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New observations find underwater Arctic Shelf is perforated and venting methane

Posted on 6 March 2010 by John Cook

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 to 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 it's 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.

Update 7 Mar 2010: Real Climate offer some good perspective on methane feedback which echoes the theme in CO2 is not the only driver of climate:

"CO2 is plenty to be frightened of, while methane is frosting on the cake. Imagine you are in a Toyota on the highway at 70 miles per hour approaching stopped traffic, and you find that the brake pedal is broken. This is CO2. Then you figure out that the accelerator has also jammed, so that by the time you hit the truck in front of you, you will be going 80 miles per hour instead of 70. This is methane. Is now the time to get worried? No, you should already have been worried by the broken brake pedal. Methane sells newspapers, but it’s not the big story, nor does it look to be a game changer to the big story, which is CO2."

Update 12 Mar 2010: Thanks to Charles Brock who alerted me to a paper published mid-2009, Observational constraints on recent increases in the atmospheric CH4 burden (Dlugokencky 2009). Key results (noting that this is based on data ending in 2008):

Measurements of atmospheric CH4 show that, after a decade of near-zero growth, globally averaged atmospheric methane increased during 2007 and 2008... Near-zero CH4 growth in the Arctic during 2008 suggests we have not yet activated strong climate feedbacks from permafrost and CH4 hydrates.

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Comments 51 to 70 out of 70:

  1. #46 chriscanaris, my understanding of the term "Socratic dialogue" matches what the short wikipedia entry says: discussion of moral or philosophical problems, answering and asking questions. As a method of rational thinking, it's great.

    But scientific questions are not answered by dialogue. They are answered by data. Socrates was not an experimentalist. The Socratic Method was not the Scientific Method. It seems to me that you have redefined Socratic dialogue, although we seem to agree that the scientific method is the way forward to answering many questions.
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  2. CBDunkerson wrote: "the reason that surface concentrations (and thus atmospheric release) of methane are highest in shallower waters is BECAUSE they are shallow... there is less water for the methane to disperse through.


    As to geological processes producing methane... look at the ocean floor map. What could possibly produce that much methane that consistently over that large an area? We're not seeing isolated spots of methane release, but rather an entire region producing methane. That clearly points to release from the permafrost due to warming."

    CBD: The maps of methane concentrations are actually not that consistent over the area, whether measured near the sea bed, in surface waters or in the atmosphere. The maps show elongated N-S stripes*, whereas the main trend of the bathymetry is roughly at right angles to this. However, I do think that melting permafrost is the most likely and, perhaps, the only explanation for the observed methane; I would just like to better understand the influence, if any, of the deep geology.

    I note that the authors report using a chromatograph to analyse the gas but they don't mention observing any ethane or other alkanes. They do say that they intend to do some isotopic work in future.

    *The N-S trends in their maps actually look a little suspicious to me and I wonder to what extent they have been influenced by the orientation of some of the sampling stations along N-S transects (Fig 1A) and the authors' use of a Kriging gridding process. The coastline on Fig 1A is different to those shown on 1B,C and D, particularly for the islands, but this is just drafting error. None of this is likely material to their main point but I wouldn't be surprised to see it picked up and blown out of proportion by a certain mining engineer.
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  3. In 2007 Shakhova et al wrote,

    "Until recently, due to slightly negative annual temperatures within the water column and the lid-type coverage of shelf sediments by sub-sea permafrost, old organic carbon buried on the Siberian Arctic shelf was considered completely isolated from the modern carbon cycle."

    So it seems fair to say the observed venting is a new phenomenon.

    Shakova et al 2010, wrote,


    The East Siberian Arctic Shelf covers a similar area to the Siberian traps which has been linked to a large increase in GHG's in the past.

    As the potential volume of GHG's from the ESAS is so large, perhaps similar to levels released by the Siberian traps, isn't it reasonable to suggest that the effects of ongoing and near complete venting of ESAS Methane will be similar to the effects of the Siberian traps event?
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  4. 2003: (emphasis added)

    "The National Oceanic and Atmospheric Administration (NOAA) reports that atmospheric concentrations of
    methane, a potent greenhouse gas, have begun to level out AFTER TWO CENTURIES OF INCREASES. In a November 17
    press release, NOAA reports that scientists are still trying to determine what this means."
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  5. Cowboy at 16:52 PM on 8 March, 2010

    On a romp, posting years-old information, cowboy. That article you cited is of course from 2003; the rise in methane long since resumed.

