Support the Arctic Sea Ice Forum and Blog

Author Topic: Arctic Methane Release  (Read 157858 times)

Gray-Wolf

  • ASIF Middle Class
  • Posts: 603
    • View Profile
Re: Arctic Methane Release
« Reply #500 on: November 11, 2017, 02:51:00 PM »
https://watchers.news/2017/10/28/shallow-m6-0-earthquake-hits-north-of-franz-josef-land-arctic-ocean/

Will these quakes cause any issues for the methane reserves on the continental slopes around Svalbard?
KOYAANISQATSI

ko.yaa.nis.katsi (from the Hopi language), n. 1. crazy life. 2. life in turmoil. 3. life disintegrating. 4. life out of balance. 5. a state of life that calls for another way of living.
 
VIRESCIT VULNERE VIRTUS

A-Team

  • ASIF Upper Class
  • Posts: 1966
    • View Profile
Re: Arctic Methane Release
« Reply #501 on: November 13, 2017, 06:01:31 AM »
My reading of S&S is that they see the over-pressurized free methane gas, never mind the hydrates, as by far the greater problem that faces us.
That's correct, Terry. Semiletov estimates the methane hydrates as less than 5% of total ESAS methane; because of this, Shakhova can say the decay timeline of the hydrate stability zone is completely irrelevant because there's already enough free methane gas to catastrophically affect global climate, should even a fraction of it reach the atmosphere.

In view of this, why do people keep bringing up off-site clathrate studies that have zero relevance to ESAS methane release over a 0-20 year time frame?

According to S&S, there do not exist any published studies to date showing ESAS methane hydrates even occurs, whereas we're real sure that methane is currently being released in volume. That methane, from triple isotope studies, is a waste product of archaeal decomposition of buried organic matter. It is not geothermal methane nor destabilized clathrate.

It would be more interesting to chase down the observational basis for S&S's estimate of pressurized free methane volume reserves. Is there really as much down there as they say? How is it distributed relative to the coastline, riverine sediment inputs, and shelf break? Would it really matter if the estimate were 50% too high (or too low)?

And how much pressure has built up under the (deteriorating) permafrost lid and what is its connectivity? That greatly affects the fraction of escaping methane that can reach the atmosphere because slow occasional bubbles have a very different fate -- dissolving into seawater -- from vigorously fountaining methane.

I'm not sure why people keeping throwing in off-ESAS studies of sulfate oxidizing bacteria breaking down the methane before it even leaves the sediment. Obviously that isn't happening to a sufficient extent here. The methane may be rising too rapidly or the sulfate supply was just not there or has been exhausted.

Along the ESAS shelf break, SWERUS core traverses showed MnO and FeO, rather than sulfate, were serving as the terminal oxidants. Landslides there won't matter since the methane is already exhausted.

The ESAS, especially the near-coastal regions rich in methanogenic sediment, is exceedingly shallow, much of it less than 10 m deep. Again, it's baffling why people keep referring to deep sea methane studies or inconsequential shelf areas like the Beaufort with very different histories. Sure, those bubbles will get swept aside by currents and dissolve in sea water, eventually getting metabolized before Henry's Law kicks in.

That isn't the case for over-pressurized methane in shallow water because high volume hotspot vents physically entrain seawater, bringing the methane rapidly near and to the surface where it can equilibrate with (ie raise) the currently low partial pressure of atmospheric methane.

In the interview, Shakhova says "a fraction" will inevitably reach the atmosphere, not specifying that fraction other than to say given the immense estimated methane reserves, its pressure, the erosion of permafrost lid, and beyond-linear rate of hotspot development, that this fraction is all that it would take to seriously disrupt global climate.

S&S have laid out plausible concerns based on decades of observational data. How events will actually play out in the near future depends on the numbers. For those, far more sonar surveys are needed, both of vent activity and subsurface structural changes. The ESAS is so vast and the season so short that it's time-consuming to sample its area with line surveys, much less repeat them to establish a time series.

However -- and this is the whole point of the 2017 NatComm paper -- they have been able to conduct repeat transects and repeat drill cores to a limited extent. Those don't indicate the worst case scenario (a massive one-time blowout) but support decadal-scale accelerating emissions that come close enough in effects.

It won't work to simply monitor atmospheric methane increase (though that's the final arbiter) because it's a lagging indicator for deterioration of the ESAS permafrost lid. As such, it wouldn't give enough time to 'make room' whereas better data might (see #482).
« Last Edit: November 13, 2017, 06:09:17 AM by A-Team »

gerontocrat

  • ASIF Middle Class
  • Posts: 793
    • View Profile
Re: Arctic Methane Release
« Reply #502 on: November 13, 2017, 01:02:11 PM »
My reading of S&S is that they see the over-pressurized free methane gas, never mind the hydrates, as by far the greater problem that faces us.
That's correct, Terry. Semiletov estimates the methane hydrates as less than 5% of total ESAS methane; because of this, Shakhova can say the decay timeline of the hydrate stability zone is completely irrelevant because there's already enough free methane gas to catastrophically affect global climate, should even a fraction of it reach the atmosphere.

...far more sonar surveys are needed, both of vent activity and subsurface structural changes. The ESAS is so vast and the season so short that it's time-consuming to sample its area with line surveys, much less repeat them to establish a time series.


Who will fund the necessary multi-year surveys?
The Russians? Perhaps, due to their determination to exploit the fossil fuel reservoirs of the Arctic they might feel that this is a problem to be ignored?
Will the IPCC highlight this "known unknown" in the next round of reports (or will it be politically unacceptable due to Russian political objections - "get out of MY backyard" - and/or having to accept they missed it last time)  ?

ps:- Even if emissions are slow enough to allow decomposition in the water column, my understanding is this will be through aerobic decomposition by bacteria producing CO2 (acidification) and oxygen depletion possibly on a sufficient scale to result in wide-scale dead zones in the ocean and destruction of marine life. Any evidence anywhere?
"Para a Causa do Povo a Luta Continua!"

Avalonian

  • ASIF Lurker
  • Posts: 49
    • View Profile
Re: Arctic Methane Release
« Reply #503 on: November 13, 2017, 02:14:58 PM »

ps:- Even if emissions are slow enough to allow decomposition in the water column, my understanding is this will be through aerobic decomposition by bacteria producing CO2 (acidification) and oxygen depletion possibly on a sufficient scale to result in wide-scale dead zones in the ocean and destruction of marine life. Any evidence anywhere?

That's basically what happens when productivity in an area is suddenly increased: increased draw-down of carbon, followed by benthic oxygen depletion. Added to that is a slow-down in thermohaline circulation due to the global temperature rise, which just makes any potential worse, and this is why the warmest periods of the Phanerozoic (e.g. Middle Ordovician and Cretaceous) are characterised by a lot of black mudstones with no benthic fossils.

My PhD was on the effects of volcanic ash-fall on Ordovician ecosystems, where the nutrient supply was from upwelling due to hyperpicnal surface waters laden with fine ash, which promptly sank on mass. (The same thing was seen after Pinatubo - a Steve Sparks paper, iirc). The result there was a mass bloom of plankton, followed by benthos, followed by a swift return to anoxia, and, as it happens, lots of exceptional fossil preservation through rapid replacement by pyrite (iron sulphide). And this was only dealing with a local scale, with lateral mixing ameliorating the effects significantly. This process is one of many reasons why CO2 capture by ocean fertilisation was such a spectacularly catastrophic idea; luckily the fish-farming element failed, so it seems to have been largely dropped.

