| As human beings living in the earth system,the changes of earth environment are closely related to the development of human society.In order to obtain better survival and development conditions,people are eager to understand and control the law of global environment and climate change,expect to predict the trends,magnitude and impact of future environment and climate changes,and try to solve the problem with human wisdom and technical means.For this reason,global change research has become the important topic which needs to be explored urgently.The Past Global Changes research(PAGES)is important branch of global change research,which is aimed to predict and access the information of future global environmental changes by studying the past climate and environmental changes,and providing strategic support for human sustainable development.The study of restoration or reconstruction on paleoclimate and paleoenvironment through various deposition materials and information carriers are important means to understand and explore the laws or mechanisms of global environmental system changes,which are also the important research direction of global change studying.In the past historical development process,the Holocene(since 11500 years ago to the present)is the youngest geological epoch which is also important period for the development and prosperity of human civilization.During the Holocene,the global climate and environment transformed frequently and rapidly bringing in great changes for human environment.In the process of past climate and environment change,the climate of the past thousands years is the most similar to the future climate change.The climate of the past ten thousand years reflects the natural background superimposed with human activities interference,which not only reflects the natural laws of climate change,but also records the impact of human activities.Therefore,the study of Holocene climate and environmental change is not only the need of human sustainable development,but also important way to predict future global change by understanding the past earth environment evolution,which is of great significance to human beings.Then it is critical to acquire continuous material that has fully recorded information about the Holocene climate and environment change.Peat is kind of soft organic sediment with different decomposition degree which always formed in the Quaternary or the Holocene.The formation process of peat would be affected by different climate,hydrological and other environmental conditions.As information carrier for environmental evolution,peat has proven to be important repository and archives for climate change just like ice cores,loess or lake sediments.Compared with other sediments,peat shows the advantages of acquiring easily and economically,deposition continuous and fast,long time scale recording,substitute indicators used widely and so on.So it is the ideal archival material for studying of past climate and environment changes,and it shows unique value in the absence of historical records,ice core,tree wheels or coral reefs records.In this paper,the Hani peat sediment from Northeast China is chosen as the research object.By extracting and analyzing the paleoclimate and environmental substitution indicators from Hani peat,we discussed the paleoclimate significance of the substitution indicators and reconstructed the process of climate and environmental changes of Northeast China since the Holocene.Meanwhile,the atmospheric mercury content and mercury deposition flux that recorded by Hani peat were measured.And the history of atmospheric mercury deposition since the Holocene has been restored.It studied the responses of atmospheric mercury deposition in Northeast China to the Holocene climate changes and volcanic eruptions while the possible internal mechanism had been discussed as well.The research provides new ideas for the global change studying on peat archives.The main contents and research results of the paper are as follows:1.First of all,it introduces the research progress of peat paleoclimate and environment changes at home and abroad through the study on peat chronology,peat climate and environment indicators,the history of atmospheric mercury deposition and volcanic eruptions recorded by peat.Meanwhile,it gives discussion and elaboration on the formation and distribution of peat,the research methods and advantages of peat paleoclimate studying,the basic physical and chemical properties,migration and transformation,distribution and sources of mercury.2.The Hani peatland in Northeast China is chosen as the study area.And the natural background of the study area including geology and geomorphology,climate and hydrology,vegetation and soil conditions are introduced.The Hani peat sediment is selected as the studying object.And the process of peat sample collection and pretreatment are described in detail.At the same time,the research methods and experimental process of paleoclimate and environmental substitution indicators from Hani peat are summarized and discussed in the paper.3.According to the detailed records of peat color and lithology in the sampling site of Hani peatland to set peat level control points,the AMS14 C dating technique is used to determine the age of peat samples at control points.A total of 12 peat plant cellulose 14 C age data are obtained and the 14 C age data are corrected using CALIB4.3 software.Combining with the depth and age data of peat profile,the segmented linear interpolation method is used to establish the chronological framework of Hani peat profile.The results show that the maximum depth of Hani peat profile is 9 m,the age limit of Hani peat deposition is 13937 cal.a BP(corresponding to the 14 C age of 11930±172a BP),and the peat deposition rate ranges from 0.018 cm /yr to 0.311cm/yr.4.The humification degree of Hani peat is measured using alkali extraction solution absorbance method