    Your point?
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  6. Clathrates ...
    "The CSIRO and other scientists around the world examined ice cores in Greenland and found that during the Younger Dryas event between approximately 12,800 to 11,500 years ago the increase in atmospheric methane of that time was not sourced from clathrates under the ocean "but from ecological sources such as wetlands""
    "We know that emissions of methane are increasing now and that some sources might emit even more with warming, causing a positive climate feedback, or amplification. But this finding suggests that the clathrate source is less susceptible than recently feared,” Dr Smith says."
    "Researchers at the University of California, Santa Barbara have discovered that only one percent of this dissolved methane escapes into the air – good news for the Earth's atmosphere."
    "We found that the ocean has an amazing capacity to take up methane that is released into it – even when it is released into shallow water," said Valentine."
    "This lead the authors to hypothesize that most of the methane is transported below the ocean's surface – away from the seep area. THEN IT IS OXIDIZED BY MICROBIAL ACTIVITY."
    I recommend in Environmental Microbiology a lot of paper about: system - archeons - sulphate bacteria ...

    Clathrates are irrelevant to the climate - says reviewed science ...
    A level (practically constant for a circa decade) of methane in the atmosphere is here:
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  7. Arkadiusz Semczyszak,
    no question that at current temperature level wetlands are the major contributors. The problem is that in a more distant past, when the temperature was at level toward which we are heading, there has likely been significant contribution from clathrates. The facts the methane from clathrates didn't play a major role at the end of the Younger-Dryas does not allow you to claim that "Clathrates are irrelevant to the climate" tout court.
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  8. Tundra - Schlesinger (1991) and Leith and Whittaker (19975) - the accumulation of C = 0.2 g/y C, content - 21.6 kg/m2. Wetlands - 15.3 g/y and 68.6 kg/m2 (!). Melting permafrost is "good news" for the L.-V. model oscillations: CH4 - biocarbon.
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  9. "Clathrates are irrelevant to the climate" - but this claim is more likely than the opposite ...
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  10. Of course, would be: soil of tundra
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  11. I recommend in Environmental Microbiology ...
    e.g. - J. J. Moran et. al. 2007. "Methyl sulfides as intermediates in the anaerobic oxidation of methane".
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  12. Evidence that the ESAS venting is a recent occurance,

    From ‘The Independant’,

    “The preliminary findings of the International Siberian Shelf Study 2008, being prepared for publication by the American Geophysical Union, are being overseen by Igor Semiletov of the Far-Eastern branch of the Russian Academy of Sciences. Since 1994, he has led about 10 expeditions in the Laptev Sea but during the 1990s he did not detect any elevated levels of methane. However, since 2003 he reported a rising number of methane “hotspots”, which have now been confirmed using more sensitive instruments on board the Jacob Smirnitskyi.”
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  13. Andy S, actually if you compare the sea floor and sea surface maps (it is more difficult with the atmospheric, which uses a different color scheme) I think you will see that the difference between the two IS 'at right angles'. For instance, high concentrations of methane are retained at the surface along the shallow coastline, but drop to lower concentrations (compared to the sea floor values) further out to sea. The only significant exception to that trend being the high concentrations maintained in roughly the middle of the map... to the north and south of an island which likely sits on an elevated ridge.

    As to the north south banding... my first guess would be undertow currents. Relatively warm water comes in to the coast, flows under, causes the methane to melt, and pushes it northwards.
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  14. For what it's worth (not necessarily much) I'd agree with Andy S that the odd N-S directionality in the figures looks like an artifact of the interpolation of sparse data (via kriging, IDW, or whatever).

    Look at Fig 1A in the paper (which shows the distributions of stations sampled). There's a much greater sampling density along the coast, and along certain N-S or other transects. Meanwhile, there are some isolated points (e.g., 170E, 73N) that seem to have a disproportionate influence on the interpolation results.
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  15. "Cowboy at 16:52 PM on 8 March, 2010


    Your point? "

    1. Methane, 20 times more effective as CO2 with respect to 'greenhouse' effect, has been increasing in the atmosphere for 200 years, but we want to blame CO2 for warming?

    2. Obviously, methane doesn't need any man-made global warming to be released into the atmosphere.
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  16. CBD: I do agree that where there are higher methane levels in the bottom water (incorrectly, I think, labelled "deep water" on the figure captions on this site) the surface water amounts tend to be relatively less in the deeper water furthest from the shore. I guess this is due to greater oxidation of the methane as it rises in the deeper water.

    The relationship I was looking for, and couldn't see, is more methane in the bottom water in the shallower area, which is what I would expect to see if the water was warming from the top down. However, as you suggest, there may well be currents that complicate the story.

    I don't doubt the overall thrust here, I'm just struggling to understand it better.
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    Response: The label "deep water" was intentional. I noticed in the paper, they label it "bottom water" but in the press release, they call it "deep water". I just went with the phrase that would make more sense to the average person. It's a judgement call - do you go with the scientifically more precise term or the term that makes more sense to the public?