Apologies for lack of reference - I'm currently in a small town in southern China, on fieldwork, and a long way from the literature I was using at the time!

AbruptSLR

  • ASIF Emperor
  • Posts: 13516
    • View Profile
Re: Arctic Methane Release
« Reply #504 on: November 13, 2017, 07:31:37 PM »
As this thread is entitled: "Arctic Methane Release", I provide the following linked 2008 reference.

Kieran D. O'Hara (25 January 2008), "A model for late Quaternary methane ice core signals: Wetlands versus a shallow marine source", Geophysical Research Letters, DOI: 10.1029/2007GL032317

http://onlinelibrary.wiley.com/doi/10.1029/2007GL032317/abstract;jsessionid=2A39482FA5ADB8E882067169E1F82526.f04t01

Abstract: "A three-reservoir model with first order kinetics for methane records in the Vostok (Antarctica) and GISP2 (Greenland) ice cores reproduces the sawtooth pattern and the maximum and minimum concentrations. The model also returns an atmospheric methane relaxation time of ∼10 years for both cores, which is the same as current estimates. The characteristics of the source reservoirs are long relaxation times (33.3 and 100 ky) and high initial methane concentrations (2500 and 7000 ppm) for GISP2 and Vostok, respectively. These characteristics are consistent with gas hydrate sources in shallow marine sediments, but not with wetland sources which have insufficient storage capacity and low source strength."

Also, see the associated 2008 article entitled: "Possible Origin of Methane in Ice Core Records"; which concludes that the methane in both Antarctic and Greenland ice cores for the Late Quaternary period (0.5-1.0 million years ago) is likely associated with methane emitted from marine hydrates

https://www.sciencedaily.com/releases/2008/02/080217093816.htm

The Storegga submarine landslide (see the first attached image) demonstrates that if an abrupt collapse of the WAIS were to trigger Clathrate Gun-type submarine landslides in the Arctic Ocean Basin, then the associate methane release would happen much too quickly for methane-eating microbes to have any meaningful impact on the amount of methane released (as may have been the case for the Late Quaternary Vostok ice core, which the second image indicates includes the Holsteinian, MIS 11c, period; which had a particularly high effective climate sensitivity):

https://phys.org/news/2017-07-methane-eating-microbes-gases-antarctic-ice.html

Extract: "These tiny microorganisms may have a big impact on a warming world by preventing methane from seeping into the atmosphere when ice sheets melt, said Brent Christner, a University of Florida microbiologist and co-author on the study."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

A-Team

  • ASIF Upper Class
  • Posts: 1966
    • View Profile
Re: Arctic Methane Release
« Reply #505 on: November 16, 2017, 03:19:54 PM »
The graphic below (which expands upon a click) summarizes the effects of glaciation in the Arctic Ocean basin. It shows the most recently discovered glacial trough, the De Long, along with many others, summarizing work over many years by M Jakobsson and co-workers.

These troughs cut across the edge of the continental shelf and deposit sediment fans in the deep. The ESAS (resp. Beringia at low sea stand) is quite unusual in that its continental shelf edge was little affected by glaciers during the Pleistocene (because it received insufficient snowfall).

Since sediment fans provide an important organic substrates for archaeal methanogens, little methane is expected along the ESAS which largely lacks them and, while landslides could occur, there is no risk of a 'clathrate gun' for the ESAS. The real risk comes from vast near-shore deposits of free methane gas sitting under a deteriorating permafrost cap, as documented by Semiletov and Shakhova.

"... abundant CH4, including gas hydrates, do not characterize the East Siberian Sea slope or rise along the investigated depth transects. This contradicts previous modeling and discussions, which due to the lack of data are almost entirely based on assumption... metal oxide reduction appears to be the dominant geochemical environment affecting shallow sediment; there is no evidence for upward diffusing CH4. These results strongly suggest that gas hydrates do not occur on any of our depth transect [cores] spread across the continental slope in this region of the Arctic Ocean. This directly conflicts with ideas in multiple publications" Ouch!

https://www.biogeosciences.net/14/2929/2017/bg-14-2929-2017.pdf CM Miller et al 2017

Note the MacKenzie River is surprisingly not associated with a major trough or fan; the main feature in the CAA passes just east of Banks Island. Likewise, Petermann Glacier is not a dominant feature; it appears to have been block by a much larger glacier passing south through the Nares Strait.

These troughs today play an important role in oceanic circulation (ie mixing of incoming warm Atlantic Waters), notably in the Barents Sea and east of Svalbard.

https://www.clim-past.net/13/1269/2017/cp-13-1269-2017.pdf
« Last Edit: November 16, 2017, 06:12:21 PM by A-Team »

AbruptSLR

  • ASIF Emperor
  • Posts: 13516
    • View Profile
Re: Arctic Methane Release
« Reply #506 on: November 20, 2017, 08:39:27 PM »
The graphic below (which expands upon a click) summarizes the effects of glaciation in the Arctic Ocean basin. It shows the most recently discovered glacial trough, the De Long, along with many others, summarizing work over many years by M Jakobsson and co-workers.

These troughs cut across the edge of the continental shelf and deposit sediment fans in the deep. The ESAS (resp. Beringia at low sea stand) is quite unusual in that its continental shelf edge was little affected by glaciers during the Pleistocene (because it received insufficient snowfall).

Since sediment fans provide an important organic substrates for archaeal methanogens, little methane is expected along the ESAS which largely lacks them and, while landslides could occur, there is no risk of a 'clathrate gun' for the ESAS. The real risk comes from vast near-shore deposits of free methane gas sitting under a deteriorating permafrost cap, as documented by Semiletov and Shakhova.

While it is certainly good news that most of the continental shelf edge of the ESAS is not at risk of experiencing 'clathrate gun'-type mechanisms, and while I certainly concur that the near-shore free methane gas sitting under a deteriorating permafrost cap in the ESAS is the most important risk; nevertheless, the graphs in the Miller et al (2017) reference seem to indicate that up to about 50% of the continental shelf edges around the Arctic Ocean basin may be susceptible to a Storegga submarine landslide type methane release.  This is particularly of concern to me as the following Kandiano et al. (2017) reference confirms that during the MIS 11 event freshening of the North Atlantic (due to ice mass loss from the GIS) drove relatively warm intermediate ocean water into the Arctic Basin, and this same mechanism may reoccur in the coming decades.

Kandiano et al. (2017), "Response of the North Atlantic surface and intermediate ocean structure to climate warming of MIS 11" Scientific Reports 7, Article No. 46192, doi:10.1038/srep46192

http://www.nature.com/articles/srep46192

Extract: "Our results underscore the intricate interdynamic behavior of the North Atlantic climate system.  Furthermore, if the present-day rapid summer melting of the GIS continues, the resulting freshening of the surface ocean may well lead to fundamental structural changes in both ocean and atmospheric circulation as reconstructed for MIS 11."

