Modeling Long-Term Permafrost Degradation

Abstract

Permafrost, as an important part of the Cryosphere, has been strongly affected by climate warming, and a wide spread of permafrost responses to the warming is currently observed. In particular, at some locations rather slow rates of permafrost degradations are noticed. We related this behavior to the presence of unfrozen water in frozen fine-grained earth material. In this paper, we examine not-very-commonly-discussed heat flux from the ground surface into the permafrost and consequently discuss implications of the presence of unfrozen liquid water on long-term thawing of permafrost. We conducted a series of numerical experiments and demonstrated that the presence of fine-grained material with substantial unfrozen liquid water content at below 0°C temperature can significantly slow down the thawing rate and hence can increase resilience of permafrost to the warming events. This effect is highly nonlinear, and a difference between the rates of thawing in fine- and coarse-grained materials is more drastic for lower values of heat flux incoming into permafrost. For high heat flux, the difference between these rates almost disappears. As near-surface permafrost temperature increases towards 0°C and the changes in the ground temperature become less evident, the future observation networks should try to incorporate measurements of unfrozen liquid water content in the near-surface permafrost and heat flux into permafrost in addition to the existing temperature observations.