Thawing Permafrost Releases Unanticipated Reservoirs of “Fossil” Methane

Proceedings of the National Academy of Sciences, August 10

Two regions of Siberian permafrost seem to be releasing methane that comes from limestone caves or reservoirs, rather than decay of thawed organic material in the permafrost itself. Methane normally is released from permafrost if it thaws under wet conditions, such as from soils under lakes or wetlands (while under drier conditions, thawed permafrost releases carbon dioxide, CO2). In these two regions of the Tamyr Peninsula of Northern Siberia however, such “wet” conditions are not present. Instead, they have large “dry” areas of limestone caves and outcroppings, with frozen carbonate rock formations. These rocky lands have released far greater concentrations of methane than their vegetation-covered surroundings since the summer of 2020, when Northern Siberia experienced an extreme heat wave, with temperatures reaching nearly 6°C above the 1979-2000 average.

Authors hypothesize that the extreme heat wave unclogged fractures and sub-surface caves within or below this “dry” permafrost, rapidly releasing built-up reservoirs of methane into the atmosphere. These reservoirs might be ancient methane – similar to fossil fuel deposits – or may have built up during previous thaw events, but were prevented from release by the overlying rock and soils. Regardless, these new observations hint that very large amounts of methane could be emitted from deep rock reservoirs within and below frozen permafrost, adding onto the methane and CO2 directly emitted by thawing permafrost caused by ongoing human carbon emissions.

https://www.pnas.org/content/118/32/e2107632118