Stepwise Change Of The East Asian Monsoon In The Holocene

The Holocene is an important period for the evolution of human civilization and an important period for studying the relationship between climate change and the development of human society.In the Asian monsoon region,the stability of the monsoon climate is an important factor affecting social,cultural,and historical dynasties.Therefore,the evolution of the Holocene East Asian monsoon and the abrupt change of the millennium scale are the focus of scientific research.The Holocene is a typical interglacial period.A prominent feature of climate evolution during this period is the existence of a series of millennial-scale abrupt climate events,such as the Holocene rapid climate change event?RCC?and the high-latitude Bond event.A large number of Asian monsoon reconstruction records indicate that during the Holocene,the monsoon intensity was dominated by solar radiation at the orbital scale,but unlike the smoother change of solar radiation intensity,some studies have shown that the monsoon intensity has a stepwise change during this period.It implies that there may be a threshold effect of monsoon changes,and the complicated change of monsoon may be an important driving factor for human migration,civilization change,and the collapse of ancient society.Therefore,the gradually weakening solar radiation and the resulting ocean-atmosphere nonlinear feedback process directly or indirectly trigger the sudden event of Asian monsoon?Whether the stepped nonlinear response phenomenon of monsoon changes throughout the Holocene and whether it has universal significance still needs further study.This paper reconstructs the evolution of the Asian monsoon since Holocene through a stalagmite HF01 record collected from the Heifeng Cave in the Jinfo Mountain area of Chongqing,a typical monsoon region of China.The Rampfit regression analysis method is used to perform multi-segment fitting analysis on Holocene stalagmite records.At the same time,the geological carriers in other regions are used to explore the characteristics of the stepwise change of the Asian monsoon intensity during the Holocene.Through a comparative analysis with the recording curve that characterizes the climate of the North Atlantic,and the data processed by Past 3.5 software,we briefly discuss the possible differential response mechanism of the Asian monsoon to the cold events in the North Atlantic at the millennium scale during the Holocene.Concluded as follow:?1?The change trend of the stalagmite HF01?¹⁸O recorded in the Ordovician cave in Chongqing on the orbit time scale is basically consistent with other stalagmite records in the Chinese monsoon area,following the trend of Holocene solar radiation in the northern hemisphere.The stalagmite HF01 recorded a"w"type monsoon oscillation event that lasted at least 500a during the8.5?8.0 ka BP period of the end of the early Holocene.This climate fluctuation event is different from 8.2 ka event in time and duration as the previous study,and the stalagmite,peat and other records in the monsoon area are all imprinted,indicating that the monsoon's decline in the late early Holocene is universal in the monsoon area.To a certain extent,it hindered the overall enhancement process of the early and middle Holocene monsoon and interrupted the continuous strengthening trend of the early Holocene monsoon.Therefore,the early Holocene monsoon was not stable and strong.?2?Through the Rampfit regression analysis method,the HF01?¹⁸O record was analyzed by multi-stage fitting,and it was found that the stalagmite oxygen isotope changes have a significant step change trend,and the overall can be divided into six equilibrium states?Step1?6?and five transition states?Transition1?5?.Using the Bayesian analysis method,the five transition states?T1?T5?of HF01 can be verified by the posterior of the Bayesian analysis method.The posterior probability of the T2 conversion stage is the highest,reaching 66%,and T1?50%?,T4?52%?and T5?48%?have posterior probabilities of around 50%,and T3 has a relatively small posterior probability?38%?.The Bayesian mathematical algorithm supports our viewpoint of the existence of six equilibrium states and five transition states in the Holocene monsoon state.The Rampfit analysis results verify that the most significant feature of the stalagmite HF01 record is that the Holocene monsoon change has a non-linear,stepwise change characteristic.That is 1)In the early Holocene,the continuous accumulation of solar radiation,stimulated the monsoon state to break through its change threshold and produced a sudden jump,resulting in the monsoon in the early Holocene in a two-stage stepped form;2)In the late Holocene,as the solar radiation continued to weaken,the monsoon state continued to exceed its declining threshold during this period,making the monsoon change exhibit a three-stage stepwise weakening change pattern;3)Comparison runs through the north and south of the Chinese monsoon area Geological records referring to the monsoon found that the morphology of the early Holocene monsoon is more complicated.The stalagmite record indicates that the monsoon is increasing stepwise,while the lake record believes that the monsoon fluctuates greatly at this time,and there are several monsoon instability events.The monsoon records in the north and south after the mid-late Holocene all showed a stepwise weakening pattern,which indicates that the stepped monsoon change pattern is universal in the Chinese monsoon region.?3?In comparison with the content of hematite in the North Atlantic cold event?Bond event?,it is found that the Holocene weak monsoon event recorded by the stalagmite HF01?18O sequence has different morphologies in the early Holocene and mid-late Holocene.In the early Holocene,the weak monsoon event has two processes:weakening of monsoon and strengthening of recovery;the weak monsoon event of the middle Holocene only has the process of weakening of monsoon,and there is no obvious monsoon recovery stage.The Holocene monsoon state transition seems to be the result of the combined effect of solar radiation and the Bond events of the North Atlantic,but the role of solar radiation in different stages is different.The Bond events are closely related to the East Asian monsoon weakening event,but there are also differences.During the Holocene,the Bond events are reciprocating,and the temperature can be recovered after each Bond event;while in the Asian monsoon area,the mid-late Holocene weak monsoon event is one-way weakening.This shows that the intensity of solar radiation has an important influence on the recovery of the weak monsoon event caused by the Bond event.The spectrum analysis results further confirmed that the threshold effect of the monsoon stepwise change is the result of the combined effect of the cumulative change in solar radiation and the cold events in the North Atlantic at the millennial scale.