Abstract

Permafrost is a layer of perennially frozen soil that primarily exists in and around the Arctic and Antarctic regions of the world. While a shallow near-surface soil layer (called active layer) thaws during the summer and re-freezes in the winter, the underlying permafrost remains perennially frozen, often underlying buildings, roads, and other infrastructure.

As warmer temperatures become more common, thawing of permafrost could have major consequences for Alaska. Where thawing has already occurred, dramatic changes in ecosystems and existing infrastructure are evident.  For example, thawing permafrost along the ocean shore and riverbanks in Northern Alaska is causing substantial coastal erosion and is impacting Native Alaska villages and threatening lives and properties.

Despite our current general understanding of how permafrost is changing and may change in the future, it is still very poorly understood how these changes will affect ecosystems and infrastructure on local and regional scales. To help provide this information, scientists are using the Alaska Integrated Ecosystem Model (IEM) to develop possible future scenarios of permafrost changes in the Alaskan Arctic and to estimate areas and rates of permafrost thaw and degradation. Use of the IEM allows us to map past and present permafrost conditions and future permafrost dynamics within the North Slope of Alaska and in the vicinity of the community of Selawik, Alaska.

The permafrost module of the Alaska Integrated Ecosystem Model (AIEM) will be used to establish several high spatial resolution (1km x 1km) and very high resolution (30m x 30m) scenarios of changes in permafrost characteristics in the Alaskan Arctic in response to projected climate change and northern infrastructure development. Impact of these changes in permafrost on northern Alaskan ecosystems and infrastructure will be assessed and regional maps of the possible impacts will be developed.

This project has three related published products:

1. Applicability of the ecosystem type approach to model permafrost dynamics across the Alaska North Slope (Open access, attached below)
   • Thawing and freezing of Arctic soils is affected by many factors, with air temperature, vegetation, snow accumulation, and soil physical properties and soil moisture among the most important. We enhance the Geophysical Institute Permafrost Laboratory model and develop several high spatial resolution scenarios of changes in permafrost characteristics in the Alaskan Arctic in response to observed and projected climate change. The ground thermal properties of surface vegetation and soil column are upscaled using the Ecosystems of Northern Alaska map and temperature data assimilation from the shallow boreholes across the Alaska North Slope. Soil temperature dynamics are simulated by solving the 1-D nonlinear heat equation with phase change, while the snow temperature and thickness are simulated by considering the snow accumulation, compaction, and melting processes. The model is verified by comparing with available active layer thickness at the Circumpolar Active Layer Monitoring sites, permafrost temperature, and snow depth records from existing permafrost observatories in the North Slope region.
      
2. Numerical modeling of two-dimensional temperature field dynamics across non-deforming ice-wedge polygons (Not open access)
   • Ice wedge polygons on the North Slope of Alaska have been forming for many millennia, when the ground thermally contracts in the winter and water fills in the cracks during the snowmelt season. The infiltrated water then freezes and turns into ice. In this paper we investigate temperature dynamics around the ice wedges and surrounding permafrost. A 2-D nonlinear heat equation with phase change is utilized to compute temperature across the ice wedge and surrounding area. Thermal properties of the ground material are estimated by assimilating temperature measurements in the center of ice wedge polygons. The developed finite element model is successfully validated using two analytical solutions and tested in the case of ice wedges located in the tundra area near Barrow, Alaska, where a good agreement between the observed and computed temperatures is obtained. We demonstrate that in order to model temperature dynamics in the ice wedge, the water content above the ice wedge needs to be increased.
      
3. Circumpolar distribution and carbon storage of thermokarst landscapes (Open access, attached below)
   • Thermokarst is the process whereby the thawing of ice-rich permafrost ground causes land subsidence, resulting in development of distinctive landforms. Accelerated thermokarst due to climate change will damage infrastructure, but also impact hydrology, ecology and biogeochemistry. Here, we present a circumpolar assessment of the distribution of thermokarst landscapes, defined as landscapes comprised of current thermokarst landforms and areas susceptible to future thermokarst development. At 3.6 × 10⁶ km², thermokarst landscapes are estimated to cover ∼20% of the northern permafrost region, with approximately equal contributions from three landscape types where characteristic wetland, lake and hillslope thermokarst landforms occur. We estimate that approximately half of the below-ground organic carbon within the study region is stored in thermokarst landscapes. Our results highlight the importance of explicitly considering thermokarst when assessing impacts of climate change, including future landscape greenhouse gas emissions, and provide a means for assessing such impacts at the circumpolar scale.