资源环境科技发展态势分析平台

Scientists from the U.S. Geological Survey completed a multidisciplinary field study near Fairbanks, Alaska, to better understand how belowground properties, such as liquid water and ice within the soil, influence permafrost thaw, microbial production of GHG and surface gas  emissions. The study took place at a site where some of the permafrost has already thawed, causing the ground to collapse and become what is called a collapse-scar bog.  

Snow blankets vulnerable permafrost at the Alaska Peatland Experiment site near Fairbanks, Alaska. A new study has found liquid water in frozen soils may be a significant driver for advancing permafrost thaw, controlling cold-season carbon emissions, and enhancing the microbial release of carbon prior to permafrost collapse. 

(Credit: Stephanie James, USGS. Public domain.)

The USGS researchers found that permafrost at the bog edges is very warm, just below 32 degrees Fahrenheit (0 degrees Celsius), and contains substantial liquid water as well as methane concentrations significantly above atmospheric levels. This suggests permafrost may be able to support microbial activity and greenhouse gas production before the soil has completely thawed. Since permafrost and frozen soils are typically not considered significant sources of greenhouse gases, these results could impact climate models and the global carbon budget. However, the fate of this permafrost methane remains uncertain, and additional research is underway to quantify the magnitude of carbon losses from frozen soils.  

The study also demonstrates how passive seismic monitoring in the wintertime offers a unique opportunity to monitor subtle changes in water and ice content within the seasonally frozen soils, which are extremely difficult to measure with traditional techniques and at large spatial scales. As wintertime air temperature fluctuates, increases in liquid water within soils correlate with boosts in carbon dioxide (CO2) released at the surface. These slightly warmer and wetter conditions within the soils may be stimulating overwinter microbial respiration, leading to elevated CO2 production. Soils nearer to the bogs showed a period in early winter where the opposite was observed, indicating ice formation coincided with increased CO2 emissions and may be direct evidence of ice formation squeezing gases out of the soil.  

This study demonstrates a new way of understanding changing permafrost landscapes and shows frozen soils may be more dynamic and alive than previously thought.   

The Biophysical Role of Water and Ice Within Permafrost Nearing Collapse: Insights From Novel Geophysical Observations - James - 2021 - Journal of Geophysical Research: Earth Surface - Wiley Online Library  

This material is based upon work supported by the National Science Foundation under Award No. 1725625. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. This work was also funded by the USGS Land Change Science program and Climate Research and Development program. The study site is managed by the Bonanza Creek Long-term Ecological Research, which provided vital assistance and support.