The Significance Of Atmospheric Precipitation And Stalagmite ?¹⁸O In The Asian-australian Monsoon Region:Integration Of Observed And Natural Records

The internal variability of the Earth's climate system has always been a hot topic among the community of global climate change.Because of the limitations of the timescale of the instrumental data,it only provides the instrumental data of the change of the ocean-atmospheric circulation over the past 100 years.However,for the change of millennium-scale climatic regulation commonly relied on geological proxies?e.g.ice cores,cave stalagmites,tree rings,etc.?,and high-resolution paleoclimatic records generally were used to reconstruct the change of El Ni?o-Southern Oscillation?ENSO?.Throughout the study of ENSO variability in the past few decades,we have found that the internal variability of ENSO reconstructed by different geological indicators,and the results of different researchers are also contradictory,which have also added the uncertainty for the study of ENSO variability on the longer timescales.In order to have a thorough understanding of the ENSO modality of the past millennium and reduce the uncertainty of the reconstruction of the ENSO variability over the past millennium,this paper will begin from the new perspective of the Asian-Australian monsoon system and combined with the signal of?¹⁸O from the atmospheric precipitation to the cave stalagmite in the Asian-Australian monsoon region.We use the U-Th dating stalagmite samples in Asian-Australian monsoon region,and propose a new ENSO indicator——stalagmite?¹⁸O.Simultaneously,we will systematically compare and explore the history of ENSO over the past millennium with the external variability of the Earth system and other atmospheric oscillations,and explain the relationship between the internal and external variability of the Earth system.We mainly draw the following preliminary conclusions:?1?The monthly precipitation of meteorological sites in the Asian-Australian monsoon region is inversely related to the oxygen isotope of atmospheric precipitation,and all monitoring sites can pass the correlation test,which indicates this regulation is common in the Asian-Australian monsoon region.Therefore,the?¹⁸O of atmospheric precipitation mainly reflects the change of local precipitation in term of the mathematical statistical results on the monthly timescales.However,the change of precipitation at all monitoring sites in the Asian-Australian monsoon region may not be the most direct factor resulting in the change of oxygen isotope,and the value of atmospheric precipitation?¹⁸O was dominated by the changes of atmospheric circulation and local water vapor sources in different seasons.?2?The East Asian monsoon and Australian monsoon regions were affected by the composite water vapor source,and the annual weighted average of the atmospheric precipitation?¹⁸O is not correlated with the local annual precipitation on the inter-annual timescales,but the annual precipitation of the Indian monsoon region affected by the single water vapor source,and the annual weighted average of the local atmospheric precipitation oxygen isotope are inversely correlated with local precipitation on the inter-annual timescales,therefore,when we used stalagmite oxygen isotope to reconstruct local precipitation changes,we should keep cautious attitude in the East Asian monsoon and the Australian monsoon regions.In addition,the oxygen isotope of atmospheric precipitation in the Asian-Australian monsoon region has a good correlation with the ENSO index on the inter-annual timescale.Although the reason is still controversial,the significant correlation between the atmospheric precipitation oxygen isotope and the ENSO index provided the basis for reconstructing the ENSO change index over the past millennium.?3?It can be found from that there is a certain correlation between the stalagmite?¹⁸O records of the Asian-Australian monsoon region,which indicates that the record of stalagmite?¹⁸O is consistent over the decade-hundred-year timescales in the Asian-Australian monsoon region,therefore,the stalagmites?¹⁸O in this region may be controlled by the same climate signal.In addition,the stalagmite?¹⁸O records in the the Asian-Australian monsoon regions are roughly same trend during the Little Ice Age?LIA?period,which is contrary to“seesaw model”of the northern and southern hemispheres.?4?By integrating the?¹⁸O of stalagmites record over the past 1 ka,it can be found that the?¹⁸O of stalagmites in the LIA period show a significant positive trend,which corresponds to the El Ni?o state of the Ni?o 3.4 zone in the tropical Pacific Ocean.The stalagmite?¹⁸O in the medieval warm period was obviously negative,which corresponds to the La Ni?a state of the Ni?o 3.4 region of the tropical Pacific Ocean.In order to verify the reliability for the integrated ENSO results of stalagmites,we also compared the measured SOI index with integrated ENSO index,and found that there is an obvious inversely correlation between oxygen isotope of atmospheric precipitation and SOI index,demonstrating that the integration results are reliable and correctly reflect the change of ENSO.?5?There is a significant anti-correlation relationship between the ENSO index reconstructed by the stalagmite?¹⁸O and the solar activity index in the Asian-Australian monsoon region.The reason is that solar activity may affect the sea surface temperature?SST?in the tropical east and west Pacific regions.In addition,by comparing the reconstructed PDO index with the ENSO index in the Asian-Australian monsoon region,it can be found that there is a significant positive correlation between the ENSO and PDO,and the SST in the tropical Pacific Ni?o 3.4 via the“Atmosphere Bridge”affecting the change of PDO.In addition,the AMV index is inversely related to the reconstructed ENSO index over the past 1ka.When the SST of the mid-high latitude cools down in the North Atlantic,it corresponds to the positive anomaly of the SST in the tropical Pacific Ni?o 3.4.This teleconnection relationship was realized by the Atlantic meridional overturning circulation?AMOC?and atmospheric Rossby wave.