Edit: Also, as cited in Reply #499, Cronin et al. (2017) provides both physical and model evidence that during MIS 11, warm intermediate water flowed from the Atlantic into the Arctic Ocean Basin.  Further, I note that the 12-month running average GMSTA per GISTEMP LOTI thru October 2017 was 1.159C above pre-industrial, which is near the MIS 11 peak.

Cronin et al (2017), "Enhanced Arctic Amplification Began at the Mid-Brunhes Event ~400,000 years ago", Scientific Reports 7, Article No. 14475, doi: 10.1038/s41598-017-13821-2

https://www.nature.com/articles/s41598-017-13821-2

Extract: "Enhanced Arctic amplification at the MBE suggests a major climate threshold was reached at ~400 ka involving Atlantic Meridional Overturning Circulation (AMOC), inflowing warm Atlantic Layer water, ice sheet, sea-ice and ice-shelf feedbacks, and sensitivity to higher post-MBE interglacial CO₂ concentrations."

Edit 2: For those not familiar with how close we are to the MIS 11 peak, I provide the attached image that also indicates where we may well be going to if we continue following a BAU pathway.  Also, I note that the 12-month running GISTEMP LOTI average thru October 2017, above pre-industrial, is currently +1.159C.

Edit 3: The second image shows a close-up of Friedrich et al (2016) projection for GMSTA thru 2100 using paleo-based estimates of ECS vs CMIP5 values.
« Last Edit: November 20, 2017, 11:10:45 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

A-Team

  • ASIF Upper Class
  • Posts: 1966
    • View Profile
Re: Arctic Methane Release
« Reply #507 on: November 22, 2017, 12:47:38 PM »
graphs in Miller 2017 indicate about 50% of the continental shelf edges around the Arctic Ocean basin may be susceptible to a Storegga submarine landslide type methane release. the Kandiano 2017 states that  ice mass loss from the GIS during the MIS 11 event freshened the North Atlantic, drove relatively warm intermediate ocean water into the Arctic Basin.
If you mean Fig.1 in CM Miller 2017, that refers to earlier data-free speculative models that the paper later rejects as totally erroneous at least for the long expanse of the ESAS edge, based on Swerus cores. There is no discussion of landslide susceptibility in this paper and no mention of Storegga, which might have but did not release sufficient methane at sufficiently rapid rates to significantly affect the atmosphere or warm the climate:

Storegga, while unquestionably an enormous marine landslide with a massive follow-up tsunami, has been accurately re-dated in two recent papers to the chilliest decades of the 8.2 ka cold event at 8120–8175 years before AD 1950. Hence its timing is completely off, in terms of the GISP2 methane records and hypothetical methane-induced warming. The JE Begat 2007 paper is thus completely wrong. Landslide-triggered clathrates guns may have occurred in the past but Storegga is not an instance of one.

Because sediment exposed at the base of the slide contained less methane hydrate 8200 years ago than exists today and because Greenland ice cores do not show an increase in methane at the time of the slide, the slide did not release significant volumes of methane to the atmosphere and did not contribute to any change in temperature during or after the 8.2 ka cold event.

The pore water sulphate analysis of Storegga Slide sediments provides a compelling case that the slide could not have released huge quantities of methane gas-hydrates sufficient to leave a detectable signature in the Greenland ice core methane concentration record.  A Dawson 2011 DOI: 10.1177/0959683611400467  See also S Bondevik 2012 doi10.1016/j.quascirev.2012.04.020
 
...pore water sulfate gradient measurements that are used as a proxy for the relative amounts of methane that exist in continental margin sediments associated with the colossal Storegga Slide. These measurements suggest that a considerable inventory of methane occurs in sediments adjacent to, and unaffected by, the Storegga Slide events, but indicate that methane is notably absent from sediments on the sole of the slide and distal deposits created by the slide events.

Either methane was lost during previous Pleistocene failure events or was never present in significant concentrations within the sediments that failed.

http://onlinelibrary.wiley.com/doi/10.1029/2006GL028331/full DK Paull 2017
For the Arctic Ocean perimeter we need to distinguish (1) landslides ongoing for 2.5 myr along the Arctic Ocean continental shelf edge, (2) from significant shelf-edge clathrate abundance/absence, (3) from warm Atlantic and North Pacific mixed incursions already ongoing for decades, (4) from possible large landslides perhaps triggering hypothetically massive and conceivably rapid releases of climate-affecting methane, (5) from real, worsening, non-speculative release of vast shallow ESAS methane gas reaching the atmosphere today.

As observed in the Swerus cores, the ESAS/Laptev margins lacks both clathrate and free methane gas because of ample MnO and FeO are available to methanotrophs (not to mention lower-down S04-2 anaerobic oxidation of methane). Only a small region by the New Siberian Islands has landslide topography. This is already 85% the Siberian shelf perimeter that has zero risk from landslide methane.

The Kara Sea has only near-coastal submerged permafrost and has too shallow a gradient for gravity-driven landslides, so it too is zero risk, regardless of its potential for methane release by other mechanisms. Like the crater-pockmarked Barents, loss of a massive Pleistocene ice sheet greatly reduced pressure needed to sustain clathrates below.

In the Alaskan Beaufort, since submerged permafrost does not extend beyond the 20 m isobath, any earlier free methane gas and clathrate nearer the shelf break was unroofed long ago. Thus the continuing history of mass wastage on outer slopes there poses no risk. Ongoing methane seeps nearer the coast coming from submerged Beringial permafrost might better be considered part of a Greater ESAS.

https://soundwaves.usgs.gov/2017/04/research.html  assumptions proven wrong off Alaska
http://onlinelibrary.wiley.com/doi/10.1029/2012GL052222/full

The CAA has an exceedingly meagre continental shelf that hasn't been accessible to study because of persistent thick ice. Looking at its bathymetry shows a steady incidence of small landslides, occasional sediment fans and only a tiny portion north of Banks Island submerged tundra permafrost. Since MnO and FeO terminal electron acceptors are ubiquitous in the basin, these observations add up to a very minimal risk of climate-affecting methane release along the CAA.

So we seem to be talking about landslide risk along the Svalbard-Severnaya Zemlya arc unless the Fram edge of the Barents Sea is considered part of the Arctic Ocean. While the former was long covered by a thick ice sheet, the latter constitutes barely a percent of the overall shelf perimeter.

The much-studied Vestnesa Ridge there has both thermogenic seeps and clathrate methane, stores that may have been depleted by earlier documented landslides. It could well have more induced in the future as it is the first to see currents of warming Atlantic Water.

However Vestnesa's location is not at all representative of Arctic Ocean continental shelf exposure to warming currents. It seems improbable that such a small area is capable of an abrupt climate-affecting methane release.

https://www.clim-past.net/11/669/2015/cp-11-669-2015.pdf prior Vestnesa methane releases

Thus if massive methane is not there to begin with along long reaches of the Arctic Ocean shelf edge, warmer ocean waters circulating decades from now will not raise the incidence of landslides, much less trigger climate-altering rapid releases of greenhouse gases.

The collapse of the Storegga story undercuts its extension to the Arctic Ocean, as do specifics of the shelf edge there. The risk level is remote, right in there with another Chicxulub or deadly virus escaping from frozen mammoths.

