February 14, 2020
Buried Ice in Old Permafrost May Melt More Quickly Than in New Permafrost
Numerical simulations suggest that tundra landscapes affected by older, larger ice wedges may be more prone to rapid permafrost degradation and surface deformation.
Much of the northern permafrost zone contains ice wedges, or large bodies of buried ice, within a couple meters of the ground surface. New modeling results indicate climate change may cause older, larger ice wedges to melt before younger ones, altering surface topography and ecosystem functioning.
The modeling results suggest that landscapes with older, larger ice wedges are among the most vulnerable to climate change. This finding may help improve global-scale assessments of the permafrost-climate feedback by improving the representation of tundra landscapes in earth system models.
Across the Arctic, an area ten times the size of Britain is underlain by large bodies of nearly pure ice, known as ice wedges. In recent years, climate change has caused many ice wedges to start melting from the top down, causing depressions known as thermokarst troughs to develop at the surface. These thermokarst troughs often fill with water, while the surrounding soil becomes better drained, thereby altering rates of carbon dioxide and methane emissions from the landscape. We constructed a numerical model of thawing processes beneath developing thermokarst troughs to assess factors controlling permafrost vulnerability. The results indicate that thaw intensity is strongly impacted by trough width. The permafrost beneath wide, flooded troughs may degrade much more rapidly than the permafrost beneath narrow troughs, due to a contrast between the efficiency with which ponded water absorbs solar radiation and sensible heat in summer, and the inefficiency with which that energy is released back to the atmosphere in winter, often via conduction through the adjacent, non-inundated sediments. Additionally, the permafrost beneath wide, flooded troughs may be more sensitive than other permafrost to changes in winter air temperatures and snow depths. These findings are important because they imply that areas of old permafrost (i.e., areas that haven’t been affected by recent erosion or sedimentation), which tend to have the largest and widest ice wedges, may be the most vulnerable to rapid changes in ecosystem functioning caused by ice wedge degradation as air temperatures rise. The sensitivity of wide ice wedges to winter conditions is important, because in many areas of the Arctic, changes to winter air temperatures and snow depths have been even more pronounced than changes to summer air temperatures.
Los Alamos National Laboratory
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
- Next Generation Ecosystems Experiments Arctic (NGEE-Arctic) project (DOE ERKP757), funded by the Office of Biological and Environmental Research (BER) in the U.S. Department of Energy’s (DOE) Office of Science.
- NASA Earth and Space Science Fellowship program, for an award (80NSSC17K0376) to the lead author.
Abolt, C.J., et al. "Feedbacks between Surface Deformation and Permafrost Degradation in Ice Wedge Polygons, Arctic Coastal Plain, Alaska." JGR Earth Surface 125 (3), e2019JF005349 (2020). https://doi.org/10.1029/2019JF005349.