Climate-driven permafrost thaw releases greenhouse gases (CO₂ and CH₄). Fully frozen permafrost has extremely low gas permeability, acting as a seal that limits gas migration while low temperatureas also inhibit gas generation. Permeability changes during thawrefreeze cycles, however, remain very poorly understood because of the sparsity of experimental data. We report laboratory measurements of gas fraction and gas permeability during thawing of 16 synthetic permafrost samples with a range of initial ice fractions from 5.2% to 62%, for samples considered either fully frozen or fully thawed, as well as a subset of 11 samples with a range of initial ice fractions from 19.3% to 51.2% for which it was possible to make measurements as a function of temperature during thawing. The data show clearly that gas permeability increases during thawing by up to 2.5 orders of magnitude, depending on the initial ice fraction, with the main thawing occurring between -5±0.5°C and -1±0.8°C. The gas permeability uncertainty is in the range ±20% to ±30% for the samples that remained intact. Gas fraction showed similar variation to permeability increasing from 2.62% to 6.16% for fully frozen samples to between 3.16% to 12.51% for fully thawed samples, which is consistent with the ice-water density difference and initial ice fractions. The uncertainty in gas fraction measurements is in the range ±8% to ±12%. These findings confirm that thawing compromises the gas-sealing function of permafrost and provides data to improve large-scale permafrost models. Importantly, they also show that the increase in gas permeability only appears to be the result of increasing gas fraction, with no implied rearrangement of the gas fraction into preferred flow pathways.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)