Meanwhile, substantial methane released in the Greater ESAS on a decadal time scale is real and worsening. Effects will be augmented by greenhouse gas emissions from land permafrost, loss of sea ice albedo and various ensuing runaway feedbacks.

By 2030, these three fallouts from Arctic Amplification will likely render null and void assumptions used in current climate model scenarios. We'll have to start all over with a new initial state. And it won't be modeling so much as coping with rapidly oncoming developments.

AbruptSLR

  • ASIF Emperor
  • Posts: 13516
    • View Profile
Re: Arctic Methane Release
« Reply #508 on: November 22, 2017, 07:29:08 PM »
If you mean Fig.1 in CM Miller 2017, that refers to earlier data-free speculative models that the paper later rejects as totally erroneous at least for the long expanse of the ESAS edge, based on Swerus cores. There is no discussion of landslide susceptibility in this paper and no mention of Storegga, which might have but did not release sufficient methane at sufficiently rapid rates to significantly affect the atmosphere or warm the climate:

It is not my intension to be argumentative, but the 2012 article entitled: "Locked greenhouse gas in Arctic sea may be 'climate canary'"; Nature, doi:10.1038/nature.2012.11988; discusses methane hydrates observed in the Canadian Beaufort Seafloor in as little as 290m of water depth, and I imagine that there are many other locations around the Arctic Basin that are comparable to that shown in the attached image:

http://www.nature.com/news/locked-greenhouse-gas-in-arctic-sea-may-be-climate-canary-1.11988

Furthermore, it is not my intension to suggest that the 'clathrate gun' mechanism needs to be the main source of past, or future, methane emissions from the Arctic, nor that one major submarine slide such as Storegga needs to fully account for atmospheric methane concentrations during the 8.2 kya event.  With continued warming there are likely to be multiple activated sources of natural methane emissions including shallow water sources from the ESAS, thermokarst lakes, tropical peatlands, etc.; and all work synergistally to increase the lifetime of methane in the atmosphere by competing for hydroxyl ions.  Thus I believe that possible methane emissions from multiple submarine landslides scattered around the Arctic Ocean Basin (but possibly not in the ESAS) should be more closely evaluated by climate scientists as one more possible positive feedback mechanism to include in their ESMs.
« Last Edit: November 23, 2017, 01:44:58 AM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Shared Humanity

  • ASIF Upper Class
  • Posts: 2329
    • View Profile
Re: Arctic Methane Release
« Reply #509 on: November 23, 2017, 01:16:27 AM »
If you mean Fig.1 in CM Miller 2017, that refers to earlier data-free speculative models that the paper later rejects as totally erroneous at least for the long expanse of the ESAS edge, based on Swerus cores. There is no discussion of landslide susceptibility in this paper and no mention of Storegga, which might have but did not release sufficient methane at sufficiently rapid rates to significantly affect the atmosphere or warm the climate:

It is not my intension to be argumentative,

Please, not to worry. I can't imagine anything more I'd rather witness than 2 ASIF heavy weights going toe to toe in the ring. I'm going to get me a ring side seat.

AbruptSLR

  • ASIF Emperor
  • Posts: 13516
    • View Profile
Re: Arctic Methane Release
« Reply #510 on: November 23, 2017, 02:20:37 AM »
My main point is that while it is relatively easy to dismiss one individual positive feedback mechanism at a time, when one properly evaluates the synergy between all Arctic methane emission sources together, they can results in significant Arctic Amplification with time.  Both of the linked articles note that the clathrate gun hypothesis merits more research, in the context of a larger picture of possible future impacts from atmospheric methane (of which the clathrate gun contribution may only be one of many different future sources of methane emissions), particularly if we move towards PETM-like conditions (as mentioned in the second article by Gavin Schmidt):

Title: "Early warnings of an out-of-control climate"

https://phys.org/news/2017-04-early-out-of-control-climate.html

Extract: ""The great concern is the rapid rise, over the last three years, in methane levels in the atmosphere. Methane is a gas with 28 times the planet-heating power of carbon dioxide. Scientists estimate there may be as much as 5 trillion tonnes of it locked in permafrost and seabed deposits.

"There is mounting evidence that, as the planet warms due to human activity, these vast reserves of greenhouse gas are now starting to melt and vent naturally. The Earth's past history shows this could unleash runaway global warming, driving up planetary temperatures by as much as 9 or 10 degrees Celsius.

"At such temperatures, some scientists consider there is a high risk the planet would become uninhabitable to humans and large animals," Mr Cribb says."

See also:
Surviving the 21st Century: Humanity's Ten Great Challenges and How We Can Overcome Them. www.springer.com/us/book/9783319412696

&

The second linked article is authored by Gavin Schmidt.

Title: "Methane: A Scientific Journey from Obscurity to Climate Super-Stardom"

https://www.giss.nasa.gov/research/features/200409_methane/

Extract: "Most importantly, clathrates can be explosively unstable if the temperature increases or the pressure decreases — which can happen as a function of climate change, tectonic uplift or undersea landslides.

The importance of these clathrates in climate change has only recently started to be appreciated. The first clue was some puzzling data from a period 55 million years ago. In the early 1990's, Jim Kennett of Scripps Institute of Oceanography and his colleagues noticed that during an extremely short amount of time (geologically speaking) at the transition between the Paleocene and Eocene epochs, carbon isotope ratios everywhere (the deep sea, on land, at the poles and in the tropics) suddenly changed to favour the lighter 12C isotope of carbon at the expense of 13C. The rapidity and size of this change was unprecedented in the period since the demise of the dinosaurs, and this excursion was simultaneous with a short period of extreme global warming (around 3 to 4 degrees globally, more in the high latitudes).

In 1995, Jerry Dickens of Rice University suggested that the only conceivable perturbation to the global carbon cycle to fit these data was a massive input of light carbon that had been stored as methane clathrates, which are observed to be particularly high in 12C. Nothing else could be as fast-acting or have enough of the lighter isotope to have had the observed effects. Given that both CH4 and its oxidization product CO2 are greenhouse gases, this might explain the global warming as well.

Subsequent work, including atmospheric chemistry studies by myself and Drew Shindell of NASA GISS, have confirmed that this hypothesis is still the most likely candidate, although the initial triggering mechanism is unknown. Similar ideas have been proposed to explain short term events in the Jurassic, at the Permian-Triassic boundary and in the Neo-Proterozoic, although the evidence for a unique role of methane in these cases is much weaker than at the Paleocene/Eocene boundary.

