Methane Hydrate Release Now Underway In Beaufort Sea Pingoes - GRL

[hatrack]

GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L01603, doi:10.1029/2006GL027977, 2007

Origin of pingo-like features on the Beaufort Sea shelf and their possible relationship to decomposing methane gas hydrates

Charles K. Paull and William Ussler III

Monterey Bay Aquarium Research Institute,
Moss Landing, California, USA

Scott R. Dallimore

Natural Resources Canada,
Sidney, British Columbia, Canada

Steve M. Blasco

Natural Resources Canada,
Dartmouth, Nova Scotia, Canada

Thomas D. Lorenson

U.S. Geological Survey,
Menlo Park, California, USA

Humfrey Melling

Fisheries and Oceans Canada,
Sidney, British Columbia, Canada

Barbara E. Medioli and F. Mark Nixon

Natural Resources Canada,
Ottawa, Ontario, Canada

Fiona A. McLaughlin

Fisheries and Oceans Canada,
Sidney, British Columbia, Canada

Abstract

<1> The Arctic shelf is currently undergoing dramatic thermal changes caused by the continued warming associated with Holocene sea level rise. During this transgression, comparatively warm waters have flooded over cold permafrost areas of the Arctic Shelf. A thermal pulse of more than 10°C is still propagating down into the submerged sediment and may be decomposing gas hydrate as well as permafrost. A search for gas venting on the Arctic seafloor focused on pingo-like-features (PLFs) on the Beaufort Sea Shelf because they may be a direct consequence of gas hydrate decomposition at depth. Vibracores collected from eight PLFs had systematically elevated methane concentrations. ROV observations revealed streams of methane-rich gas bubbles coming from the crests of PLFs. We offer a scenario of how PLFs may be growing offshore as a result of gas pressure associated with gas hydrate decomposition.

<2> Gas hydrate is a solid phase comprised of water and low-molecular-weight gases, usually methane, that forms within sediments under conditions of low temperature, high pressure and adequate gas concentration. On a worldwide basis, gas hydrates have been identified in deep water marine settings and in the Arctic associated with areas with thick permafrost . Because in nature these deposits exist close to their pressure-temperature equilibrium, a modest increase in formation temperature, or decrease in pressure may induce decomposition. In this case formerly gas-hydrate-bound methane will be released with the potential for gas migration to the surface, and ultimately the atmosphere. Because methane is a potent greenhouse gas, the fate of decomposing gas hydrate is of considerable interest in global warming scenarios.

<3> This paper focuses on evidence of degassing from decomposing Arctic gas hydrate deposits beneath the southern Beaufort Shelf. This area is arguably one of the most gas-hydrate-rich regions in the Arctic . During the Pleistocene much of the Beaufort Shelf was an emergent, unglaciated coastal plain exposed to very cold mean annual surface temperatures , which aggraded thick permafrost. The geothermal regime is conditioned by this permafrost interval and as a result methane hydrate may be theoretically stable to depths as great as 1500 m . Marine transgression during the Holocene has caused much of the Beaufort Shelf to be inundated by relatively warm marine and estuarine waters. This has imposed a step change from mean annual land surface temperatures perhaps as low as −20°C during glacial times to present bottom water temperatures which are no colder than −1.8°C. The consequence of this warming is to reduce the vertical extent of both permafrost and the stability zone in which gas-hydrate-bearing sediments may occur. Because of the slow process of heat conduction, the transient effects of the transgression are still occurring . Thus, methane gas release, if it is occurring, should be continuing today.

EDIT

<10> ROV dives with comprehensive spatial coverage over the PLFs were carried out at Pingo Z and Admirals Finger Pingo B. Gas release was seen from the crest of these PLFs with discrete bubbles emanating from ~5 cm diameter holes. Multiple sites were visible in the ~10 m2 ROV field of view. No shimmering water or other evidence of flowing water, indications of exotic fauna, bacterial mats, or authigenic carbonates were seen. The ROV dives and multibeam images show that PLF crests are crossed by linear grooves apparently associated with ice scour . A gas sample was collected by ROV from a bubble stream on the crest of Pingo Z in 18 m of water. By timing the filling rate of an inverted funnel a flux rate of ~5 L hr−1 was estimated. The gas is predominantly methane (δ13C = −76.6‰ and δD = −179‰), which is similar to the other gas samples from PLF, and contains only 0.93 percent modern carbon (pMC).

EDIT

Much more in article, but subscription service only - no link.

On edit: releases measured in this study are small, but the propagation of far warmer water is unlikely to slow anytime soon, and the paper does provide a plausible mechanism as to how the PLFs are a temperature response and also provide a means for further hydrate off-gassing.

[AnneD]

1. OH

HOLY SHIT! We are so screwed......All we need is methane in the enviroment.

[Porcupine]

10. SHIT!!

That is BAD NEWS GEORGE!!

It would be nice to live on a planet with a sane life form in control. The current dominent species seems to be bent on suicide.

[hobbit709]

2. When it comes to greenhouse gases

Methane makes CO2 look like an amateur.

[hatrack]

3. The good news is that it doesn't last nearly as long

The bad news, of course, is that it's about 25X more efficient at trapping infrared.

I think there's the potential for things to get really interesting in and around the Beaufort Sea.

[razors edge]

4. I always thought

Paris Island smelled funny. I just thought it was the combination of green wool socks and leather boots.

[GliderGuider]

5. I'm thinking ahead to the next IPCC report in a few years

The main things areas that were fuzzy in this one related to dynamic processes - specifically glacial dynamics and positive feedback loops. I expect the science in these areas to clarify a lot over the next five years, and given what we've found so far I don't expect the results to be favourable.

I've always maintained that Peak Oil presents a more immediate danger to industrial civilization, but that it would interact with climate change to affect marginal countries first and hardest. While I still think that, I'm no longer so unequivocal in my view that it is the indisputable lead element of the Problematique. Certainly the potential exists for climate change to have civilization-scale effects in the same time period as oil depletion (say 10 to 20 years). That will make adaptation to an oil-scarce world much more difficult over the next 30 to 50 years.

[phantom power]

6. I got the impression that the IPCC report sort of cut off at 2005 input.

Which makes sense, considering that when you are compiling a report, you have to stop changing your content at some point. But things are developing rapidly on the ground now. Lot of new information (none of it good) has come to light in the last year or so.

[htuttle]

7. Well, there's the other shoe dropping -- or one of them, anyway

There have been so many shoes dropping, I'm thinking that fate is a centipede...

[phantom power]

8. or maybe just Imelda Marcos.

[intaglio]

9. You know I am really thankful that my house

is above the 100m (330 foot) contour. eom