The Transition Zone of Upper Permafrost: The Frontline for Permafrost Changes across Climate and Landscape Gradients

Permanently frozen soils, or permafrost, often contain large amounts of ground ice, which make it vulnerable to climate change and human activities. These soils are protected from melting by a surface layer which thaws in summer and refreezes in winter, and a near-surface layer, termed the transition zone. This transition zone, which develops through complex interactions between the environment and permafrost, controls permafrost resilience to ground surface subsidence (thermokarst). Expectations are that as the climate warms, deeper seasonal melting will impact this transition zone, and ecosystems and infrastructure (i.e., roads, airfields, and buildings) stability. The goals of this project are to evaluate the properties of the transition zone from the High Arctic to the southern border of the permafrost region and to understand processes of formation, degradation, and recovery of the transition zone in various climatic regions. The knowledge gained from this work will inform Arctic science and engineering. The project will support student training. The investigators will collaborate with government agencies and engineering companies whose work is impacted by permafrost ground subsidence issues.

In previous research, the investigators identified a zone in the upper profile of permafrost soils that is critical to permafrost stability, soil development, and geomorphic processes. However, how the thickness and cryostructures of this transition zone (TZ) vary across climate and landscape gradients, the rates of its formation during ecological succession, and how it contributes to permafrost vulnerability and resilience, is not well understood. What knowledge we have is in low Arctic tundra and can be misleading if applied to other bioclimatic regions. To address this gap in knowledge, our collaborative research with the University of Montreal will focus on the TZ across climatic regions and landscapes distributed along a north-south transect from barren polar deserts with continuous permafrost in Canada, to boreal forests in southern Alaska with sporadic permafrost. Our group will also monitor and experiment with mass and heat transfer processes between the active layer (AL) and the TZ to identify mechanisms controlling segregated ice formation.