Quantitative Impact of Organic Matter and Soil Moisture on Permafrost.

Climate warming causes permafrost degradation that not only leads to the release of greenhouse gases to the atmosphere, but also to soil moisture increases due to ground ice melt. These processes are particularly prevalent in peat‐rich and ice‐rich permafrost regions. Peat is important because of its high organic matter content and soil moisture. Although previous work has focused on the importance of two factors, their precise quantitative impact on permafrost is still not clear. Here we apply the Geophysical Institute Permafrost Laboratory model and sensitivity experiments to quantify the role of organic matter and soil moisture on permafrost, with a case study focused on the northeastern Tibetan Plateau. We verify that organic matter and soil moisture has a cooling effect in the warm season and an insulating effect in the cold season. The average thawing onset was delayed 10 days at 0.05–1.4 m depths, when organic matter content increases from 0% to 90%. Freezing onset occurs slightly earlier. Furthermore, active layer thickness (ALT) decreased by 0.40 m. Soil moisture has similar effect on permafrost as organic matter, but ALT changes have a higher magnitude, decreasing by 0.46 m. The results show that both organic matter and soil moisture have an insulating effect on permafrost. Further, the magnitude of impact is larger as organic matter or soil moisture increase. These results can be helpful in assessing permafrost carbon mitigation with climate change. Plain Language Summary: Permafrost can contain high amounts of organic matter and ground ice, and peat plays an important role in permafrost degradation. Permafrost degrades due to climate warming, which can lead to the release of carbon in the form of greenhouse gases, exacerbating the degradation of permafrost. Additionally, soil moisture also significantly impacts permafrost degradation. However, few studies have estimated the effects of organic matter and soil moisture on permafrost degradation. This paper therefore explores the quantitative effect of organic matter and soil moisture on permafrost through a series of model sensitivity experiments. We find that organic matter and soil moisture both insulate permafrost, cooling it in summer and warming it in winter. These results are important for mitigating the effects of climate change on permafrost and carbon feedbacks. Key Points: The insulating effect of organic matter and soil moisture on permafrost is quantified using model sensitivity experimentsIncreasing organic matter and soil moisture both cool permafrost in summer and warm it in winterThese organic matter and soil moisture feedbacks refine our understanding of permafrost dynamics under climate change [ABSTRACT FROM AUTHOR]