Based On The LPJ-GUESS Model,the Carbon Cycle Process In The Permafrost Area Around The Arctic Is Simulated

Soil with temperature≤0℃and can exist for at least two years is permafrost,which is widely distributed,mainly in high latitudes and high mountain areas,accounting for about25%of the total land area in the Northern Hemisphere.The extremely low temperature conditions make the organic matter stored in the soil decompose slowly,thus facilitating the accumulation and storage of organic carbon in permafrost soils,making it the largest soil carbon reservoir in the world,and its soil organic carbon reserves account for more than half of the global soil organic carbon reserves.In the context of global warming,the temperature in high latitudes increases by 0.6℃per decade,leading to the melting of permafrost.The large amount of water thickens the active layer of permafrost,which is conducive to the decomposition of organic carbon originally sequestered in the permafrost layer by microorganisms,thus releasing a large amount of greenhouse gases to the atmosphere and producing a positive feedback effect on climate.In this context,the study of the impact of permafrost degradation on the carbon cycle of ecosystems at high latitudes and altitudes has become one of the hot issues in the field of global ecological change.Since permafrost is widely distributed and sensitive to climate change,the storage and release of organic carbon in the circumpolar Arctic plays a key role in the global warming rate,and therefore many scholars have studied the interaction between carbon cycle and climate effects in the circumpolar Arctic.However,the lack of climate and flux data in the circumpolar Arctic and the low accuracy of model simulations have impeded the study of the circumpolar Arctic.Product（NPP）and carbon stocks,which have a strong influence on the carbon cycle,to characterize the carbon cycle in the circumpolar permafrost region.On this basis,three future climate scenario-driven models,RCP2.6,RCP4.5 and RCP8.5,were used to predict the future carbon cycle in the study area and analyze the response of the circumpolar permafrost region to future climate change.The main findings are as follows.（1）The LPJ-GUESS model with parameter localization has good applicability in the circumpolar Arctic permafrost region,and the analysis of the measured and simulated carbon stock data in the circumpolar Arctic region shows that the average correlation coefficient R²=0.80,which can simulate the carbon stock changes in the study area more accurately.The mean correlation coefficient R²=0.78 was found through the analysis of the measured and simulated NEE in the study area,and the overall results were slightly larger than the previous research results through the analysis of NPP simulations,and the overall simulation accuracy of the model was slightly worse in winter,which might be related to the vegetation covered by snow and ice in winter.（2）The overall NEE in the circumpolar Arctic permafrost region during the historical period（2000-2015）showed an increasing trend year by year,showing a carbon sink effect in the growing season and a carbon source effect in the non-growing season;the NPP in the study area showed an increasing trend year by year,with the largest NPP value in the tundra,with a maximum value of 351 g·m^-2·a^-1,and the smallest NPP value in the grassland type,with a minimum value of 32 g·m^-2·a^-1.（3）Both temperature and precipitation in the circumpolar Arctic permafrost region are increasing in the future period（2020-2100）,but the increase varies among climate scenarios.the largest increase is observed in the RCP8.5 scenario,while the increase is flat in RCP2.6and RCP4.5.In terms of vegetation change,the vegetation types in the circumpolar Arctic remain basically the same,but with the increase in temperature and precipitation,the vegetation growth reaches its maximum in 2050 and tends to level off by 2070,which causes significant changes in the distribution of vegetation in the circumpolar Arctic due to different regional climate changes.The prediction of carbon accumulation rate（CAR）indicates that the circumpolar permafrost region is a carbon sink until 2045,and is likely to change gradually from a carbon sink to a carbon source after 2045.The simulation projection of NPP can be concluded that NPP shows an overall upward trend,and the upward trend of the high-emission climate scenario is higher than that of the low-emission climate scenario.