USA– USGS scientists, in collaboration with researchers at the University of Minnesota and University of Alaska Fairbanks, have mapped belowground permafrost in areas of Alaska that have been affected by wildfire, years-to-decades after the fires occurred. Scientists deploy geophysical equipment in the Nome Creek, Alaska area to assess the effect of wildfire on permafrost. Small electrical signals are injected into the ground through metal stakes connected to the orange cable in the foreground. The measured response is used to detect belowground permafrost conditions. USGS photo, Burke Minsley, 2014.
There has been global concern for many years about the effects of the warming climate on high-latitude permafrost and its vast stores of organic carbon,” said Virginia Burkett, USGS Associate Director for Climate and Land Use Change. When permafrost thaws, carbon currently locked up in the frozen ground is released to the atmosphere as carbon dioxide or methane. Wildfires amplify carbon emissions from declining permafrost in ways we are just now beginning to understand.”
Exceptionally warm and dry weather caused hundreds of wildfires in Alaska and Canada in 2015. Millions of acres of land were burned, causing immediate risk and disturbance to local residents and ecosystems, with plumes of smoke that carried all the way to the lower 48 states.
During two years of extensive field surveys in interior Alaska, the research team combined field observations with geophysical measurements that crossed the boundaries of historical and recent fires to analyze the impacts of wildfire on the underlying permafrost. The impact of fire on permafrost can be highly variable across different landscapes.
Data from the geophysical surveys give us a detailed picture of how permafrost is distributed in the subsurface. This new information helps improve our understanding of how permafrost has changed in response to fire, said Burke Minsley, a USGS geophysicist and lead author of the study.
The geophysical techniques we used can be compared to medical imaging that probes the human body without surgery, Minsley continued. We can see permafrost conditions underground without expensive and disruptive drilling. Data about wildfires and permafrost conditions can be combined with satellite remote sensing observations to help extend interpretations over much larger areas across the state.
Scientists have long known that severe fires can remove the layer of organic material at the ground surface that serves to insulate permafrost and maintain frozen conditions. This study documented locations where permafrost appears to be resilient to disturbance from fire, areas where warm permafrost conditions exist that may be vulnerable to future change, areas where permafrost has thawed, and one location where permafrost appears to be recovering after fire. More information is needed to quantify fire impacts on permafrost in order to assess future vulnerabilities.
The research article was recently published online in the Journal of Geophysical Research: Earth Surface , a journal of the American Geophysical Union.