Arctic Methane - This Does Not Sound Good...

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88. Methane Time Bomb in Arctic Seas – Apocalypse Not

http://dotearth.blogs.nytimes.com/2011/12/14/methane-time-bomb-in-arctic-seas-apocalypse-not/

[font face="Times, Serif"]December 14, 2011, 5:43 pm
[font size="5"]Methane Time Bomb in Arctic Seas – Apocalypse Not[/font]
By ANDREW C. REVKIN

A very important research effort has been under way during recent summers in the warming, increasingly ice-free shallows off Russia’s Siberian coast. There, an international array of scientists has been investigating widening areas of open water that are disgorging millions of tons of methane each year.

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If you read the Independent of Britain, you’d certainly be thinking the worst. The newspaper has led the charge in fomenting worry over the gas emissions, with portentous, and remarkably similar, stories in 2008 and this week.

If you read geophysical journals and survey scientists tracking past and future methane emissions, you get an entirely different picture:

A paper published in Dec. 6 in the Journal of Geophysical Research appears to confirm pretty convincingly that the gas emissions seen in recent years are from a thawing process that has been under way for 8,000 years — since seas rose sufficiently to cover the near-shore seabed. Sharp warming of the sea in the region since 1985 has clearly had an influence on the seabed, according to the paper, led by Igor Dmitrenko of the Leibniz Institute of Marine Sciences in Kiel, Germany.

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http://dx.doi.org/10.1029/2011JC007218

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Summer hydrographic data (1920–2009) show a dramatic warming of the bottom water layer over the eastern Siberian shelf coastal zone (<10 m depth), since the mid-1980s, by 2.1°C. We attribute this warming to changes in the Arctic atmosphere. The enhanced summer cyclonicity results in warmer air temperatures and a reduction in ice extent, mainly through thermodynamic melting. This leads to a lengthening of the summer open-water season and to more solar heating of the water column. The permafrost modeling indicates, however, that a significant change in the permafrost depth lags behind the imposed changes in surface temperature, and after 25 years of summer seafloor warming (as observed from 1985 to 2009), the upper boundary of permafrost deepens only by &#8764;1 m. Thus, the observed increase in temperature does not lead to a destabilization of methane-bearing subsea permafrost or to an increase in methane emission. The CH4 supersaturation, recently reported from the eastern Siberian shelf, is believed to be the result of the degradation of subsea permafrost that is due to the long-lasting warming initiated by permafrost submergence about 8000 years ago rather than from those triggered by recent Arctic climate changes. A significant degradation of subsea permafrost is expected to be detectable at the beginning of the next millennium. Until that time, the simulated permafrost table shows a deepening down to &#8764;70 m below the seafloor that is considered to be important for the stability of the subsea permafrost and the permafrost-related gas hydrate stability zone.

[font size="4"]5. Summary and Conclusions[/font]

|32| Summer hydrographic data (1920–2009) show a dramatic warming of the bottom water layer over the eastern Siberian shelf coastal zone (<10 m depth) since the mid-1980s, by 2.1°C. We attribute this warming to changes in the Arctic atmosphere. The enhanced summer cyclonicity results in warmer air temperature and a reduction in ice extent, mainly through thermodynamic melting. This leads to a lengthening of the summer open-water season and to more solar heating of the water column.

|33| The permafrost modeling shows that a significant change in the permafrost depth lags behind the imposed changes in surface temperature. Thus, a significant degradation of subsea permafrost is expected to be detectable only at the beginning of the next millennium. Until that time (the year 3000), the simulated permafrost table shows a deepening down to ~70 m below the seafloor (Figure 5). This depth of the frozen permafrost is still less than that of the GHSZ, but only within errors of the simulated depth of the GHSZ upper boundary. Taking into account the uncertainties in the simulated results and lack of direct observations, this deepening is considered to be important for the stability of the subsea permafrost and the GHSZ.

|34| In summary, our results do not support the hypothesis that the recent CH4 supersaturation, reported by Shakhova et al. |2010|, was triggered by recent Arctic climate changes. Instead, it is more likely the result of the continuous degradation of subsea permafrost associated with the warming initiated by permafrost submergence ~8000 years B.P.. Overall, while our data provide evidence of drastic bottom layer heating over the coastal zone during summer, the increase in temperature could not produce an immediate response in thawing the subsea Arctic permafrost causing the increase in methane emission. In this context, we share a viewpoint of Petrenko et al. |2010| that “a newly discovered CH4 source is not necessarily a changing source, much less a source that is changing in response to Arctic warming.” Marine hydrates are destabilized on timescales of millennia because of the large inertia associated with oceanic circulation and heat propagation in sediments |O'Connor et al., 2010|. Continuing climate change, however, may significantly increase summer seafloor bottom temperatures over the coastal zone, which may have an important impact on the stability of offshore submarine permafrost already in the next millennium.

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