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Friday, March 5, 2010

John Cook, Skeptical Science: New observations find underwater Arctic Shelf is perforated and venting methane

New observations find underwater Arctic Shelf is perforated and venting methane

John Cook, Skeptical Science, March 6, 2010

One of the positive feedbacks from global warming is the thawing of Arctic permafrost. This releases methane, a greenhouse gas over 20 times more potent than carbon dioxide, into the atmosphere.
Investigations into Arctic methane have tended to focus on land permafrost. However, there are also vast, amounts of methane held underwater in the East Siberian Arctic Shelf (ESAS). This encompasses over 2 million square kilometres, three times as large as the nearby Siberian wetlands, which have been considered the primary Northern Hemisphere source of atmospheric methane. Underwater permafrost acts as a lid to restrain methane stored in the seabed. Until now, it was thought the permafrost was cold enough to remain frozen. However, recent observations have found that over 80% of the deep water over the ESAS is supersaturated, with methane levels more than eight times that of normal seawater (Shakhova 2010). More than half of the surface water is supersaturated also. The methane venting into the atmosphere from this one region is comparable to the amount of methane coming out of the entire world’s oceans.

To find out what was happening in the East Siberian Arctic Shelf, field measurements, ice expeditions and a helicopter survey were conducted to measure methane levels in ESAS waters. They took 5100 samples from 1080 stations, the largest database for any ocean methane study. They found widespread supersaturation over the region. Most of the bottom waters are supersaturated and over half of surface waters are supersaturated. In some areas, the saturation levels reached at least 250 times that of background levels in the summer and 1,400 times higher in the winter.

Methane Levels in East Siberian Arctic Shelf, deep waters and surface waters
Figure 1. Summertime observations of methane levels in the ESAS. Top is dissolved methane in deep water. Bottom is dissolved methane in surface water (Shakhova 2010).
To find out how much methane is escaping into the atmosphere, they measured the flux of methane at the ocean surface. Methane levels were elevated overall and the seascape was dotted with more than 100 hotspots. A helicopter survey further confirmed this, finding methane levels were 5-10% greater at 1800 metres height. Methane is not only being dissolved in the water, it's bubbling out into the atmosphere.

Yearly flux of methane venting into atmosphere over East Siberian Arctic Shelf
Figure 2. Yearly flux of methane venting into the atmosphere over the ESAS (Shakhova 2010).
These findings tell us the large underwater permafrost "lid" over the East Siberian Arctic Shelf is clearly perforated and methane is escaping to the atmosphere. Why is this a concern? The impact of positive feedback from ESAS methane is not currently included in climate model projections. However, we can deduce the role of methane feedback by looking at past climate change. About 11,600 years ago, the planet warmed very suddenly. This corresponded with strong increases in atmospheric greenhouse gases, especially Arctic methane (Petrenko 2009, Nisbet 2009). This indicates that the permafrost is sensitive to warming temperatures, having released its methane in the past. This gives us much reason to be concerned about the trajectory of the vast methane stores leaking from the East Siberian Arctic Shelf.

Comments 1 to 10:
  1. Daisym,

    John clearly explained the mechanism through which AGW is melting arctic ice and allowing methane to be released from the benthos. It isn't that complicated. The thawing of terrestrial tundra permafrost is having the same effect.

    There is underwater permafrost because during the last ice age, sea level was lower than it is now. The permafrost was created, then it was submerged when sea level rose.

    Try googling "underwater permafrost" and you can learn all about it.
  2. KeepinItReal at 11:49 AM on 6 March, 2010
    Is there a temperature record for the water around the underwater permafrost? I would be curious to see the trends.
  3. This new work is interesting and a bit scary. It will be interesting to see if any trends are detected in the next few years. But...

    Neither of the two papers to which you have linked support clathrate methane as the primary driver of sudden warming during the Younger Dryas, although they do not rule it out as part of a larger GHG feedback. A better example for the clathrate gun hypothesis might be the PETM.
  4. Sry,

    Should be "sudden warming at the END of the Younger Dryas".
  5. There is strong evidence that the Permian Extinction Boundary-where 95% all marine life died out-was caused by the melting of methane clathrates. Anyone else just a little bit scared yet?
  6. The wikipedia article on atmospheric methane is pretty good (IMHO) and it has a table that may help to put some big picture perspective on this news. Approximately 3% of total methane added to the atmosphere is listed as coming from oceans (I'm not sure if there is now ~6% if these latest results are applied). Wetlands (including rice agriculture) account for 37%. Farm animals account for 19%. There are other contributors readers might find interesting.

    Anyway, the most optimistic thing I can think to write is that we have pleny of scope to cut back anthropogenic emissions elsewhere. Halving beef production (or trapping the gas of cows) should easily compensate for even a doubling of the amount of methane released from this area. Right?, I ask hopefully.

    Finally, does the paper indicate how sea life is responds to all this supersaturated water? Methane reacts with oxygen in the water, so presumably this region is anoxic. Right?, I ask somberly.
  7. While it is true that the amount being released now in the ESAS is small compared to the total methane release rate, the scary thing is that this area alone contains (estimated) twice as much methane as is contained in the atmosphere right now. We should be wary of such a large reservoir becoming unstable especially since the permafrost is so close to the freezing point.

    Of course we can't really say right now that the methane field is destabaliz-ING because there is no significant record. But I do think that we are at the point where any sane person would buy just a little insurance.
  8. "About 11,600 years ago, the planet warmed very suddenly."

    How fast is suddenly?

  9. doug_bostrom at 13:32 PM on 6 March, 2010
    Jerry at 13:16 PM on 6 March, 2010

    A bit long in the tooth but still useful:

    "Around 14,000 years ago (about 13,000 radiocarbon years ago), there was a rapid global warming and moistening of climates, perhaps occurring within the space of only a few years or decades. In many respects, this phase seems to have resembled some of the earlier interstadials that had occurred so many times before during the glacial period. Conditions in many mid-latitude areas appear to have been about as warm as they are today, although many other areas - whilst warmer than during the Late Glacial Cold Stage - seem to have remained slightly cooler than at present. Forests began to spread back, and the ice sheets began to retreat. However, after a few thousand years of recovery, the Earth was suddenly plunged back into a new and very short-lived ice age known as the Younger Dryas. Although the Younger Dryas did not affect everywhere in the world, it destroyed the returning forests in the north and led to a brief resurgence of the ice sheets. This map by D. Peteet shows the possible distribution of Younger Dryas cooling around the world. The main cooling event that marks the beginning of the Younger Dryas seems have occurred within less than 100 years, according to Greenland ice core data (Alley et al. 1993). After about 1,300 years of cold and aridity, the Younger Dryas seems to have ended in the space of only a few decades (various estimates from ice core climate indicators range from 20 - 70 years for this sudden transition) when conditions became as warm as they are today. Around half of the warming seems to have occurred in the space of a single span of 15 years, according to the latest detailed analyses of the Greenland ice core record (Taylor et al. 1997)."

    From this:

    A quick background to the last ice age

    More background on ice core techniques here:

    End of the Last Glacial Period Inferred from Trapped Air in Polar Ice (pdf)

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