Lead Isotopic Deposition Responds Environmental Changes In The Hani Peat Of Northeastern China

As a geological information carrier,peat plays a vital role in the study of environmental changes.The northeastern region of China is located at the intersection of the summer monsoon and the northwest winter monsoon in the southeast,which is a sensitive zone for global change.The importance of studying peat is more significant.Recent years,Chinese scholars have gradually paid attention to the study of environmental change.However,the study of heavy metals and their isotopes in peat is still relatively weak.Northeastern Hani peat is an ombrotrophic peat that mainly accepts atmospheric sediments and continues to accumulate tens of thousands of years to record the changes in atmospheric heavy metals in detail.Therefore,this paper takes the Hani peat samples from Liangshui Township of Jilin Province as research object,and collects305 samples of peat,using AMS-¹⁴C dating,ICP-OES,ICP-MS and MC-ICPMS to analyze the main trace elements and lead isotope.Preliminary study on lead isotope composition and provenance identification in annual scale peat,exploring the possibility of lead isotope indicating important environmental events in the Northeast for many years and it comes to conclusions below:1.The sedimentary age of the northeast Hani peat column with a depth of 915 cm is 14567 years.The lead isotope composition change in peat deposits was ²⁰⁶ Pb/²⁰⁴ Pb=18.221-19.107,²⁰⁷ Pb/²⁰⁴ Pb=15.601-15.696,²⁰⁸ Pb/²⁰⁴ Pb=38.364-39.068.Through the normalization of lead isotope,five important time periods are divided,and segment b is subdivided into segments b₁,b₂ and b₃.A section 0-60cm?current-533B.P?,b₁ section 90-156cm?674-1571B.P.:corresponding to the Western Jin Dynasty to the end of the Yuan Dynasty?,b₂ section 156-195cm?1571-2269B.P.:corresponding to the Western Jin Dynasty to Qin Dynasty?,b₃ segment 195-210cm?2269-2523B.P.:corresponding to the Qin Dynasty to the Spring and Autumn Warring States?,c segment285-300cm?3558-3900B.P.?,d segment 489-606cm?8223-9635B.P.?,e-segment 645-660cm?10368-10624B.P.?.2.The lead isotope ratio(²⁰⁶ Pb/²⁰⁷ Pb)in the a section of the peat column showed a downward trend?1.189-1.168?;the b segment rose in the first stage?1.181-1.191?,and increased in the second stage?1.186-1.191?and then decreased?1.191.-1.185?.To the initial value,the 3 segments slowly descended?1.192-1.181?,the c segment showed a small valley?1.192?,the d segment showed the largest peak?1.217?,and the e segment showed a smaller peak?1.202?.By comparing the lead isotope data of atmospheric aerosols,lead-zinc ore,loess and other samples in the northeast and surrounding cities,combined with the mixed model,the potential sources of Hani peat lead are mainly local soil weathering,northwest desert,loess plateau paleosol,and industrial activities and the long-distance lead pollution source have less impact.The endmember contribution is subject to further evaluation.3.Section a is located at the top,and its change is greatly affected by the surface;Section b may experience changes in the intensity of the northwestern winter wind;Section d reveals the activity of the Tianchi volcano in Changbai Mountain.4.d lead isotope anomaly indicates the volcanic eruption of Changbaishan Volcano in the 8233B.P.-9635B.P.;compared with the previous temperature data,it is found that there is a strong coupling relationship between the two above.