Arctic methane outgassing on the E Siberian Shelf part 2 - an interview with Dr Natalia Shakhova

Posted on  January 2012 by John Mason

In December 2011, following a fresh flurry of sometimes conflicting media reports about methane outgassing on the East Siberia Arctic Shelf (ESAS), we decided to go and talk to the people doing the work on the ground. We are pleased to report that Dr Natalia Shalhova (NS below) of the University of Alaska in Fairbanks agreed to be interviewed by the author, on behalf of Skeptical Science, via email. Here are the responses, verbatim, to our questions.

Above: Bathymetric map (source - NOAA) of the Arctic with key features noted and the subject area highlighted in red.

SkS: In your JGR paper from 2010 you state that methane hydrate in Siberia can occur at depths as shallow as 20 m. Have any such remarkably shallow methane hydrate deposits on the ESAS been directly observed/sampled and if so, how could methane hydrate have formed at such depths?

NS: Yes, such shallow hydrates were sampled in Siberia. They form as a result of the so-called “self-preservation phenomenon” and they are termed “metastable”. This phenomenon has been intensively studied by Russian geologists starting in the late 1980s.

SkS: Your 2011 field season is reported to have located kilometre-diameter plumes of outgassing methane. Are these located in areas visited in previous seasons?

NS: These were new sites from that part of the ESAS that was investigated very sparsely before. In our previous investigations we mainly focused on the shallower part of the ESAS, which composes about 70% of the total area and provides a very short conduit for methane to escape to the atmosphere. Besides, because we worked mostly on small vessels, we were not allowed to navigate far enough from the coasts to reach the mid-outer shelf where water is relatively deep on the scale of the shallow ESAS (>50 m depth). That is why deeper waters were under-represented and were considered a minor contributor to annual emissions. Last summer’s findings made us re-consider our previous constraint on the annual emission budget; they highlight the need to further assess underestimated components of annual fluxes from the ESAS.

Searching for methane in such an extensive area is truly like searching for a needle in a haystack. The ESAS is more than 2 million square kilometers in extent.  Even if we study ~10 000 km2 every year (100x100 km, which is a lot!), it will take >200 years to investigate the entire ESAS! Even then, the probability of finding a hot spot 1 km in diameter within the study area will still be only 0.01%.  

SkS: Have you done any analyses/isotopic studies of the fugitive gas to see if anything can be learned about its provenance (i.e., biogenic, thermogenic, destabilized hydrate or a combination of these)?

NS: Yes, we conducted an isotopic analysis to obtain the isotopic signature of the methane dissolved in the water column. The isotopic signature indicates a mixture of methane of different origins. We are currently making an effort to investigate particular sources.

SkS: Do the observed methane outgassing sites tend to correlate with features seen on acoustic imaging of the sea bed (e.g. taliks, pock marks, fractures) or on deep seismic data (e.g. fault-zones, anticlines and other structures)?

NS: We believe that methane outgassing sites primarily correlate with features like those you list above.  Our data, although they are still limited, clearly exhibit such a correlation. Unfortunately, there are some limitations in usage of both hydro-acoustic and deep seismic methods imposed by the shallowness of the water column and the ubiquity of shallow gas fronts in the sediments.  In addition, our ability to obtain extensive records was constrained by our limited funds; to date we only have ~3000 nautical miles of such recordings.

SkS: A critical question at this point is whether the outgassing is a recent development as a consequence of the dramatic Arctic warming of the past
thirty years, or an ongoing, long-term response to the Holocene inundation of the ESAS. What are your thoughts on this and, on a similar line of
enquiry, would it be possible to determine the age of the organic matter the methane was originally derived from?

NS: An entire second paragraph of our paper published in Science (Shakhova et al., 2010) is devoted to addressing this question! We were the ones who hypothesized - and devoted our entire study to testing this hypothesis - that methane release from the Arctic shelf is determined by the change in thermal regime of permafrost inundated thousands of years ago. I do not understand why this question should arise over and over again or, moreover, be considered critical. As we deal with the long-lasting permafrost warming caused by the warming effect of the overlying seawater, is there any logic in negating the contribution of the recent warming, which caused additional warming of that overlaying sea water?  I believe that there is absolutely no point in trying to determine who is responsible, Mother Nature or human beings. Whoever is responsible, the consequences will be the same. 

As for determining the age of the organic matter the methane was derived from, it is very hard to distinguish between modern and ancient sources. The mean age of organic matter preserved even in the surface sediments in the ESAS is 6-8 thousand years, and when you go deeper, you find older organic matter. “Talik” is a term used to describe an unfrozen layer of ground within a still-frozen permafrost body.  As taliks develop within the sub-sea permafrost, organic matter of different ages could provide the substrate for methanogenesis. This means that modern methane could be produced from organic matter of different ages, and this is also true of pre-formed methane.

