| Terrestrial ecosystems are important carbon sinks,offsetting about one third of the fossil fuel emissions,which largely affect the concentration of carbon dioxide in the atmosphere.There are large interannual variations(IAV)in global land carbon sink,and understanding the driving mechanism is a key issue for carbon cycle research and future climate change predictions.At present,there have been some good research on the global land carbon sink IAV,but the contributions of different regions,different climate factors and different time periods to global carbon sink IAV are still under debate.In view of this,this paper proposes a more objective and refined regional division method to analyze the relative contributions of different regions to the global land carbon sink IAV.Based on the refined zoning scheme,this paper explores the impact of regional water and heat variation on the global land carbon sink IAV.Finally,this paper uses the critical time period analysis and vegetation growth carryover(VGC)analysis to explore the impact of different time periods in the growth period.This research will deepen the scientific understanding of the IAV of land carbon sink.The main conclusions are as follows:(1)Using different drought indicators and different data sets to analyze the regional contributions of global carbon sink IAV,most of the results show that compared with the semi-arid areas,the warm and humid areas contribute more to the global land carbon sink IAV(the results of some drought indicators and data sets show that the two contribute equally).At the same time,according to the contribution of each grid unit to the IAV of global land carbon sink,the results show that the regions with larger contribution value have higher average temperature and precipitation,which confirms the importance of warm and humid regions to the IAV of global carbon sink.At present,the mainstream view focuses on the importance of semi-arid areas to the IAV of global carbon sink.This article emphasizes the importance of humid regions based on more data sets and more refined regional division method.(2)The relationship between climate factors and global carbon dioxide growth rate(CGR)is studied in different ways.The results show that the IAV of temperature and global CGR in different regions are positively correlated,and the regional difference is small.The correlation between terrestrial water storage(TWS)and global CGR in different regions is relatively large,with negative values in most regions and positive values in some regions(such as subtropical regions with annual average temperature of 16-20℃).Among the Trans Com 3 subregions,the IAV of global land carbon sink is most correlated with the variation of water and heat in tropical South America.In addition,the IAV amplitude of water and temperature will also affect the regional contribution to the global land carbon sink.The greater the variation of water is,the greater the contribution is,while the greater the variation of temperature is,the smaller the contribution is.(3)Based on the global and site scales,the IAV of land carbon sink in different time periods is explored.The results show that on a global scale,the critical time period of TWS influencing the IAV of global CGR is shorter than that of temperature,mainly in spring and early summer in the northern hemisphere.At the site scale,the temperature and precipitation in the critical time period can explain the IAV of net ecosystem carbon exchange(NEE)better than the average value of the whole year,early growing season(EGS),peak growing season(PGS),late growing season(LGS)which divided by the gross primary productivity(GPP)curve.It is not the long-term average climate that most affects NEE IAV,but the shortterm climate anomalies.The critical time period of precipitation affecting the IAV of carbon sink is earlier than that of temperature.In addition,EGS has a significant impact on the IAV of net ecosystem exchange(NEE)in PGS,and EGS and PGS have a greater impact on the IAV of NEE,especially in PGS. |
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