The Mechanism In Response Of Organic Carbon-Rich Permafrost To Climate Change

Under the background of globing warming,the change and development of cryosphere have attracted extensive attention.The significant rise of global temperature leads to the degradation of permafrost in cold regions.Due to the influencing factors including organic carbon,the pattern of permafrost degradation presents spatial heterogeneity.In addition,the organic carbon in permafrost is released by greenhouse gases such as carbon dioxide and methane in the process of degradation,which exacerbates climate warming.Therefore,organic carbon plays an important role in permafrost degradation and carbon cycle by affecting soil thermal characteristics and hydrological processes.In order to explore the mechanism in response of organic carbon-rich permafrost to climate change,we selected field observation sites with great differences in soil texture in the permafrost area in the upper reaches of Heihe River Basin.EBo TA site in Eboling is rich in organic carbon,and PT5 site in Yeniugou is mainly mineral soil and less organic carbon content.Based on the differences between two sites,we compared the permafrost degradation through measured data,numerical simulation and sensitive experiments to explore the response mechanism of permafrost rich in organic carbon to climate change.The following conclusions are obtained:(1)The research of field measured data shows that the soil temperature difference at each depth of the two sites(soil temperature of EBo TA site minus PT5site's)presents a negative value in warm season,the temperature difference variation range is about-9.9–0 ?.While the cold season is positive and the temperature difference variation range is 0–12.3 ?.Generally,the thaw onset of EBo TA is later than that of PT5,and the freezing onset is the opposite.The freezing period of EBo TA is longer than that of PT5 and the thawing period is shorter than PT5.Compared with PT5,the freezing days of EBo TA are about 19–119 days more and the thawing days are 19–119 days less.In addition,the active layer thickness(ALT)of PT5 is greater than EBo TA,and the mean annual ground temperature(MAGT)of PT5 is higher than EBo TA.According to the field measured data,we can conclude that organic carbon has a certain protective effect on permafrost.(2)With the help of the Geophysical Institute permafrost Lab(GIPL)model and the Coupled Model Intercomparison Project Phase 6(CMIP6),this research explores the response mechanism of organic carbon-rich in permafrost to climate change in the future.The results show that the soil temperature change trends of the two sites at different depths are different.In the historical period,the monthly trends of soil temperature at EBo TA and PT5 are about 0–0.007 ?/yr and 0.001–0.006 ?/yr respectively.In the future scenario,the monthly trend of EBo TA is expected to be 0–0.062 ?/yr,and PT5 site's monthly rising trends of soil temperature is about 0.004–0.076 ?/yr.In addition,the change trends of deep soil temperature of PT5 are greater than that of EBo TA under each scenario in the future.In the seasonal variation trend of soil temperature at the two sites,the warming range in winter is greater than that in summer at some depths,but the warming range of EBo TA is lower than that of PT5.It is found that the active layer thickness deepening rate of PT5 in the future scenario is always higher than that of EBo TA.In addition,there is talik at PT5 in all future scenarios,but at EBo TA only in SSP5-8.5 scenario.Comparing the permafrost degradation of the two sites with the relevant variables of permafrost,the higher organic carbon content leads to the slower response of EBo TA site to future climate warming compared with PT5.(3)The effects of organic carbon and soil moisture on permafrost are quantitatively described by numerical model and sensitivity experiment.Organic carbon and soil moisture are important factors affecting the response of permafrost to climate change.This research only selects PT5 site to study.The results show that the higher organic carbon and volume water content of soil moisture,the greater the soil temperature difference between control experiment and sensitive experiment.The soil temperature difference caused by organic carbon content is negative and large in warm season,but positive and small in cold season.With the increase of organic carbon content by 10%,the thawing and freezing onset are delayed by 11 days and 1day averagely,and the ALT becomes shallower by 0.42 m.When the volume water content increases by 10%,the thawing onset is delayed by about 15 days on average,and the freezing onset changes little.At the same time,the ALT becomes shallower by0.46 m.Based on the results of sensitive experiments,it can be concluded that organic carbon and soil moisture can slow down the permafrost degradation to a certain extent.In conclusion,this research is based on the field measured data,numerical model and sensitive experiments.It is concluded that EBo TA site has a slower response to climate change than PT5 site.This may be because soil organic carbon has lower thermal conductivity and higher soil water content than mineral soil.Therefore,the thermal insulation layer will slow down the heat transfer rate of soil and atmosphere.It is verified that organic carbon can protect permafrost and provide technical support for further exploring carbon cycle in permafrost.