With a plausible role for methane clathrates in the Paleocene, it is only natural to examine whether they played a similar role in more recent climate changes, such as rapid climate variability during the last ice age. There are some tantalizing clues. In ocean sediments offshore of California, Kai-Uwe Hinrichs and colleagues at Woods Hole recently found geochemical traces of clathrate releases coincident with warmings in the Greenland ice core records. In some records, there are coincident spikes in the carbon isotope record, reminiscent of the Paleocene/Eocene spike but of lower amplitude. This has led Jim Kennett to propose the so-called "clathrate gun hypothesis", that methane builds up in clathrates during cold periods, and as a warming starts it is explosively released, leading to enhanced further rapid climate warming. This idea is not yet widely accepted, mainly because the records of methane in the ice cores seems to lag the temperature changes, and the magnitudes involved do not appear large enough to significantly perturb the radiative balance of the planet. The more conventional explanation is that as the climate warms there is increased rain in the tropics and thus increased emissions from tropical wetlands which need to have been large enough to counteract a probable increase in the methane sink. There is, however, much that we don't understand about the methane cycle during the ice ages, and maybe hydrates will eventually be considered part of the rapid climate change story."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 13516
    • View Profile
Re: Arctic Methane Release
« Reply #511 on: November 23, 2017, 02:35:33 AM »
Who knows whether we are headed towards PETM-like conditions anytime soon, but the linked article provides evidence from calcite that emissions from methane hydrates made a significant contribution to that event, and includes this statement:

"The rapidity of the methane hydrate emission lasting from several years to thousands of years was tempered by the equally rapid oxidation of the atmospheric and oceanic methane that gradually reduced its warming potential but not before global warming had reached levels lethal to most life on land and in the oceans."

Brand et al. (2016), "Methane Hydrate: Killer cause of Earth's greatest mass extinction", Palaeoworld, https://doi.org/10.1016/j.palwor.2016.06.002

http://www.sciencedirect.com/science/article/pii/S1871174X16300488

Abstract: "The cause for the end Permian mass extinction, the greatest challenge life on Earth faced in its geologic history, is still hotly debated by scientists. The most significant marker of this event is the negative δ13C shift and rebound recorded in marine carbonates with a duration ranging from 2000 to 19 000 years depending on localities and sedimentation rates. Leading causes for the event are Siberian trap volcanism and the emission of greenhouse gases with consequent global warming. Measurements of gases vaulted in calcite of end Permian brachiopods and whole rock document significant differences in normal atmospheric equilibrium concentration in gases between modern and end Permian seawaters. The gas composition of the end Permian brachiopod-inclusions reflects dramatically higher seawater carbon dioxide and methane contents leading up to the biotic event. Initial global warming of 8–11 °C sourced by isotopically light carbon dioxide from volcanic emissions triggered the release of isotopically lighter methane from permafrost and shelf sediment methane hydrates. Consequently, the huge quantities of methane emitted into the atmosphere and the oceans accelerated global warming and marked the negative δ13C spike observed in marine carbonates, documenting the onset of the mass extinction period. The rapidity of the methane hydrate emission lasting from several years to thousands of years was tempered by the equally rapid oxidation of the atmospheric and oceanic methane that gradually reduced its warming potential but not before global warming had reached levels lethal to most life on land and in the oceans. Based on measurements of gases trapped in biogenic and abiogenic calcite, the release of methane (of ∼3–14% of total C stored) from permafrost and shelf sediment methane hydrate is deemed the ultimate source and cause for the dramatic life-changing global warming (GMAT > 34 °C) and oceanic negative-carbon isotope excursion observed at the end Permian. Global warming triggered by the massive release of carbon dioxide may be catastrophic, but the release of methane from hydrate may be apocalyptic. The end Permian holds an important lesson for humanity regarding the issue it faces today with greenhouse gas emissions, global warming, and climate change."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

wili

  • ASIF Upper Class
  • Posts: 2072
    • View Profile
Re: Arctic Methane Release
« Reply #512 on: November 23, 2017, 03:44:01 AM »
Thanks for that piece, ASLR, as always. When you say "PETM-like" do you mean "PTME-like"?

I think the first usually refers to the Paleocene-Eocene Thermal Maximum about 55 mya, which was really bad. But the near total wipe out that you seem to be referring to is End Permian, or Permian-Triassic Mass Extinction (or Great Dying...), right? I must confess getting those acronyms messed up myself quite often, though, so I may be getting confused here myself.
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

AbruptSLR

  • ASIF Emperor
  • Posts: 13516
    • View Profile
Re: Arctic Methane Release
« Reply #513 on: November 23, 2017, 11:49:02 AM »
wili,

As noted in the Wikipedia article below, both the PETM and the PTME are good examples of the current clathrate-gun hypothesis, where massive releases of methane occur as a result of an initial triggering abrupt climate change event (not as the triggering event itself).  Thus, when I wrote PETM-like I was referring to the Paleocene–Eocene Thermal Maximum 56 million years ago, as the first attached image shows that without considering either the collapse of the WAIS or a clathrate-gun event we could be at 5 to 6C GMSTA by 2100 (based on ECS calibrated to the paleorecord over the past 800,000 years).  However, per the second attached image Hansen et al (2016) indicates that the collapse of the WAIS (which Bakker et al 2017 indicates might happen during the 2040-2090 timeframe, see the third image) could increase the planetary energy imbalance by over 2 Watts/sq meter in a pulse.  While, the collapse of the WAIS leads to a cooling of the surface temperatures over the Southern Ocean, due to the bipolar seesaw mechanism it would result in a marked increase in Arctic Amplification (see the fourth image from Wolfe et al 2017, with data from the Middle Eocene, and I note that our current CO2e is over 530ppm which is comparable to that during the Middle Eocene); which in turn might trigger a clathrate gun event, maybe as early as 2100.

Title: "Clathrate gun hypothesis"

https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis
&
https://courses.seas.harvard.edu/climate/eli/Courses/global-change-debates/Sources/Methane-Clathrate-gun-hypothesis/1-Clathrate%20gun%20hypothesis-Wikipedia.pdf

Extract: "… there is stronger evidence that runaway methane clathrate breakdown may have caused drastic alteration of the ocean environment (such as ocean acidification and ocean stratification) and of the atmosphere of earth on a number of occasions in the past, over timescales of tens of thousands of years. These events include the Paleocene–Eocene Thermal Maximum 56 million years ago, and most notably the Permian–Triassic extinction event, when up to 96% of all marine species became extinct, 252 million years ago."

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 13516
    • View Profile
Re: Arctic Methane Release
« Reply #514 on: November 23, 2017, 12:04:15 PM »
Just to reiterate my point that we are currently at an atmospheric CO2e of over 530ppm, which is not too different from Eocene conditions, I provide the following reference & associated image.  Under such conditions the Hadley Cell could expand to the Arctic before 2100:

Jagniecki,Elliot A. et al. (2015), "Eocene atmospheric CO2from the nahcolite proxy", Geology, http://dx.doi.org/10.1130/G36886.1


http://geology.gsapubs.org/content/early/2015/10/23/G36886.1

ftp://rock.geosociety.org/pub/reposit/2015/2015357.pdf

Abstract: "Estimates of the atmospheric concentration of CO2, [CO2]atm, for the "hothouse" climate of the early Eocene climatic optimum (EECO) vary for different proxies. Extensive beds of the mineral nahcolite (NaHCO3) in evaporite deposits of the Green River Formation, Piceance Creek Basin, Colorado, USA, previously established [CO2]atm for the EECO to be >1125 ppm by volume (ppm). Here, we present experimental data that revise the sodium carbonate mineral equilibria as a function of [CO2] and temperature. Co-precipitation of nahcolite and halite (NaCl) now establishes a well-constrained lower [CO2]atm limit of 680 ppm for the EECO. Paleotemperature estimates from leaf fossils and fluid inclusions in halite suggest an upper limit for [CO2]atm in the EECO from the nahcolite proxy of ∼1260 ppm. These data support a causal connection between elevated [CO2]atm and early Eocene global warmth, but at significantly lower [CO2]atm than previously thought, which suggests that ancient climates on Earth may have been more sensitive to a doubling of [CO2]atm than is currently assumed."