SkS: The recent reports of substantial releases of methane on the ESAS prompt us to ask how these observed emissions could detectably change global atmospheric methane concentrations and in what timeframe?

NS: To date, we have only taken the very first steps down the long path of learning enough to answer this question. We officially reported only 8 Tg of methane was being released from the ESAS per year. This reported amount is <2% of the total annual global methane release and would not detectably change global atmospheric methane concentrations. However, we did not incorporate a few emission components – probably the most important ones - because of some uncertainties still remaining concerning their constraints. Newly obtained data, without question, indicate that annual methane emissions from the ESAS have been underestimated. To say how significant the underestimated components are, and to identify the mechanisms responsible for such substantial releases, we need to carefully analyze obtained data and, very likely, conduct further investigations on a broader scale. To be able to answer your question, which is a core question of our study as well, we need to establish at least a few observatory sites to trace dynamic atmospheric concentrations of methane; we need to develop a monitoring net to detect changes occurring in known plume areas; we also need to continue all-season observations in this region to study temporal and spatial variability in methane releases and the factors that determine this variability. We undoubtedly need to learn much more than we currently know. We call for the involvement of serious funding organizations to give this study the level of support that is consistent with the importance of this topic.

SkS: With respect to future events, in your EGU 2008 abstract it is stated that "we consider release of up to 50Gt of predicted amount of hydrate
storage as highly possible for abrupt release at any time". This represents a colossal quantity of gas. How quickly could such a release occur and what would be the most likely mechanism?

NS: I believe that the non-gradual (massive, abrupt) emission mode exists for a variety of reasons. First, wherever in the World Ocean such methane outgassing releases from decaying hydrates occur, they appear to be torch-like with emission rates that change by orders of magnitude within just a few minutes. Note that there was no additional seal such as permafrost to restrict emissions for hundreds of thousands of years anywhere in the World Ocean. Imagine what quantity of methane has been stored beneath sub-sea permafrost if even now, when the permeability of permafrost is still limited, the amount of methane annually escaping from the ESAS is equal to that escaping from the entire World Ocean. Another important factor is that conversion of hydrates to free gas leads to a significant increase in the gas pressure. This highly-pressurized gas exerts a geological power that creates its own gas migration pathways (so-called “chimneys” within sediments). It is even more important to understand that the nature of the permafrost transition from frozen to unfrozen is such that this physical process is not always gradual: the phase transition itself appears to be a relatively short, abrupt transformation, like opening a valve. Remember that the gas “pipeline” is highly pressurized. There could be several different triggers for massive releases: a seismic or tectonic event, endogenous seismicity caused by sediments subsiding pursuant to hydrate decay, or sediment sliding on the shelf break; the shelf slope is very steep, and the sedimentation rates are among the highest in the ESAS. As for the amount that could possibly be released, this estimate represents only a small fraction of the total amount of methane believed to be stored in the ESAS (3.5% of 1400 Gt). Because these emissions occur from extremely shallow water, methane could reach the atmosphere with almost no alteration; the time scale of such releases would largely depend on the spatial distribution and capacity of the gas migration pathways.

SkS: A previous methane release of such a magnitude, occurring abruptly, would logically manifest as a spike in the global methane concentration record, yet the ice-core methane record has no such spikes during previous interglacials. Is there any evidence for massive methane release events
having occurred further back - e.g. at any point during the Cenozoic?

NS: You would better address such a question to a specialist in paleo-climatology. To my knowledge, there are a few episodes in the Earth’s history attributed to abrupt methane releases. Interpretation of ice-core methane records may not be relevant, because these records are too short to reach back to the entire Cenozoic.

Skeptical Science would like to thank Dr Shakhova for her contributions. 

Notes

The "self preservation phenomenon" mentioned by Dr Shakhova in her reply to the first question is well-known in Russian and other northern petrochemical industry circles, where much discussion may be found. It is temperature-dependent i.e. it requires fairly low temperatures to work. For more information, see Self-preservation of gas hydrates (PDF) for a briefing. 

Summary

The research team have located new and large (~1km wide) plumes of outgassing methane, in areas not previously investigated, so this is not necessarily a recent development: at least, there are no previous data from these areas to compare the large plumes with.

That the area has seen warming over a prolonged time since the Holocene transgression and that there has been an additional, sharp recent warming event is well-documented. Whether there is increased outgassing caused by the additional recent warming is an important question that requires urgent investigation, a point indeed made in Shakhova et al's 2010 paper in Science  - PDF - see last paragraph.

Further work will better constrain known current methane emissions to the atmosphere, currently estimated to be 8 Tg (1 Tg=1 million tonnes) per year. Clearly, because new sources have been identified, the figure is greater than 8Tg but how much so remains to be discovered.  

A large (multi-gigaton) abrupt release event is considered possible, but when is not known. It is important to remember that hydrocarbons, including methane, migrate upwards through the Earth's crust from their source-rocks due to their low density. Basic oil geology tells us that recoverable oil and gas deposits occur where such upward migration has been blocked by an impermeable barrier (an oil- or gas-trap) such as a salt-dome or anticline including thick impermeable strata such as a clay-bed. In such places, the accumulation can build up to the point where the oil/gas is in an highly pressurised state - hence the "blowouts" that have been recorded over the years in some oilfields. What Shakhova is suggesting is that if buried gas hydrates destabilise, what could result is accumulations of pressurised methane capped off by permafrost, which because it is degrading might lose its effectiveness as a gas-trap. The same point would, I suggest, apply to non-hydrate derived methane i.e. gas that has remained as gas. What one would likely see in such a scenario would be a strong increase in outgassing, not in one great "burp" at one locality but via multiple pathways up through the defrosted sediment over a wide area.

David Archer, who has worked extensively with gas hydrates, looks at some release scenarios over at Realclimate, here and here.

Some afterthoughts

In February 2002, the then U.S. defence secretary Donald Rumsfeld famously said: "There are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns – there are things we do not know we don't know." He was lambasted and ridiculed for this at the time. However, at face value, all politics aside, the statement has more than a ring of truth to it.

My scientific background is in mineralogy, and I hope I may offer an analogy which illustrates what is meant by "known knowns, known unknowns and unknown unknowns". During the 1980s, I and a number of other mineralogists started to turn up samples of a mineral forming beautiful vivid pale-green spiky crystals. These were found at old metal-mines in Mid-Wales and the English Lake District: first at one locality then another and another. Despite having all the tools of mineral identification at our disposal, including x-ray diffraction and the electron microscope, we could not match it to any known species. Before we started to find specimens, it had lain there in the mine spoil, an unknown unknown, for centuries. Now we had specimens and could study it but not identify it, it was a known unknown. Finally, nearly twenty years after the first discovery, it became a known known - redgillite, named after one of its localities: a basic sulphate of copper with its crystallography and chemistry described in detail in the peer-reviewed journal Mineralogical Magazine.

above: from unknown unknown to known unknown to known known: redgillite, first described in 2004.

I offer this not as an off-topic distraction but as an example of the way in which science proceeds. In almost every case it is the same: only the timescale may vary. Something new is discovered yet is not fully understood. That uncertainty, however, gives pointers towards follow-up work: in time the uncertainties are whittled away one by one and the whole picture becomes clear. It is a journey which will be familiar to anyone working in any of the many branches of academic research. Shakhova and her colleagues have embarked on a journey of challenging proportions: less than a decade ago they discovered what had to that point been an unknown unknown. Now they have described some of the known knowns: we now know without doubt that methane is venting to Earth's atmosphere from parts of the ESAS seabed in copious quantities as a response - a positive feedback - to warming. Furthermore, they have identified many of the known unknowns for follow-up study. They have rightly called for the setting-up of an observational network in the area and they are planning their research for the coming years in a physically and logistically-challenging area.

Outside of science, people seem to work differently a lot of the time, wanting a black-or-white world where everything is a known known. That there are no absolute, cover-all conclusions yet from the ESAS might come as a disappointment to some. However, this is maybe a time to reflect that, 116 years ago, Arrhenius figured out that adding carbon dioxide to the Earth's atmosphere would raise Earth's surface temperature over time. That has been a known known ever since, reinforced by study after study after study, during which time we have raised carbon dioxide levels well beyond anything during the geologically recent glacial-interglacial cycles, so that we are now heading, decade by decade, towards the climate of the mid-Cenozoic,  methane or no methane.

Very interesting responses! I'm not sure what we should add in the way of commentary, except a note of thanks. I'm not sure how it would look if we were to say, for example, that we found some of the responses inadequate. For example:

• I thought the answer to Q1 was a little vague and she could have provided some references and some better explanation of how very shallow hydrates could have formed on the ESAS, if there are any shallow hydrates there at all.
• Also, I thought the answer to Q6 was a little peevish and I am very surprized that she says that the question of attribution of the emissions to short-term human warming or long-term natural warming is unimportant.  ("I believe that there is absolutely no point in trying to determine who is responsible, Mother Nature or human beings".) Since human warming is likely to greatly increase over the decades to come, the consequences of recognizing even a small amount human attribution thus far seem obvious to me. In fact, this point is the very reason that her work is getting so much attention. 

It may be best not to add any comments on the science in the blog post but rather to leave those for the comments section. If Dr Shakhova responds directly or indirectly (ie by email to John) to points raised in the comments, then we could add the comment and response to the end of the blog post as an update.

John, did you clean up her English at all? 

Thanks for doing this!

Added later, further to my point about her confusing answer to question 6, in the 2010 Science article she wrote in the concluding paragraph:

To discern whether this extensive CH4 venting over the ESAS is a steadily ongoing phenomenon or signals the start of a more massive CH4 release period, there is an urgent need for expanded multifaceted investigations into these inaccessible but climate-sensitive shelf seas north of Siberia.

Responses from Dr Shakhova are very interesting with only two surprises for me (1) increasing high gas pressure causing pingo formation and (2) sudden eruption being deemed more likely than sustained build-up of annual venting to dangerous levels. 

I had expected talik formation to increase emission and reduce pressure of sedimentary gas.  While recognising that massive landslide at the shelf edge could expose shallow clathrate, I thought that since no area of potential slippage had been identified, it was unlikely unless associated with major seismic disturbance - which does not seem to have occurred recently.  The chances of the latter occurring are of course possible on the ESAS.  Shakhova and others have frequently reported it as an active seismic area.

Perhaps Q 6 might have been better phrased as an inquiry into the on-going effects of Arctic amplification on future methane releases, rather than looking backwards.  Shakhova has already made it clear in her 2010 Paper that ESAS methane releases have been initiated by flooding of the continental shelf, now exacerbated by ESAS seabed increase of 3°C over last 30 years, surface temperature increase of 5°C causing earlier, more frequent development of polynyas and increased exposure of seawater to sunlight.

What I want to know – you too? – is what are the anticipated effects of on-going Arctic warming likely to be on erosion of a once impermeable permafrost cap on: i. growing annual release of CH4, ii. lowering pressure of sedimentary gas and iii. destabilising shallow clathrate deposits due to warming of sediments/loss of gas pressure?

Shakhovas’ views on these aspects might indicate the likelihood of CH4 venting build-up in coming years.  As previously pointed out, off-shore CH4 deposits are much more vulnerable in the immediate shorter term to the effects of Arctic amplification than  on-shore deposits.  Do you suppose these aspects might be addressed as a follow-up question?

Logic suggests to me on-going warming will occur and accelerate permafrost decay promoting formation of migratory gas channels over a wider area, reducing gas pressure on shallow clathrate and raising the temperature of encasing sediment to >0°C.  The result – rapid increase in annual venting of CH4.  But over what time-frame for this scenario to develop to the point that it becomes dangerous?  10 years, a century, or longer?  I doubt longer 

I also note that in her response to Q8, Shakhova quantifies CH4 deposits on the ESAS as 1,400 Gtonnes which is significantly lower than earlier ESAS estimates given in her Washington (Dec. 2010) presentation which indicated shallow clathrate (1,000 Gtonnes), sedimentary gas (700 Gtonnes) and permafrost (500 Gtonnes).   Clarification would be useful.

It was suggested that Shakhova might be willing to respond to comments made on Part 2.  Was this put to her as a standing invitation?  Has she agreed 

Are there to be further questions prior to publication of Part-2?  If so, I suggest that a possible follow-up question might be along the lines:

“You have identified ESAS sources of CH₄ as comprising hydrates (1,000 Gtonnes), gas (700 Gtonnes) and permafrost (500 Gtonnes).  In your estimation what is the relative vulnerability of these sources to the effects of on-going global warming in general and Arctic amplification in particular?”

My guess is that sedimentary gas is the likely source of present venting and the most vulnerable due to the effects of AGW but Shakhova may have quite different views and is not very clear on this in her response to Q

Of course, Shakhova may not appear to be forthcoming because she has yet to complete analysis of data available to her, or maybe the data is not yet sufficiently complete, or she does not want to reveal everything yet to be published in pending Papers?

It would also be interesting to know the salt content of the thawed sediments found by S&S at 53 metres beneath the ESAS “seabed” – but that may be revealed in their forthcoming Paper?

Skepticism regarding shallow clathrate deposits is understandable but if Shakhova and other Russian scientists confirm their existence and physical presence, should we not be more concerned about their magnitude and likely destabilisation in a warming world?

I would prefer that you leave out the question numbers (and question 3, and question 10) and put the questions and answers below each other as if it would be a discussion. I don't know how to describe the effect the numbering makes to me (at least in English) but the numbering sort of makes it look mechanic, impersonal, and not very dynamic.

Thanks folks, and yes I think the formatting need not be so formal. Yes the answers are pasted in verbatim from the email I received!

Shakhova has responded to my query about publication: we are good to go with this once I have tidied it up as per fellow SkS-er comments. They are still analysing last years' data and it looks like there will be no "official' annoincement until the summer at the earliest.

The discussion with these two pieces may prove quite lively! I've been giving commentary in the piece itself a lot of thought and I believe it offers an excellent opportunity to demonstrate how scientific uncertainty may be identified and tackled: the story is a classic example of how science works. I have an excellent analogy from my mineralogical background that should engage with all readers :)

Cheers - John

Have added some afterthoughts which hopefully serve to illustrate whereabouts within the scientific process these guys currently are - I hope the analogy works! I have also repeated the call made on Realclimate and elsewhere for people not to take their eye off the ball that is CO2. Perhaps the whats and ifs WRT large methane burps - a known unknown - are best thrashed out in the comments beneath?

Cheers - John

PS - via the rapid response team/Scott Mandia what is now the final question will hopefully be answered in more detail. He tells me there are a couple of folk on the case. Have told Shakhova I'll email her a link when the piece is online and that she and her colleagues would be most welcome to join in the discussion.

Cheers - John

Have added notes concerning the "self preservation phenomenon" with a relevant link, because readers will want to know what that is.

Have written a brief summary concerning the main points, with a link to the 2010 paper and have linked to David Archer's recent pieces over at RC.

Just need the paleoclimatology guys to respond via Scott now!

Cheers - John

John - good summary.  Thanks for your work.

Unfortunately Dr Shakhova's responses raise many more questions than are asked or answered so I do hope she will be willing to participate in the comments which this article is certain to attract.  

Based on what she says, I remain unconvinced about a sudden, abrupt emission of 50+ Gtonnes being more likely than gradual build-up to >3 Gtonnes/annum over the next 50 years or less.

Agnostic - what they have done would have been like me going to the press halfway through my postgrad research! However I can entirely understand why they did this - to attract and challenge academic interest. The potential geohazards of the ESAS most definitely warrant very detailed investigation and there is so much work to do that more than one team are required. I don't think she knows the answers beyond what she has said, such is the magnitude of the task ahead.

When I started work on this last month I have to admit I was losing sleep over the disaster-scenarios. This is no longer the case. I just lose sleep over CO2 emissions as usual instead! Am now discussing the Cenozoic with some paleo-guys for a final short paragraph to slip in.

Cheers - John

In terms of abrupt major emission, or gradual build-up of venting from the seabed of the ESAS - or both! - there is no doubt in my mind that if CO2 is the cake thenb methane is definately the icing on it.  There is equal reason for you to loose sleep over CO2 and CH4.  I loose sleep over neither, knowing that there is little that nation states intend to do about AGW and nothing they can do about slow feedbacks.

Cheers - zzzzz

I've got Part 2 slotted for Wednesday if it's ready by then John.

Cool, Dana! Word of warning - the small images are juxtaposed with text in tables. Holler if I need to get these better sorted! I can dump the tables if that would make things easier for you.

Cheers - John

Actually John, if you could get this ready by putting it into a blog post, that would help a lot.  I'm not sure if the tables will work, but have a go at it.

Will do, Dana. Having looked at Part 1 in the flesh, I have realised the tables are not a good idea. Is there a way of just wrapping text R or L of images in the main editor?

Cheers - John

If you can figure out how to do it in HTML, you can use the HTML editor.  That's probably the way to go.

Thanks Dana. Have put it together now:

arctic-methane-outgassing-e-siberian-shelf-part2

Please note that I have dated it January 18th (Wednesday) - so if you want to publish it on another day you'll be wanting to change the date, too :)

Cheers - John

Dana, this post can go up today (I'm only a pending author so can't publish it myself). Haven't had any response from Zachos yet - maybe he's not around. Can always use that for a post on Cenozoic methane releases in anycase.

Cheers - John

Ooops - the blog editor did something very strange to my hyperlinks!

I have posted all the correct ones in response #2 below the blog. Not sure what happened there as they were perfectly OK in the old version of the piece above! Sorry about that.

Cheers - John

Fixed the links in the OP for you; sometimes the editor goes whack-o on links.

Dan, thanks v. much! Note to self: test all links thoroughly in future!

Cheers - John