Application Of Subtropical Tree Rings In China To Excavate Past Unconventional Climate Signals

In the past 100 years,with the global warming,the contradiction between human beings and the environment has become more prominent.As a significant impact area of global environmental change,it is extremely urgent to understand the past climate change situation in China and reveal the laws of climate change in the past.As one of the most important high-resolution climate proxy,tree-ring data plays an important role in the climate reconstruction process over the past hundreds and thousands of years.Numerous studies have shown that tree-ring data has great potential for studying past climate change in subtropical regions of China.However,due to the complexity of climatic conditions in subtropical regions,the annualization of tree rings in this region is more difficult than in arid and semi-arid regions.At present,most of the relevant researches use tree rings to reconstruct some of the conventional climate indicators in the historical period,such as mean temperature and precipitation,which greatly limits the development of subtropical dendroclimatology in China.This paper uses the tree-ring samples and ring width data of Dabie Mountains in the subtropical region of the border between Hubei Province,Henan Province and Anhui Province,Changting County of Fujian Province,and Suichang County of Zhejiang Province.Five tree ring width standardized chronologies were established based on principles of dendroclimatology research in three regions,and correlation analysis,first-order differential correlation analysis,sliding correlation analysis,spatial correlation analysis,power spectrum analysis and other methods were used to study the relationship between the radial growth of trees and climatic factors,and meteorological data such as soil temperature and sea surface temperature obtained from different pathways were used to explore the role of subtropical tree rings in excavating past unconventional climate signals,and finally reconstructing the soil temperature and sea surface temperature in corresponding regions.In order to analyze the relationship between trees growth and climate in the Dabie Mountains,Three standardized tree ring width chronologies naming HZS,BDF and ZRFYJO were established by collecting tree ring samples in the field,which were analyzed with mean temperature and precipitation in the nearest Macheng weather station and soil temperature data obtained by the China Meteorological Administration.The results of the analysis indicated that the correlation between the HZS and BDF chronology sequences and the climatic factors was significantly weaker than the ZRFYJO chronology.The difference in this response relationship might be due to the apparently different altitudes between the sampling sites.The ZRFYJO chronology sequence showed a significant positive correlation with the 10 cm soil temperature before and after the first-order differential treatment,which indicated that soil temperature was the main limiting factor for trees growth in this region;The MTJ chronology was established using the tree ring width samples collected from Changting County,and The relevant analysis results showed that the chronology and the sea surface temperature in the northern part of the South China Sea showed a significant positive correlation both at high frequency and at low frequency.The XDC chronology was established using ring width data of Suichang County obtained from The International Tree-Ring Data Bank.The analysis results showed that trees growth in this area showed a significant negative correlation with the sea surface temperature in the western Pacific warm pool area before and after the first-order differential processing.By comprehensively analyzing the correlation between the ZRFYJO,MTJ and XDC chronological sequences and the mean temperature,it was also found that the lags and height differences between the sampling sites make the three chronology sequences different in response to the mean temperature.Based on the above correlation analysis,the method of linear regression were used to reconstruct the history soil temperature of the Dabie Mountain,the sea surface temperature of South China Sea and the sea surface temperature of western Pacific warm pool in the three regions.The reconstructed soil temperature sequence was highly consistent with the changes of the actual observation sequence,and passed the test of sliding correlation analysis.Power spectrum analysis and spatial correlation analysis indicated that the change of soil temperature in the historical period of the Dabie Mountains might be affected by ENSO and Southern Annular mode.The reconstructed sea surface temperature of South China Sea sequence and the actual observation data showed a high spatial correlation,indicating that it had better captured the wide range of sea surface temperature changes.The reconstructed sea surface temperature sequence of western Pacific warm pool region also reflected the variation of sea surface temperature in the extensive western Pacific region,and we also found that the historical period of reconstruction had a certain impact on precipitation in eastern China.The study in this paper provides a method for reconstructing past unconventional climate indicators of past soil temperature and sea surface temperature based on tree-ring,indicating that tree rings in subtropical,especially eastern coastal areas of China have great potential for excavating past unconventional climate signals.Reconstructed soil temperature and sea surface temperature data can also serve future agricultural and forestry production practices.