Discussion On The Holocene Climate Change And Optimum Based On The Record Of The Jinfo Cave Stalagmite

Global climate warming and extreme weather events that occuring frequently have seriously affected human's production and life.Climate changing is related to the development of human closely,recognizing the climate evolution model and clarifying the laws of climate development are the foundations and prerequisites for addressing the climate change.However,modern precipitation data accumulated by mankind is only a hundred years,according to archaeological discoveries,the entire Holocene period is a substantial evolution of human civilization development.Relying on a century instrumental data solely,it is impossible to have a clear and macro understanding of climate change over long-term scales,and it is even more difficult to cope with the negative effects of climate change.In the research of stalagmite,relying on accurate U-series dating technology and the carbon and oxygen isotopes,it has been possible to restore the history of climate change over the past 600,000 years.Some scholars have discovered that in the Holocene period during which the civilization evolved,humanities and social life such as the annihilation of the ancient nation and the change of the dynasties were related to abrupt climate change and climate anomalies closely.Therefore,it is necessary to explore the Holocene climate evolution model and its development laws in order to provide a scientific basis for responding to future climate change.In this paper,16 high-precision 230Th datas and 433 oxygen isotope datas were obtained by using the JF13 stalagmite,precise climate evolution sequences were established,and the climate evolution characteristics of each time period were analyzed.At the same time,it compares and analyzes the records of other caves,oceans,lakes,and peat in the Chinese monsoon region were compared and analysised,and the occurrence period of the Holocene Optimum was explored.Get the following conclusions:?1?JF13?¹⁸O records showed that transient monsoon intensive periods and unstable climate events were existed in the Early Holocene.During the Early Holocene?10.5⁸.0 ka BP?,the fluctuation range of oxygen isotope value was -9.47^-8.05,with a changed range of 1.42‰and the average value was-8.83‰.Judging from its changing trend,JF13?¹⁸O has been become negative from 10.4 ka BP largely,and reached the peak of the early Holocene at 9.8 ka BP,and then changed steadily until 9.0 ka BP;During the period from 10.0 to 9.0 ka BP,the?¹⁸O curve was at a high level overall,indicating that the monsoon was strong at this time.Since then,the monsoon has quickly declined.During the period of 9.0⁸.0 ka BP,the?¹⁸O curve showed a"W"type,indicating that the monsoon was extremely unstable and there was a series of climate abrupt events.Therefore,the early Holocene had both a short period of monsoon prosperity and an unstable period.?2?JF13?¹⁸O records showed that the monsoon re-enhanced during the Middle Holocene.During the Middle Holocene?8.0⁴.0 ka BP?;The fluctuation range of oxygen isotope value was-9.60^-7.49,with a changed range of 2.11‰and the average value was-8.66‰.With theweakening of solar radiation,the value of JF13?¹⁸O became positive gradually.However,the JF13?¹⁸O curve did not decrease synchronously with the weaken of solar radiation,the?¹⁸O curve increased again after the 9.0⁸.0 ka BP climate fast wave event end,and the most negative value of the whole Holocene period?-9.60‰?was reached near 7.5 ka BP,indicating that the monsoon was strengthened once again and reached its strongest state,the duration of the strong monsoon was nearly 2 ka?8.0⁶.0 ka BP?.This period corresponds to the classic mid-Holocene optimum period.After about 6 ka BP,the monsoon weakened gradually,and the monsoon strong period disappeared.?3?During the Early and Middle Holocene periods,there was a strong monsoon period;in terms of monsoon intensity and duration,the Middle Holocene was more suitable than the early Holocene.In the Chinese monsoon region,oceans,lakes,peat,and other records recorded strong monsoon periods in the Early and Middle Holocene,which were the same as those recorded by JF13?¹⁸O.The?¹⁸O curve of the stalagmite showed a peak near the 9 ka BP in the early Holocene and 7.4 ka BP in the Middle Holocene,respectively.Indicating that there were periods of strong monsoon during the Early and Middle Holocene.As a whole,the Mid-Holocene monsoon boom period was longer than the Early Holocene,and the most negative peak of the entire record also appeared in the Middle Holocene.Although stalagmite?¹⁸O records showed that the monsoon increased rapidly during the early Holocene,it was hampered by a series of weak monsoon events during the enhancement process,which not only reduced the duration of the monsoon,but also weakened the monsoon growth intensity.In the Middle Holocene,the monsoon became more stable and strong.?4?The strength of the East Asian monsoon is closely related to solar activity and the zonal changes in the climate.Calculation displaied that the JF13?¹⁸O records were highly correlated with the Greenland ice core records and Ti content curves in the Cariaco Basin of Venezuela,South America.It was found that the JF13?¹⁸O records have periods such as 770a,526a,476a,384a,277a,238a,143a,80a,65a,and 53a.Through power spectrum analysis,indicating that the high latitude climate in the northern hemisphere,ITCZ movement and solar activity all affected the intensity of the East Asian monsoon...