Extract: "These results show that [CO₂]atm may not have been as high as previously thought during the warmest interval of the Cenozoic, implying a climate sensitivity for CO₂ that is roughly twice as high as is currently assumed (Royer et al., 2012)."

See also:
https://www.sciencenews.org/article/eocene-temperature-spike-caused-half-much-co2-once-thought

Extract: "During the Eocene around 50 million years ago, climbing CO2 levels heated the planet by more than 5 degrees Celsius. By examining crystals grown in this “hothouse” climate, researchers discovered that Eocene CO2 levels were as low as 680 parts per million. That’s nearly half the 1,125 ppm predicted by previous, less accurate crystal experiments, the researchers report online October 23 in Geology."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

wili

  • ASIF Upper Class
  • Posts: 2072
    • View Profile
Re: Arctic Methane Release
« Reply #515 on: November 23, 2017, 03:48:23 PM »
Ah, thanks for the clarification, and, as always for the great links and graphs!
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

sidd

  • ASIF Upper Class
  • Posts: 1817
    • View Profile
Re: Arctic Methane Release
« Reply #516 on: November 24, 2017, 09:29:28 AM »
Some time ago I had the privilege to have dinner with some from Byrd center at Ohio State. I recall discussing the clathrate methane issue. I was left with the impression that methane release from seabed was less troubling than release from wet decomposition of siberian peatlands as ice lenses melted.

sidd

TerryM

  • ASIF Upper Class
  • Posts: 2352
    • View Profile
Re: Arctic Methane Release
« Reply #517 on: November 24, 2017, 01:36:35 PM »
Storegga, while unquestionably an enormous marine landslide with a massive follow-up tsunami, has been accurately re-dated in two recent papers to the chilliest decades of the 8.2 ka cold event at 8120–8175 years before AD 1950. Hence its timing is completely off, in terms of the GISP2 methane records and hypothetical methane-induced warming. The JE Begat 2007 paper is thus completely wrong.
As I understand it clathrates require both low temperatures and high pressure. During a rapid chill the Warm Atlantic Waters wouldn't be affected, but Sea Level would have dropped.


If the clathrate's temperature remained constant, but the pressure was reduced, even slightly, this would lead to the sudden destruction of any clathrate delicately balanced between stability and destruction.


If ASLR takes place prior to much warming of the clathrate itself, I'd expect the clathrate to remain stable, because of the additional pressure.


Terry

AbruptSLR

  • ASIF Emperor
  • Posts: 13516
    • View Profile
Re: Arctic Methane Release
« Reply #518 on: November 24, 2017, 04:42:12 PM »
Some time ago I had the privilege to have dinner with some from Byrd center at Ohio State. I recall discussing the clathrate methane issue. I was left with the impression that methane release from seabed was less troubling than release from wet decomposition of siberian peatlands as ice lenses melted.

sidd

sidd,

The first image shows a computer projection of methane emissions from thermokarst lakes (which form from the melted ice lenses particularly in the Siberian peatlands) in the Arctic, which shows the risk of large spike of methane emissions circa 2050 if we continue on a RCP 8.5 until that time.  Thus, I (very much) concur with the concerns of the Byrd Center scientists.

However, the issue that I keep raising, is that while it is efficient for scientists to work productively in their respective silos of expertise and to identify risks from individual feedback mechanisms; science demands that these individual mechanisms be brought together synergistically in the best ESMs available before we can understand what our truth risks are.  This is why I keep pointing-out that our current ESMs are not fully dynamical and they pick and choose what to focuses on and what to leave out of their models (such as hosing events).

Thus while I believe that methane emissions from hydrate decomposition will have a rather limited effect on climate change before say 2090; I still believe that it is valuable to include this mechanism with state-of-the-art ESMs because if we continued to follow SSP5 baseline (RCP 8.5) to 2050 and if ECS is currently say 4.5C, then the WAIS collapse would be unstoppable (even if we stop following SSP5 baseline then), which would likely trigger at least a 2 Watt/sq m pulse of planetary energy imbalance (for a few decades), which could trigger an abrupt expansion of the Hadley Cell in the NH if this trigger point is as low as an atmospheric CO2e concentration of about 680ppm (see my last post) caused by a short-term pulse of methane (say from thermokarst lakes and/or shallow ESAS methane sources).  Once triggered (say circa 2090), the second attached image shows that an expanded NH Hadley Cell would remain stable even after the short-term pulse had ended.  This is a brief explanation of why ESM projections past say 2090 should be capable of trying to model a clathrate-gun mechanism as they currently are incapable of matching the paleo-record of numerous Super Interglacial events.

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 13516
    • View Profile
Re: Arctic Methane Release
« Reply #519 on: November 24, 2017, 05:32:30 PM »
Storegga, while unquestionably an enormous marine landslide with a massive follow-up tsunami, has been accurately re-dated in two recent papers to the chilliest decades of the 8.2 ka cold event at 8120–8175 years before AD 1950. Hence its timing is completely off, in terms of the GISP2 methane records and hypothetical methane-induced warming. The JE Begat 2007 paper is thus completely wrong.
As I understand it clathrates require both low temperatures and high pressure. During a rapid chill the Warm Atlantic Waters wouldn't be affected, but Sea Level would have dropped.


If the clathrate's temperature remained constant, but the pressure was reduced, even slightly, this would lead to the sudden destruction of any clathrate delicately balanced between stability and destruction.


If ASLR takes place prior to much warming of the clathrate itself, I'd expect the clathrate to remain stable, because of the additional pressure.


Terry

Terry,

Climate change is complex (to say the least), and while it is true that increasing pressure (say due to increasing sea level) helps to stabilize methane hydrates (see the first attached temperature-pressure phase diagram for methane hydrates from the linked Wikipedia article), which would have helped to limit methane emissions from hydrate decomposition during the last interglacial (MIS 5); this does not necessarily mean that we are all safe from a "… sudden release of natural gas from methane clathrate deposits in runaway climate change …" by the end of this century.

First, as noted in the extract below hydrates exhibit a metastable state at lower temperatures rather than by higher pressures (than indicated by the phase diagram); which may have contributed to relatedly low methane emissions from Arctic methane hydrate decomposition during MIS 5; but this metastable state could be abruptly over-come with the additions of small amounts of heat (say due higher Arctic Amplification than MIS 5 experienced, after 2090 if the WAIS collapses).

Second, it takes time for heat to migrate through mass (e.g. soil and ice) thus the fact that the Arctic during the Holocene has already had over 10,000 years for heat to migrate through the seafloor of submerged continental shelves, means that you can't just point at MIS 5 and say that the sub-seafloor thermal profiles are currently the same as that when MIS 5 approached its peak (see the second image)

Third, as I mentioned to sidd in my last post, current ESM models can't replicate the response of Super Interglacials, and thus they cannot say whether some synergistic combination of potential feedback mechanism (as methane emissions from thermokarst lakes, WAIS collapse, NH Hadley Cell expansion to the Arctic, etc) may trigger a runaway climate change situation driven by methane from hydrates after say 2100, even if humans stop GHG emissions all together.