    Overall, the forcing from methane is +0.48 watts/m2 while that from CO2 is +1.66 watts/m2 (see John's post from last year, here). So while methane is a substantial player in the current radiative imbalance, it's definitely of less importance than CO2 at least for now.

    You're right that there are natural methane sources such as wetlands (175 Tg/year), termites (20-30 Tg/year), and biochemical processes in the oceans (10 Tg/year). However, anthropogenic emissions (from fossil fuel production, landfills, rice paddies, livestock, landfills, etc.) have more than doubled the natural, pre-agricultural background methane flux. See here for more details.

    Before humans began modifying the environment, atmospheric methane stayed within the range of 400-700 ppb through repeated glacial/interglacial cycles, for at least the past 650,000 years (see Wolff and Spahni 2007). It's now over 1700 ppb. That increase is due to our agriculture, industry, and land use impacts.
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  18. Methane emissions from Wetlands etc have dramatically risen in comparison to levels over the last 1000 years, doesn't this show that current temperatures are unprecedented over the period?
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  19. Whilst this is not specifically related to the artic ice methane release it is related to methane. Does anyone have any scientific evidence that supports the global catastrophe theory of massive methane release imminent in the Gulf of Mexico due to the BP Deepwater Horizon oil drilling accident.
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  20. Some interesting recent developments on the methane clathrate/PETM front.

    1. From GEOLOGY (Abstract only available):
    "Changes in ocean circulation have been proposed as a trigger mechanism for the large coupled climate and carbon cycle perturbations at the Paleocene-Eocene Thermal Maximum (PETM, ca. 55 Ma). An abrupt warming of oceanic intermediate waters could have initiated the thermal destabilization of sediment-hosted methane gas hydrates and potentially triggered sediment slumps and slides. In an ensemble of fully coupled atmosphere-ocean general circulation model (AOGCM) simulations of the late Paleocene and early Eocene, we identify such a circulation-driven enhanced intermediate-water warming. Critically, we find an approximate twofold amplification of Atlantic intermediate-water warming when CO2 levels are doubled from 2× to 4× preindustrial CO2 compared to when they are doubled from 1× to 2×. This warming is largely focused on the equatorial and South Atlantic and is driven by a significant reduction in deep-water formation from the Southern Ocean. This scenario is consistent with altered PETM circulation patterns inferred from benthic carbon isotope data and the intensity of deep-sea carbonate dissolution in the South Atlantic. The linkage between intermediate-water warming and gas hydrate destabilization could provide an important feedback in the establishment of peak PETM warmth."
    CO2-driven ocean circulation changes as an amplifier of Paleocene-Eocene thermal maximum hydrate destabilization

    2. From Philosophical Transactions Of The Royal Society A (Abstract only available):
    "The plausible range of carbon mass input, approximately 4000–7000 PgC, strongly suggests a major alternative source of carbon in addition to any contribution from methane hydrates. We find that the potential range of PETM atmospheric pCO2 increase, combined with proxy estimates of the PETM temperature anomaly, does not necessarily imply climate sensitivities beyond the range of state-of-the-art climate models."
    A Palaeogene perspective on climate sensitivity and methane hydrate instability

    3. From a poster presentation at the EGU, 2010
    "Hyperthermal climate events are geologically brief (~10-100kyrs) transient periods of marked global warming associated with prominent negative carbon isotope excursions and deep-sea carbonate dissolution. They are most likely the result of massive injections of isotopically light carbon into the ocean-atmosphere system. One plausible source of isotopically light carbon is a widespread dissociation of continental slope, sediment-hosted methane gas hydrates. Proposed triggers for the dissociation of such deep-water hydrates include a pronounced (~4ºC) warming of intermediate to deep waters driven by changes in global overturning circulation (Dickens et al., 1995).

    The most prominent hyperthermal event of the Ceonzoic is the Paleocene Eocene thermal maximum (~55Ma; PETM)."

    We show modelling results which support the hypothesis that Eocene hyperthermals could be paced by orbital variations. The mechanism for this forcing is orbitally induced switches in ocean circulation, which lead to non-linear intermediate ocean warming, with the possibility of resulting destabilization of methane gas hydrates. The switches in circulation are associated with high eccentricity and obliquity and maximum seasonality in the Northern Hemisphere."
    Poster Source:
    Is There An Orbital Control On Eocene Hyperthermals?

    Apologies for no links to the full articles (both paywalled). I've requested the articles through my employer library; will offer up a deeper dish when I get them.

    The Yooper
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