). So that might well mean that we don't care today. They are also a bit cautious in the methane release numbers; one GEF might be 3% of total current annual release, so (for example) one occurring every year for 1,000 years might not matter much. Would be interesting to see them better dated (cored?) and correlated to the global methane record -W]

Raising the threat level color by one or two angstroms:

http://icesjms.oxfordjournals.org/cgi/content/abstract/fsn008v1

"... Until recently, it was assumed that methane in the atmosphere came either from active wetlands or from hydrates buried at least 200 m under the seabed. Having regard to the pressure and temperature gradients below the seabed, methane hydrate would have been unstable at any lesser depth and would have already been discharged: outgassing would not resume until conditions changed, causing destabilization. In past outgassings, deeply buried hydrates may have been destabilized because of rising temperatures in intermediate-level ocean waters caused by changes in the thermohaline circulation (Kennett et al., 2000). It seems likely now that global warming has started and that much (most?) atmospheric methane comes from the permafrost under the Arctic Ocean's continental shelf and the adjacent coastal plain. These two areas form a continuous expanse of surface that is partly submarine and partly subaerial. For example, some methane is being emitted now, from low (10â35 m) submarine hills on the floor of the Beaufort Sea, at depths of from 20 to 200 m (Blasco et al., 2006). The buried hydrate appears to be unstable only metres below the seabed. It is unknown whether and where methane outgassing is happening elsewhere.

To return to the Beaufort SeaâMackenzie Delta region, the submarine hills resemble pingos, the small ice-cored conical hills, seldom more than 40 m high, found in thousands on the adjacent coastal plain tundra from Point Barrow, Alaska, to Cape Bathurst, Northwest Territories. The submarine âhillocksâ are called pingo-like features, or PLFs. It has been discovered (Paull et al., 2007) that streams of methane bubbles emerge from the summits of some of the PLFs, from their methane hydrate cores. The cores are being forced up by gas pressure from below. How much methane is produced, and how long this has been going on, is not yet known. It could have begun quite recently. The permafrost has been warming, gradually and with some interruptions, ever since the last glaciation ended, and the hydrate it contains may have started to disintegrate at a threshold temperature reached not long ago.

It also seems likely, although this is (again) highly speculative, that terrestrial pingos may be, or may become, methane sources. The manner of their formation (Mackay, 1994) indicates that they originated, and still originate, in shallow lakes on land, and it is natural to suppose that PLFs began as terrestrial pingos that were submerged by the rising sea level as the ice sheets melted. However, an argument against this is that pingos sinking into a rising sea would be expected to be destroyed by wave erosion while they were at shoreline level rather than persisting as hills. Nevertheless, the spatial proximity of three hundred Beaufort Sea PLFs and the densest cluster of pingos on land (on the Mackenzie Delta and Tuktoyaktuk Peninsula) seems more than a coincidence. Altogether, more than 2000 pingos are found on the Arctic coastal plain (Mackay, 1988). Whether they will turn out to be, or to become, methane sources remains to be seen. ..."

(Compare "bubbles emerge from the summits of some of the PLFs, from their methane hydrate cores" to Wikipedia's explanation for small craters noted atop the hills.)