Title: "Clathrate gun hypothesis"

https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis

Extract: "The sudden release of large amounts of natural gas from methane clathrate deposits in runaway climate change could be a cause of past, future, and present climate changes. The release of this trapped methane is a potential major outcome of a rise in temperature; some have suggested that this was a main factor in the planet warming 6 °C, which happened during the end-Permian extinction, as methane is much more powerful as a greenhouse gas than carbon dioxide. Despite its atmospheric lifetime of around 12 years, it has a global warming potential of 72 over 20 years, 25 over 100 years, and 33 when accounted for aerosol interactions. The theory also predicts this will greatly affect available oxygen and hydroxyl radical content of the atmosphere.

Another kind of exception is in clathrates associated with the Arctic ocean, where clathrates can exist in shallower water stabilized by lower temperatures rather than higher pressures; these may potentially be marginally stable much closer to the surface of the sea-bed, stabilized by a frozen 'lid' of permafrost preventing methane escape.

The so-called self-preservation phenomenon has been intensively studied by Russian geologists starting in the late 1980s. This metastable clathrate state can be a basis for release events of methane excursions, such as during the interval of the last glacial maximum. A study from 2010 concluded with the possibility for a trigger of abrupt climate warming based on metastable methane clathrates in the East Siberian Arctic Shelf (ESAS) region."

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Cid_Yama

  • ASIF Citizen
  • Posts: 135
    • View Profile
    • The Post Peak Oil Historian
Re: Arctic Methane Release
« Reply #520 on: November 30, 2017, 08:09:35 AM »
I would like to leave a link to my methane archive as I have been following this for over a decade.

Hopefully it will prove useful.

Metastable Hydrate can exist within the permafrost, which preserves it, well above the HSZ.  This appears to be responsible for the blowouts from the pingo-like formations.

One litre of fully saturated methane hydrate solid contains about 120 grams of methane (or around 169 litres of methane gas at 0°C and 1 atm).

When hydrates dissociate, the volume released is 169X that of the hydrate, creating pore pressure within the sediment that can literally blowout the above sediment like a champagne cork.

Hydrates don't melt.  They dissociate instantaneously when the phase transition is reached.

When an area of hydrates dissociates and releases, causing a blowout, it can relieve pressure on neighboring hydrates, which can lead to a chain reaction of release over a larger area.

If no blowout, it adds to the pressure within the sediments, seeking pathways of release.     

Sea level rise will be insufficient to preserve the hydrates.

The pressure at depth on the Siberian Shelf is around 1 Megapascal. The temperature of the hydrates per Semilitov in 2008 was at 272 Kelvins.

As can be seen by the chart, we would need to raise sea level 200 meters to restore stability pressure wise. Obviously, we can rule that out. Since the only other option would be to lower temperatures more than 20 K(also not possible), it's all over.

A-Team is correct in that the immediate danger isn't the hydrates, but the free gas within the sediments just looking for a way to escape.  But the metastable hydrates can be a threat multiplier.

After all, a blowout provides a pathway for escape.     
     

« Last Edit: November 30, 2017, 10:09:18 AM by Cid_Yama »

Cid_Yama

  • ASIF Citizen
  • Posts: 135
    • View Profile
    • The Post Peak Oil Historian
Re: Arctic Methane Release
« Reply #521 on: November 30, 2017, 09:56:06 AM »
AbruptSLR, you may find this informative.

Warming the Fuel for the Fire: thermal dissociation of methane hydrate during the PETM
Dramatic warming and upheaval of the carbon system at the end of the Paleocene Epoch have been linked to massive dissociation of sedimentary methane hydrate. We present new highresolution stable isotope records based on analyses of single planktonic and benthic foraminiferal shells from Ocean Drilling Program Site 690 (Weddell Sea, Southern Ocean), demonstrating that the initial carbon isotope excursion was geologically instantaneous and was preceded by a brief period of gradual surface water warming. Both of these findings support the thermal dissociation of methane hydrate as the cause of the PETM carbon isotope excursion. Furthermore, the data reveal that the methane-derived carbon was slowly mixed from the surface ocean downward, suggesting that a significant fraction of the initial dissociated hydrate methane reached the atmosphere prior to oxidation.

The stratigraphic progression of single-specimen stable isotope changes, with the decrease in surface water δ18O values preceding the decrease in δ13C values, enables us to rule out several possible explanations of PETM carbon input. The onset of the CIE would have preceded the decrease in δ18O values if the PETM had resulted from erosion-induced hydrate dissociation (e.g., Katz et al., 2001) or from a carbonaceous impactor (e.g., Kent et al., 2001). Explosive volcanism (e.g., Bralower et al., 1997) would have resulted in an increase or no change in δ18O values at a high-latitude site. Thus, the only plausible mechanism to consider is the thermal dissociation of methane hydrates. The occurrence of specimens of surface-dwelling foraminifera that record transitional δ18O values and pre-CIE δ13C values (Level 1, Figure 3) suggests a ~2°C warming of surface waters prior to the onset of the CIE.

The top-down progression of the onset of the CIE suggests that a significant proportion of the methane from dissociated hydrates was rapidly transferred to the atmosphere and surface ocean. In order for calcifying organisms to record a methane-derived δ13C anomaly, the isotopically light methane must first be oxidized into CO2 and incorporated into the HCO3 - pool from which calcification occurs. Because the pattern of CIE propagation proceeded downward from surface waters, oxidation of methane must have taken place within the atmosphere/surface ocean. Had the initial release of methane been more gradual (enabling oxidation within the deep ocean), Site 690 planktonic foraminifera would have recorded transitional δ13C values at the onset of the event, and benthic individuals would have recorded the excursion prior to the planktonics.

We note that the top-down progression in carbon input observed at the PETM is strikingly similar to the recent changes in the atmospheric and surface ocean carbon reservoirs in response to release of anthropogenic CO2.

We propose the following scenario to explain the stratigraphic sequence of events in the new stable isotope data. Gradual warming occurred first in surface waters, then in waters at thermocline and intermediate depths. Subduction or downwelling of warmer intermediate waters in the region of water mass formation led to thermal dissociation of methane hydrates at a location with a significant sedimentary hydrate content. Methane gas from the dissociated hydrates reached the atmosphere prior to widespread oxidation.
link

Release of free methane reservoirs in recently submerged relic permafrost sediments would also account for it.  Since such free gas reservoirs would be comprised of gas from previously dissociated hydrates, it would look the same.

As it is now believed that the methane was releases in 3 pulses,  the step-wise deepening of the HSZ would account for that. 
« Last Edit: November 30, 2017, 10:05:45 AM by Cid_Yama »

Cid_Yama

  • ASIF Citizen
  • Posts: 135
    • View Profile
    • The Post Peak Oil Historian
Re: Arctic Methane Release
« Reply #522 on: November 30, 2017, 10:17:48 AM »
And this Paper claims that the initial PETM CIE occurred over a 13 year period.

Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum

It is now recognized that methane excursions were involved in the Permian-Triassic, Triassic-Jurassic, and several other more minor extinction events, suggesting that this is not a rare event, but a repeating geological process.

   
« Last Edit: November 30, 2017, 10:31:17 AM by Cid_Yama »

A-Team

  • ASIF Upper Class
  • Posts: 1966
    • View Profile
Re: Arctic Methane Release
« Reply #523 on: November 30, 2017, 11:09:07 AM »
And this [2002 PNAS] Paper claims that the initial PETM CIE occurred over a 13 year period.
It appears that they got it wrong, or at least didn't persuade too many people in the field. When the data was reviewed in 2017, other scientists came up with <5,000 years as best estimate for PETM onset. The second 2017 paper, using boron isotopes, attributes the whole episode to volcanism:

https://en.wikipedia.org/wiki/North_Atlantic_Igneous_Province
http://www.geus.dk/departments/geol-mapping/projects/n-atlantic-ign-provin-uk.htm

In summary, there is currently no justification for attributing the PETM to methane clathrate release and, along with the collapse of the Storegga clathrate story, no established paleo precedent for climate impacts from this mechanism (though it is still an attractive one).

A probabilistic assessment of the rapidity of PETM onset
SK Turner et al
Nature Communications  2017
https://www.nature.com/articles/s41467-017-00292-2 open access

Knowledge of the onset duration of the Paleocene-Eocene Thermal Maximum—the largest known greenhouse-gas-driven global warming event of the Cenozoic—is central to drawing inferences for future climate change. Single-foraminifera measurements of the associated carbon isotope excursion from Maud Rise (South Atlantic Ocean) are controversial, as they seem to indicate geologically instantaneous carbon release and anomalously long ocean mixing.

Here, we fundamentally reinterpret this record and extract the likely PETM onset duration. First, we employ an Earth system model to illustrate how the response of ocean circulation to warming does not support the interpretation of instantaneous carbon release. Instead, we use a novel sediment-mixing model to show how changes in the relative population sizes of calcareous plankton, combined with sediment mixing, can explain the observations.

Furthermore, for any plausible PETM onset duration and sampling methodology, we place a probability on not sampling an intermediate, syn-excursion isotopic value. Assuming mixed-layer carbonate production continued at Maud Rise, we deduce the PETM onset was likely <5 kyr.

During the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma), the rapid injection of isotopically depleted carbon to the atmosphere (and/or ocean) was imprinted in the geological record as a prominent negative carbon isotope excursion. Associated with this is evidence for a ~5 °C global temperature rise, ocean acidification, and a variety of global biotic changes in marine and terrestrial archives.

The PETM is thus widely recognized as the best known analog to date for future greenhouse-gas-driven global warming. However, the timescale of the event is critical to the value of inferences that can be drawn regarding future climate change and ecosystem response—particularly with respect to the duration of main carbon release (PETM onset), which we define as the interval between pre-PETM carbon isotope values and the recorded carbon isotope minimum.

Existing estimates for the duration of PETM onset range from near instantaneous (refs 7,8,9) to tens of kyr (ref 10), with the lower-end estimates proving particularly contentious (ref 11,12,13,14).

Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum
Marcus Gutjahr et al
https://www.nature.com/articles/nature23646 paywalled

The PETM was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates. However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming.

Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data—a proxy for seawater pH—that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event.

We find strong evidence for a much larger (more than 10,000 petagrams)—and, on average, isotopically heavier—carbon source than considered previously. This leads us to identify volcanism associated with the North Atlantic Igneous Province, rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event.
« Last Edit: November 30, 2017, 11:55:31 AM by A-Team »

AbruptSLR

  • ASIF Emperor
  • Posts: 13516
    • View Profile
Re: Arctic Methane Release
« Reply #524 on: December 01, 2017, 05:08:07 PM »
I find the evidence compelling that the a clathrate gun mechanism likely not occur during the PETM (in any significant way); however, the same cannot be said for the Permian–Triassic extinction event, when up to 96% of all marine species became extinct, 252 million years ago (see the linked reference); nor does this mean that isolated submarine landsides might emit relatively small (but not insignificant) amounts of methane from hydrates into the atmosphere this century (with sufficient continued warming):

Brand et al. (2016), "Methane Hydrate: Killer cause of Earth's greatest mass extinction", Palaeoworld, Volume 25, Issue 4, Pages 496-507, https://doi.org/10.1016/j.palwor.2016.06.002

http://www.sciencedirect.com/science/article/pii/S1871174X16300488

Abstract: "The cause for the end Permian mass extinction, the greatest challenge life on Earth faced in its geologic history, is still hotly debated by scientists. The most significant marker of this event is the negative δ13C shift and rebound recorded in marine carbonates with a duration ranging from 2000 to 19 000 years depending on localities and sedimentation rates. Leading causes for the event are Siberian trap volcanism and the emission of greenhouse gases with consequent global warming. Measurements of gases vaulted in calcite of end Permian brachiopods and whole rock document significant differences in normal atmospheric equilibrium concentration in gases between modern and end Permian seawaters. The gas composition of the end Permian brachiopod-inclusions reflects dramatically higher seawater carbon dioxide and methane contents leading up to the biotic event. Initial global warming of 8–11 °C sourced by isotopically light carbon dioxide from volcanic emissions triggered the release of isotopically lighter methane from permafrost and shelf sediment methane hydrates. Consequently, the huge quantities of methane emitted into the atmosphere and the oceans accelerated global warming and marked the negative δ13C spike observed in marine carbonates, documenting the onset of the mass extinction period. The rapidity of the methane hydrate emission lasting from several years to thousands of years was tempered by the equally rapid oxidation of the atmospheric and oceanic methane that gradually reduced its warming potential but not before global warming had reached levels lethal to most life on land and in the oceans. Based on measurements of gases trapped in biogenic and abiogenic calcite, the release of methane (of ∼3–14% of total C stored) from permafrost and shelf sediment methane hydrate is deemed the ultimate source and cause for the dramatic life-changing global warming (GMAT > 34 °C) and oceanic negative-carbon isotope excursion observed at the end Permian. Global warming triggered by the massive release of carbon dioxide may be catastrophic, but the release of methane from hydrate may be apocalyptic. The end Permian holds an important lesson for humanity regarding the issue it faces today with greenhouse gas emissions, global warming, and climate change."

See also:

http://www.independent.co.uk/environment/earth-permian-mass-extinction-apocalypse-warning-climate-change-frozen-methane-a7648006.html
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 13516
    • View Profile
Re: Arctic Methane Release
« Reply #525 on: December 05, 2017, 12:18:59 AM »
The attached plot by NOAA shows atmospheric methane concentrations at Barrow, Alaska from 2005 thru Dec 4 2017.  Per the follow extract, the circle symbols are supposed to be representative data while the green + symbols are not supposed to be representative data.  It looks to me that the circle symbols are much higher at this time of year than in years past:

Extract: "Circle Symbols are thought to be regionally representative of a remote, well-mixed troposphere.

+ Symbols are thought to be not indicative of background conditions, and represent poorly mixed air masses influenced by local or regional anthropogenic sources or strong local biospheric sources or sinks."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson