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Subcap Methane Feedbacks, Part 1: Fossil methane seepage in Alaska

Posted on 28 November 2012 by Andy Skuce

As permafrost thaws, methane is released as the vegetable matter in the soils decomposes. This methane bubbles to the surface in lakes and ponds and accumulates under the ice in the wintertime. New research has shown that the most vigorous methane seeps in Alaska are fed also by methane emitted by thermal decomposition of organic matter in deeper and much older sediments. Continuous permafrost acts as a top seal to this fossil methane, preventing it from reaching the surface and, as global warming melts and perforates this cap, we can expect the pent-up gas to be released more quickly. This source of methane, released from traps under the permafrost, is a potential third source of methane feedback in the Arctic, in addition to permafrost soils and methane hydrates. 

One of the big unknowns in forecasting the course of climate change is anticipating how the Earth’s carbon cycle will respond to the coming man-made increase in temperature. The carbon cycle describes the many processes through which carbon flows between stocks of the element in the atmosphere, the oceans, the rocks, the soil, and in plants and animals. The Earth's most sensitive place to changes in the carbon cycle is the Arctic. Not only is this the region with the fastest changing climate and some of the largest stores of carbon, but even small temperature changes there will produce large effects as ice and soils that have been frozen for thousands of years begin to thaw.

Figure 1. Schematic diagram of the many ways that greenhouse gasses can be released as a warming climate in the Arctic leads to collapse of the cryosphere. Most of these will be covered in this series of articles. Graphic by John Garrett.

The permafrost is essentially an enormous freezer, locking away vast quantities of plant matter from participation in biological processes. When global warming removes this vegetable purée from the Holocene refrigerator and places it on the Anthropocene compost heap, it will rot and release carbon dioxide and methane. The infra-red absorbing properties of these gasses will, in turn, cause further global warming.

recent study by Schuur and Abbott has predicted that, under the four representative emission pathways (to be used for the IPCC fifth assessment), some 232-380 billion tonnes of CO2 equivalent will have been emitted by 2100 from thawing permafrost. That is roughly equivalent to eight to twelve years of emissions from fossil fuel combustion at current rates. A recent modelling study has shown that feedbacks from emissions of carbon dioxide alone (i.e., ignoring methane emissions) from thawing permafrost will increase warming by an average of one-quarter of a degree Celsius by the end of this century.

A second potential source of Arctic methane is from the destabilization of methane hydrates, an ice-like combination of water and methane that forms, and is stable, at a combination of low temperatures and high pressures. Because the largest documented deposits of hydrate are deeply buried, under a few hundred metres of water or under thick permafrost, most scientists believe that it will take time—centuries or even millennia—before they are destabilized by global warming in a major way. Nevertheless, because the quantities are so huge—the amount of carbon in hydrates may be twice as high as the carbon in fossil fuels— and because the mechanisms of destabilization are not well understood, methane hydrates are the subject of anxious attention.

Doffing the cryosphere cap

As if two big sources of Arctic greenhouse gas feedback were not enough, research by Katey Walter Anthony and three colleagues (WA12, paywalled; see also this BBC report and this RealClimate article), recently published in Nature Geoscience, has identified a third: geological or fossil methane seeping out of sediments deep from beneath the permafrost. In this subcap seepage the permafrost acts, not just as an ice-locker containing carbon, but also as an impermeable cap impeding the upward motion of gas from deeper sedimentary rocks to the surface. As this seal thaws and becomes perforated, it allows gas to seep more quickly to the surface.

WA12 identified two additional types of subcap seep and these will be discussed in part three of this series. One involves retreating glaciers and ice caps that cause the crust to bend from the change in loading; this flexing can reactivate faults and open fractures, allowing them to act as conduits for deep gas. The other type is caused in a different way by retreating ice sheets that expose organic matter that was previously overridden and buried during an earlier glacial advance. All of these processes involving melting permafrost and retreating glaciers are lumped together as “cryosphere cap” phenomena.


Figure 2. This is part of Figure 4 in WA12. It is a schematic north-south cross-section through Alaska, illustrating: the topography and glaciers; the depth and continuity of permafrost (light blue) and yedoma (grey; wind-blown silts, rich in organic matter); water bodies (blue) and melt bulbs (white) in the permafrost; coal seams, faults and conventional hydrocarbons; and methane hydrates under the North Slope.

