Large plumes of methane bubbling up from the Arctic Ocean sea-bed, saturating the water column, venting into the air, adding significantly more heat forcing to an already dangerous, fossil fuel-based, accumulation of greenhouse gasses in the Earth’s atmosphere. It’s a nightmare scenario. One in which human-forced warming, already at 1 C above 1880s levels, is further amplified through the feedback release of ancient carbon stored over the past 8 million years of Northern Hemisphere glaciation. And a recent study by the now famous Semiletov and Shakhova team provides still more reason for appropriate concern that such an event may be in the works.
(Shakhova and Semiletov’s new study produces an increasingly clear picture of a destabilizing organic carbon store beneath thawing permafrost in the East Siberian Arctic Shelf region. The above images show organic carbon concentration [left frame] and rate of release of methane in grams per square meter per day over observed regions. Image source: The Royal Society.)
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By now, many of us are familiar with the controversy over the potential risks of significant-to-catastrophic methane release due to human-forced warming of the Arctic. An increasing number of observational specialists are pointing toward a risk that rapid human warming will set off the release of still more carbon in the Arctic. For some, this release is expected to be gradual. Others believe there’s enough risk of a rapid release to warrant an equally rapid emergency response.
But regardless of where you stand on the issue, new research coming to light from some of the Arctic’s top observational scientists more clearly describes what appears to be an increasingly dangerous situation.
Disintegrating Permafrost Cap in ESAS
At issue is the fact that, at the end of the last ice age, a great store of permafrost carbon was submerged as the Arctic Ocean rose. A low lying region containing about 500 billion tons of carbon as methane became inundated by the shallow sea that is the East Siberian Arctic Shelf (ESAS). The waters of this sea remained cold — below the freezing point of non-salt water in its lower reaches for most of the year. But, in some places, warmth invaded, and it is thought that small portions of the permafrost cap deteriorated.
In the near shore zones and in geologically active zones, methane conduits called taliks developed. And from these expanding taliks an increasing amount of methane bubbled to the surface.
(Ivashkina Lagoon was once a thermokarst lake. It has since been flooded by the Laptev Sea. For much of the time of inundation, the fresh water lake surface remained frozen. It is now thawing and releasing its organic carbon store as methane. Image source: The Royal Society.)
However, for the most part, the permafrost cap over the methane stores remained in tact — waiting to be rejuvenated by a new ice age. That is, until human industry belched billions of tons of carbon into the atmosphere, removing the possibility of a new ice age and forcing the world ocean and connecting Arctic Ocean to begin to warm in excess of peak Holocene temperatures. This warming, twice as fast in the Arctic as in the rest of the world, added still more heat pressure to the permafrost cap locking methane within the ESAS sea floor.
Now, more and more permafrost beneath the shallow ESAS waters is starting to thaw. And this, much more rapid than normal thaw is resulting in an increasing risk that methane stores beneath the permafrost cap will destabilize.
Shallow Waters, Geothermal Hot Spots, Taliks
Recent observational records by Dr. Natalia Shakhova and Dr. Igor Semiletov have found what they hypothesize to be an expanding array of methane vents in the East Siberian Arctic Shelf sea bed. According to their recent research, the vents appear to be growing more robust — bubbling up greater volumes of methane from a more vigorous and inter-connected network of channel beneath the thawing sea floor.
(Ever since 2005, atmospheric methane levels have again been on the rise. Much of this increase may be due to human emissions. However, an overburden of atmospheric methane and carbon dioxide in the Arctic zone hints that destabilizing carbon stores may also be adding substantial volumes of greenhouse gasses to the world’s airs. Image source: NOAA OSPO.)
Currently, according to Shakhova and Semiletov, methane emissions are most vigorous in the near-shore region of the ESAS and in the offshore slope region. Shakhova and Semiletov believe that near shore emissions are increasingly active due to rapid warming occurring there. Not only are the regional waters impacted by a rapidly warming Siberian land mass. They also see the flux of hotter waters from rivers issuing from the continent. As a result, the near shore region is most vulnerable to permafrost thaw and destabilization. In the slope zone, however, geological features are more active. These features provide a natural heat for the formation of taliks. And though most of this region was once frozen to the point that even geological activity did not result in methane venting, the now warming permafrost cap is generating weaker regions that natural geological heat can exploit to greater and greater degrees.
Sea Ice Melt, Storms, Heighten Methane Emissions
Ever since the mid 2000s Shakhova and Semiletov have observed what appears to be a generally heightened methane emission coming from the ESAS. Estimates for total release rates have doubled and then doubled again. By 2013, the scientists were estimating that 17 million tons of methane was venting from the ESAS sea surface each year.
The increased rate of methane release is not only due to permafrost thaw on the sea floor. It is also due to an increase in large polynyas in the ESAS during winter time as well as an overall increase in the area of open water that can be impacted by storms. An ice locked ESAS keeps more of its methane in the water column and gives the methane a longer period to be absorbed by the water or consumed by microbes. But as the ice recedes, more of the methane is able to break the surface and reach the airs above. In addition, ice free seas are more susceptible to the action of storms. Storms increase wave heights, increase the rate of breaking waves, and reduces ocean surface stratification. As a result methane moves more rapidly through the upper level water column and encounters a larger surface area from which to transfer from water to air.
An ice free ESAS is not only warmer, generating more destabilization forcing to the permafrost cap which locks in methane, it is also more and more devoid of the surface ice cap which acts as a secondary barrier to methane to air transfer.
Shakhova, Semiletov Recommend Adding ESAS Methane Release to Global Climate Models
Shakhova and Semiletov’s findings continue to compel them to issue warnings over the prospect of continuing increases in methane emissions from the ESAS and nearby seas. They conclude:
The observed range in CH4 emissions associated with different degrees of subsea permafrost disintegration implies substantial and potent emission enhancement in the ESAS as the process of subsea permafrost thawing progresses with time. While it is still unclear how quickly CH4 flux rates will change, the current process of Arctic warming and associated sea ice loss will accelerate this process. The potential for the release of substantial amounts of CH4 from the ESAS region has important implications not only for atmospheric CH4 concentrations but also, given CH4‘s potency as a greenhouse gas, for the global climate. Because the ESAS contains the largest and arguably most vulnerable stores of subsea CH4, inclusion of the ESAS source in global climate models should be considered a high priority.