The Variability Pattern,Global Linkage Andinfluencing Factors Of Asian Summer Monsoon Over The Past 2000 Years

The past 2000 years cover a series of climate change periods,such as Roman Warm Period,Dark Age Cold Period,Medieval Climate Anomaly,Little Ice Age and Current Warm Period,including the climate change dominated by natural variability before the industrial revolution and the impact of human activities after the industrial revolution.Monsoon changes have caused global and regional climate change,and the Asian summer monsoon transports the heat and moisture of the Indian Ocean and the tropical Pacific,affecting the survival and development of the Asian monsoon region,which accounts for about half of the world's population.In addition,the Asian summer monsoon is linked to climate change of the mid-high latitude in the northern hemisphere and southern hemisphere through the westerlies and the cross-equatorial flow.Therefore,exploring the Asian summer monsoon variability pattern,global linkage and influencing factors in the past 2000 years,is significant for understanding the climate environment background of the weaker human activities before the industrial revolution,revealing the driving,response,feedback and coupling mechanisms of various climate systems on decade-hundred scale,diagnosing the contributions for current global warming of natural variability and human activities,confirming the effects of the internal and external forces on climate change on decade-hundred scale,studying contemporary climate change and predict future climate change.This paper is based on the oxygen isotope record of the WX42B stalagmite in Wanxiang Cave,Gansu Province,with a dating error of less than 5 years and a time resolution of 2.5 years.Here are the main conclusions:1.Compared with accurate,high-resolution Dongge Cave,the Heshang Cave and Sahiya Cave Stalagmite?¹⁸O record in the Asian monsoon region,it is found the Asian summer monsoon in the region was basically consistent within the error range of the dating year in the past 2000 years.That is,t the Asian summer monsoon has shown a weakening trend in the past 2000 years.It has gradually weakened during the Dark Age Cold Period and has reached the strongest during the Medieval Climate Anomaly.During the Little Ice Age,it first weakened and then strengthened.The Asian summer monsoon has weakened considerably during the Current Warm Period.2.By comparing the Wanxiang record with the mean grain size record of the Weinan loess and the Ti content of HuguangnMaar sediments,it is found that the Asian summer monsoon and the Asian winter monsoon are anti-phase over the past 2000 years.The north-south swing of ITCZ caused by changes in solar activity intensity controls this reversed evolution pattern of Asian winter and summer monsoons.3.By comparing the Wanxiang record with the?¹⁸O records of the Greenland ice core,we found that the changes of Asian summer monsoon in the past 2000 years are consistent with the changes of the Arctic polar temperature both in the climate change events and long-term trends,indicating that there is a rapid connection between the Asian summer monsoon and the climate in the high latitude of northern hemisphere in the past 2000 years.According to Arctic sea ice record,the atmospheric?¹⁴C record and total solar radiation record,this connection may be related to the change of solar activity and/or ocean-atmosphere circulation in both regions.By comparing with the NAO records of archives and model reconstruction,we found that the strong Asian summer monsoon is connected with the positive NAO phase,and the negative NAO corresponds to the weakened Asian summer monsoon in the past 2000 years.Comparing the changes of solar activity and Asian winter monsoon in the past 2000years,combined with the telecorrelation between NAO and Asian regions on the interannual scale,it can be inferred that NAO phase change and the strength of the Asian summer monsoon are both elated to the change of solar activity,and NAO phase change can affect the strength of the Asian winter monsoon through the westerlies on the multi-decadal to centennial scale,thus affecting the strength of the Asian summer monsoon.4.By comparing with the Australian KNI-51 record and the Peruvian Huagapo record,we found that the Asian summer monsoon has maintained an anti-phase‘see-saw'relationship with the South American summer monsoon and the Indonesian-Australian summer monsoon in the past 2000 years.The maintenance of‘see-saw'relationship may be related to the north-south swing of ITCZ.By comparing the Wanxiang record with the Antarctic RICE ice core accumulation rate record and the?D record,it is found that the extreme climate change events in Wanxiang record almost match in the Antarctic ice core,i.e.Asian summer monsoon intensification?weakening?event corresponds to rising?falling?temperatures in west Antarctica and increasing?decreasing?sea ice in the southern ocean.It may be caused by climate change in the Antarctic and Southern Ocean,which leads to changes in THC migration rate and ITCZ migration.5.By exploring the effects of solar activity,large volcanic eruptions,and northern hemisphere temperature on the Asian summer monsoon changes in the past 2000 years.It is found that the Asian summer monsoon changes in the past 2000 years are controlled by the solar activity in the decade-hundred scale.The large-scale volcanic eruption on the interannual-decade scale caused a sudden change in the northern hemisphere temperature,thus affecting the intensity of the Asian summer monsoon.In addition,the changes in the Asian summer monsoon in the past 2000 years also have a good correspondence with the number of Arctic sea ice and the North Atlantic ice rafted debris,AMOC,and ITCZ north-south swing.