Observing and sampling Alaskan seeps

Katey Walter Anthony and her colleagues conducted aerial surveys in Alaska, searching for evidence of seeps in frozen Arctic water bodies (lakes, rivers and fjords).They backed up this reconnaissance work with ground observations by measuring seep rates and taking samples of the bubbling-up gas. Faster-bubbling seeps stir up the water more, keeping the holes in the ice on the surface of the water bodies open longer during the winter. They are thought to be associated with gas coming from below the permafrost and are called "subcap seeps". In contrast, superficial seeps (from biological processes within the permafrost itself) would be expected to bubble-up more slowly and form smaller holes in the winter ice. These holes freeze over more quickly, trapping methane bubbles within and below the ice.


The video shows some examples of superficial methane seeps—and the eyebrow-singeing fun that can had be with them.

There are a variety of analytical techniques available to determine the age and origin of the methane gas.

First, unstable carbon-14 isotopes can determine the age of the organic material that was the origin of the methane. Most of the subcap methane seems to be more than 50,000 years old, older than the last glacial maximum and perhaps much older.

Second, stable isotope ratios of carbon-12/carbon-13 and hydrogen/deuterium provide a fingerprint of the way the methane was generated, with biological methane being more depleted in the heavier isotopes than the fossil/geological methane, which was formed at depth by chemical processes at higher temperatures and pressures. Much of the subcap methane appears to have had a deep source like this.

Third, measuring the proportion of ethane and propane in the gas samples allows them to be compared with samples of gas from nearby natural gas wells; again supporting the idea that the subcap methane is of a deep, fossil origin. Some of the subcap gas showed signs of mixing with shallow biological gas as it made its way to the surface. The superficial seeps, on the other hand, were exclusively of biological origin.

These factors, taken together, strongly suggest that the most active seeps in Alaska result from the bubbling up of methane from deep, old geological origins rather than methane produced by biological decomposition of younger organic matter. This is important because this fossil methane provides a third source of potential greenhouse gas feedback in the thawing Arctic, in addition to the permafrost and methane hydrate sources.

Geographical distribution of the subcap seeps

Figure 3. An extract from Figure 2 in WA12, showing the distribution of subcap seeps in relation to permafrost regions; present and past glaciations; and locations of coal and petroleum deposits. The legend was edited from the original to exclude references to features not shown in this extract. Original figure is here.

If the gas in the fast seeps does indeed come from deep geological sources, then the distribution of these seeps should show a pattern. For example, the large subcap seeps related to permafrost should be located in the continuous permafrost area of northern Alaska, in areas where the geography and near-surface geology allows the formation of thaw bulbs, or near the boundary between the continuous and discontinuous permafrost. In the discontinuous permafrost area of central Alaska, seeps should be predominantly superficial, with subcap seeps being small and rare. Also, subcap seeps need to be fed from below, which means that they should overlie sedimentary basins that contain petroleum source rocks or coal. Generally speaking, this is borne out, as shown in Figure 3.

Surface seeps of fossil methane (and oil) have long been recognised in Alaska and elsewhere around the world. The contribution of Walter Anthony and her colleagues is to have quantified the Alaska gas seeps and to have provided us with evidence and criteria to distinguish fossil methane seeps from seeps of younger, biological methane that occur in the areas of thawing permafrost. In the next part of this series, we'll look at the significance of the Alaskan subcap seeps in the context of other permafrost-related seeps of methane and geological sources of methane in other parts of the Arctic and compare them to geological seeps observed elsewhere on the planet.

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Comments 1 to 25:

  1. That Figure 1 by jg is very cool!
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  2. Agreed, Dana: As a geologist, I've been worried about the 'clathrate gun' for some time, and this also figures into my worry. The future for our grandkids and beyond is beginning to look *really* not rosy. The graphics, and the message of this post are well-done and *extremely* upsetting.
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  3. Very informative post. My thumbs up to Fig 1 as well.
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  4. I had never thought about the process of glacial retreat causing a release route for deeply buried methane; I had only considered year ground permafrost that is more subject to warming. A rather worrying discovery indeed
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  5. "The future for our grandkids and beyond is beginning to look *really* not rosy." Isn't this denial by dispalcement in time? As in things in terms climate aren't exactly rosy already. Another flood about to hit Italy, 3rd devastating set of floods in less than a month there, the UK last week (being blamed on flood defences despite these having been upgraded tremendously in the last 30 years), and California weather event about to happen, record drought in USA building and so on and on. As for methane, additonal Arctic releases that are already happening, methane is on the rise again and all the extra is coming from the Arctic. The times of "not rosy" seems like it is now not tomorrow. As for our ancestors what are they going to say about us if we actually leave any at this rate! The car was important than humanity?
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  6. Sub-cap methane is news to me - very unwelcome news. It was bad enough contemplating biological methane and clathrates, without throwing geological methane into the mix. Correct me if I'm wrong, but isn't methane implicated in the loss of atmospheric ozone? We are not only getting hotter, but also more irradiated. The depth of our collective stupidity is breath-taking!
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  7. David Archer has mentioned that warming ocean releases C at the end of glacial cycles in Pleistocene, and that we don't know the precise mechanism of this phenomenon which ultimately sparks the interglacials. At least that's the state of David's teachings few years ago (2006 in his "Understanding the Forecast" book). I wonder, if given those recent studies about methane seepage through thawing permafrost, we might now point the mechanism of said carbon release. As the permafrost warms (more than the rest of the globe through arcgtic amplification) so does the methane seepage rate releasing the needed amount of carbon... That's of course happening at a slower rate (millenia) as opposed to centuries now in Anthropocene.
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  8. ranyl@5, let me restate that which I clearly did not do a good enough job the first time: I agree with your take on it all. Here's what I meant: Yes, today's situation looks pretty grim, but compared to the grimness which appears to be in store for our crandchildren and beyond, looks VERY grim indeed. Somewhere I read a line that went something like this; our grandchildren, rather than enjoying their retirment, will likely be in a fight for survival. And yes, future generation are going to look back *pretty* darned unfavorably at the prior ones: heck, I do that even now, at the generations that preceded me. Two generations back had something like an "excuse" for not stewarding the planet better; my generation has little excuse for the violence it has brought down upon the biosphere.
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  9. What percentage of Siberia is covered by glaciers?
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  10. Villabolo: very little of Siberia is glaciated, just in some scattered mountain ranges. It's too dry, basically, which is why no great continental ice sheet formed in eastern Siberia during the last glacial maximum. But there's plenty of frozen ground there, of course.
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  11. chriskoz@7 I think that the carbon isotope signature of the CO2 in ice cores points to a predominantly marine origin (ie, isotopically heavier) of the extra CO2, rather than a fossil carbon, soil carbon or methane hydrate carbon origin (all isotopically lighter).
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  12. Do Methanogens increase their metabolic rate as soil temperatures go up? I'm guessing that they should since every other microbe does. Another feedback loop?
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  13. villabolo, here are a few references...I tried to read them for the info you requested, but my eyes glazed over...;)
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    Moderator Response: [DB] Hot-linked referenced papers.
  14. "Here's what I meant: Yes, today's situation looks pretty grim, but compared to the grimness which appears to be in store for our crandchildren and beyond, looks VERY grim indeed." Fair enough vroomie it is just an ever common theme that the time of change is tomorrow. Only grim if we don't act now and appropriately to the actual scale of the problem. 350ppm is a metaphorical 1000 miles away and still means basically 2C if the climate sensitivty paper in nature is anything go by, considering we are actualy at 460ppm already (CO2e) and we have been shaded by SO2 for the last 50 years, and the unbrella is the same size now as it was 1980. Don't we need to come together, stop using so much excessive power and plan a sustainable informed, concerned and equitable future through an adaptive transformation away from fossil fuels, excess resource extraction, gross inequality, unnecessary wars, waste production, and creating toxic landscapes and show our decendants what humanity humankind is capable of or do just hope that the overwhelming evidence is somehow wrong or that some divine intervention is on the way? For at the current time these very early signs of climatic change are very alarming and much worse than expected or predicted, and therefore all solutions put forward so far are off the table and the stakes seem to rise with every study published. We have no more carbon to risk safely (I say that loudly and with concerned conviction) and therefore every ounce extra has to be wisely spent and very carefully considered and only spent for essential needs. We also have no room to stress the world's eco-systems further, (everything else humanity is doing has induced a mass extinction already), indeed more than that the earth's eco-system need intensive care (and we are capable of this) and global warming a known previous killer has only just started albeit at rate that is unprecedented and it is the rate that counts. Don't we need to take this with the gravity it deserves and stop using fossil fuels asap? (I do live a low carbon lifstyle but I could do better) Isn't the quickest way to do this, is to just stop using them? Leave the car in garage, stop flying, turn the thermostat down, wear more clothes, stop consuming, have a gift free christmas (share friendship not gifts for everyone's sake?), eat locally and sesonally and be creative about it, to let this be the fun it can be. However we also need to assess every solution objectively, is something called green always actually environmental enhancing? For example PV panels are a toxic waste within 20-30 years, releases tri-nitrofloride to make (a very potent GHG), are highly energy intensive to manufacture requiring high grade silicon, need rare chemicals that are toxic to make and need mining and extensive processing to get, are highly inefficient, are black if placed in the desert (albedo), and are not very effective in wet cloudy climates were lots are found, so are they a sensible solution or a mal-adaptation? Tropical dams and probably higher latitudes ones release massive amounts of methane (ongoing) and disrupt whole eco-systems for ages (look at the Nile delta), silt up, require huge amount so of materials to make, large maintainence rquirements and overall and are more GHG intensive and eco-system disrupting than fossil fuels!(not advocating fossil fuls by saying that, just seing large scale hydro power for what it is) With no carbon to spend and eco-systems on the brink don't we need the lowest carbon solutions that provide longer term sustainability,(even if that means much much less and even intermittent power or using sail ships built with today's understanding for sea trading) and that also enhance the environments eco-systems arround us, rather than being an eventual toxin to them as we need our eco-systesm to become larger carbon sinks despite the nitrogen fertilization that has occured in the last 50years being taken away!!? The diagnosis is grim if we do nothing or the wrong thing without proepr assessments, yet the treatment however is simple, come together in purpose and stop ignoring the truth of the situation. No one has a get out of jail free card in this game, it really is all together or no all at all. We need to relocate New York. Greenland?
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  15. ranyl@14... "Don't we need to come together, stop using so much excessive power and plan a sustainable informed, concerned and equitable future through an adaptive transformation away from fossil fuels, excess resource extraction, gross inequality, unnecessary wars, waste production, and creating toxic landscapes and show our descendants what humanity humankind is capable of or do just hope that the overwhelming evidence is somehow wrong or that some divine intervention is on the way?" Yes. And while you're up...I'd like a pony...;) Certainly what you say is correct but--and I'll reference you back to your earlier statement that small actions are essentially meaningless--nothing of your utopian agenda can, or will, come to pass until a couple things occur; know that this is coming from a man who has spent his life as optimistic about life and our chances as anyone could possibly be. Till he grew up and figured out human nature, that is. 1) There are too many humans, chasing too few resources, and occupying too small of a "spaceship" for the ship to trimtab its direction in a meaningful--fast, in your vernacular--rapid way. Nature, or us, *will* thin the herd, and until that is done, I see no way we'll attain the level of resource use you assert is needed. To turn a Churchillian phrase around, leave it to mankind to do all the wrong things, right up to the point it does the REALLY wrong thing, and snuffs out a good deal of itself. History is *rife* with such examples and, frankly, I see no turning that around this time, either. That said... 2) We--each and every one of of us who has some voice--has to, read again MUST exert pressure on the leaders to follow the people. None of what you wish to happen; "Leave the car in garage, stop flying, turn the thermostat down, wear more clothes, stop consuming, have a gift free Christmas (share friendship not gifts for everyone's sake?), eat locally and seasonally and be creative about it, to let this be the fun it can be," will or can be done in the vacuum of lax leadership. There are also, oh, I'd say at a guess, about 3 billion souls who do not even come CLOSE to thinking what you posit is, or will be "fun:" I sure don't. Needed? Likely. Easy to attain? Not on your life. Can we? Sandy got a few folks' attention--most notably those who were devastated by the storm's intensity--and even though we cannot say with a high degree Sandy was *caused* by AGW, we do have a pretty good idea that storms like her will become the new normal; when they do, more people will be affected drastically, and at ~that moment~, folks--singular, at-large, and unelected--will really push the pollies to help them do something that is needed. I go back to a position I've long espoused and is typified by the "100th monkey" meme (yes, I know it's been disproved as bunk, but it's as useful an allusion as the equally-debunked "ostrich" meme) and that is, every single person must do whatever little--or much--as they can do, to start that ball rolling. Finally, do you have a source for the assertions you've made, re: the toxicity of solar panels as they age? That's new to me. Even if true, I seriously doubt it's as bad an effect as what burning gigatons of coal does, and has done, to the commons of the atmosphere. we cannot wait for perfect safety.
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    Moderator Response: [DB] Corrected spelling by request.
  16. Ranyl. Yes, yes, yes. But, like any group of addicts - whether addicted to nicotine, ethanol, other carbohydrates, triglycerides, opiates, adrenaline, caffeine, or any of the other pernicious drugs of dependence - breaking free is difficult, and never observed en masse. Policy makers in the carbon emissions context could do worse than to ackowledge the summary made a few years back by Doug Sellman. DOI: 10.1111/j.1360-0443.2009.02673.x
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    Moderator Response: [DB] Hot-linked referenced paper.
  17. "For example PV panels are a toxic waste within 20-30 years, releases tri-nitrofloride to make (a very potent GHG), " hmm, I thought TNF was only used in manufacture of thin-film solar panels, and only very small quantities were emitted. Most PV around today is not thin-film, and if these somehow turn into toxic waste, I would like a reference please. I am also not aware of any rare chemicals in standard solar cells, and they can be made from lower grade silicon.
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  18. Recycling isn’t that easy it seems and is full of chemical and energy intensive processes, just like making the original panels was, so many things not accounted for. Doesn’t really bust any myths but does resort to comparison to nuclear and coal albeit without actual comparison and doesn’t say solar panels aren’t an environmental hazard just says that the risks are minimized in the production process although waste disposal and issues aren’t really addressed that well. Company sponsored paper so will be biased to a degree.
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  19. Vroomie, I agree coal is very likely to be worse than PV's but then I never said use coal as an alternative. All suggest is to consider the issues, consider the carbon cost per potential KWh without displacement savings, remember there is no carbon budget and decide what to spend whatever amount of additional carbon emissions you're prepared to risk on generating energy. The carbon budget is a debt already. So will the addiction to power per se blow the budget in trying to keep the lights on? Almost definately it would appear at present. However the way the weather's shaping up there will be a point of realisation that this is real. Then what? Well who knows lets just hope the budget isn't blown already as the Arctic melt is already very alarming. And fun was inappropriate your right, but it can be creative challenge with parto f that challenge making the lives of the 3 billion in hunger better for them, by accepting migration? Eating less so they can eat more? Stopping wasting food? Laernign how to synergise farming with high productivity into eco-systems such that biodiversity florishes. I always think well even if no else does anything at least I tried to do what I could. BTW the silicon used for solar PV is refiend silicon metal with is 99.9% and highly refiend in high energy intensive toxic substance using processes. Would you work in the factory? Look at the Chinese paper listed in the previous post from Standford, looks pretty industrialised to me.
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  20. "I agree coal is very likely to be worse than PV's but then I never said use coal as an alternative." Since the heart of any rational discussion is an exceedingly-fine understanding of the words and concepts contained therein, let it be clear: *I* never suggested coal as an alternative; I intended that PV be a alternative to coal, as far as it can be, which ain't too far, as of now. Clear now? Your own statement, "I always think well even if no else does anything at least I tried to do what I could.", perfectly illustrates why no one should impugn every individual's ability to impact their local situation--regardless of how "small" the effort would be--in whatever way they can. Edmund Burke said it better, but we all do what we can do, and that cascade of action will eventuate into larger and larger actions. The largest action any of us can make--at least in terms of getting the powers-that-be off their dead asse--is us lighting the fires underneath them. Environmentally benign fires, mind you....;)
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  21. Ranyl, a quick look through various items on your list all apply to thin-film - a rather specialty area in PV. Some of the information is dated as well. In the energy use concerns, what matter is energy yield (amount produced over lifetime cf to energy required to manufacture). For, say northern Europe, with a 20 year lifetime (by which time polycrystalline cells will have dropped to 80% output cf new), this could be as low as 4 (way less than wind), but still very much better than 1. Ratios are much better for say Australia, for CSP, and for new single-pass silicon processes.
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  22. This article suggest thin well on the rise 1500% from above. And the articles age spread was deliberate to shpow that things have been to be toxic for ages and still are. And what si said dosn;t jsut apply to thin that is just tri-ntiroforide and as you well know any silicon used to pureifed to >99% pure. And the maximum efficiency on practice is 12-15%. But hey beleive what you like abotu them, we still have any carbon to spend oon then when other options are much better, like not using so much power.
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  23. The link doesnt take me to that article, but 1500% increase on a very small no. is still a small no. Thin film can mean CdTe with the toxicity problems but can also mean CIGS or psDye technologies. You seem to be claiming nitroflouride is used for other types of PV for which I can find no support at all. It is not used for purification, only for etching. The "big" increase in atmospheric levels (to 0.5 parts per trillion) is more to do with liquid crystal displays than thin film PV. You dont need to spend carbon to make them either. I would also agree that for industrial scale, CSP is better solar option than PV. While I do agree that nothing is cheaper than conservation, making substantial savings in a democracy is difficult to do. I highly recommend Sustainable energy without Hot Air for that kind of study.
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  24. Here’s some geo-engineering that we might be able to all agree on: Fly tankers and fire planes over areas of the permafrost where the surface temperature is below freezing but there is no snow. Equip the planes with snow making equipment. Even a very light dusting of snow will increase the albedo and prevent any further melting by solar radiation. Satellite observations can instruct the pilots where to fly. We have to DO something, don’t we?
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  25. Catman, I fear that the emissions from the planes would do more harm than any good the snow might do. Better just to put sulphur in jet fuel and make the stratosphere more reflective. Not that I'm advocating that either. We have to give an emissions diet a good go before we try the climate equivalent of gastric bypass or liposuction.
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