and the 540 nm wavelength absorbance value is selected to express the degree of Hani peat humification.Meanwhile,the magnetic susceptibility of Hani peat is measured using Kappbridge MFK1-FA magnetic susceptibility meter under the conditions of low frequency magnetic susceptibility F1(976HZ)and high frequency susceptibility F3(1561HZ).By comparing with Hanni peat cellulose ?13C and ?18O climate indicators,the paleoclimate significance of Hanni peat humification degree and magnetic susceptibility indicators are discussed.It shows that the higher Hanni peat humification degree and magnetic susceptibility indicate the warmer and wetter climate,the lower Hanni peat humification degree and magnetic susceptibility indicate the colder and drier climate.5.All of the peat cellulose ?13C,?18O climate indicators,peat humification degree and magnetic susceptibility indicators from Hani peat have significant response to cold climate events including the Younger Dryas(YD)event,8.2ka BP event,4.2ka BP event and so on.The indicators show the rapid decline in temperature,the cold and dry climate simultaneously during the cold climate events period.It suggests that climate change in Hani area Northeast China during the Holocene remains relatively consistent with global climate change.At the same time,the climate and environment evolution process of Hani area Northeast China since 14.0ka BP is discussed through the multi-environment substitute indicators system,which can be divided into the following six stages: 14.0~11.5ka BP with cold climate conditions since the last deglacial;11.5~9.8ka BP with warm and humid climate conditions in the early Holocene;9.8~8.0ka BP with cold and dry rapid changes climate conditions;8.0~4.8ka BP with the suitable warm and humid climate conditions in the middle Holocene;4.8~1.8ka BP with alternating cooling and warming climate conditions;1.8~0ka BP with cold and dry climate conditions in late Holocene.6.Using the aqua regia water bath digestion method to process the peat sample,and mercury content of the peat digestion solution is tested with the AFS-8230 Atomic Fluorescence Spectrometer.It shows that the mercury content in Hani peat ranges from 1.6ng/g to 508.8ng/g with the average concentration of 45.133ng/g;the atmospheric mercury deposition flux of Northeast China ranges from 0.12?g.m-2.yr-1~ 1.6ng/g to102.63?g.m-2.yr-1 with the average flux of 8.14?g.m-2.yr-1.The Hani peat has completely recorded the atmospheric mercury deposition history of Northeast China region since the Holocene,which can be divided into the following five stages: 11.5~10.2ka BP with atmospheric mercury deposition rapid fluctuation rising stage;10.2~9.0ka BP with atmospheric mercury deposition rapidly decreasing stage;9.0~8.0ka BP with atmospheric mercury deposition violent fluctuations abnormal stage;8.0~2.0ka BP with atmospheric mercury deposition alternately fluctuates stable decreasing stage;2.0~0ka BP with atmospheric mercury deposition fluctuates rapidly rising stage.7.The atmospheric mercury deposition of Northeast China recorded by Hani peat has good response to cold climate events including YD event,11.1ka BP event,10.3ka BP event,8.2ka BP event,4.2ka BP event and the Little Ice Age event,it shows that atmospheric mercury deposition content and flux both reach to very high peak values simultaneously during the cold climate events period.The comparative study of the Holocene climate change and atmospheric mercury deposition in the northeastern region shows that the atmospheric mercury deposition is significantly enhanced during the cold and dry climate conditions,the atmospheric mercury deposition is relatively weakened during the warm and humid climate conditions.It suggests that the cold and dry climate is conducive to promote the atmospheric mercury deposition of Northeast China region,and vice versa.8.The acidification method is used to extract the volcanic ash layer from Hani peat.And the morphology and chemical composition of volcanic ash are studied using polarizing microscope,environmental scanning electron microscope and electron probe test technical means.In combination with the age of volcanic ash layer,it can infer that the volcanic ashes come from the eruption of the Tianchi volcano in Changbai Mountain during 8352 ± 76 a BP~9604 ± 80 a BP(AMS14C age)corresponding to the corrected age of 9337 a BP ~10745a BP.At the same time,it is found that the atmospheric mercury deposition of northeastern region has significant response to the volcanic eruptions of Northeast China and East Asia regions in the Holocene.During the strong volcanic eruption periods,the atmospheric mercury deposition content and flux recorded by Hani peat both stay in high level or reach to the peak values.It indicates that the strong volcanic eruptions can cause regional or global atmospheric mercury rising sharply in a short time and result in local or large-scale atmospheric mercury deposition increased rapidly.9.The internal mechanism of atmospheric mercury deposition respond to Holocene climate change in Northeast China may be interpreted as: In the centuries or millennial scale,the cold and dry climate would reduce the activity of gaseous elemental mercury(Hg0)in the atmosphere which lead to the Hg0 a fast deposition speed under condensation.Then plants in Hani peatland can accept the supply of gaseous elemental mercury from global scale,the atmospheric mercury deposition content and flux recorded by Hani peat are enhanced as a consequence.During the warm and humid climate period,the deposition speed of gaseous elemental mercury slows down resulting from the increased activity,Hani peatland mainly accepts the supply of particle mercury,mercuric chloride and a small amount of gaseous elemental mercury,the total amount of atmospheric mercury deposition is relatively decreased.The internal mechanism of atmospheric mercury deposition respond to volcanic eruptions in Northeast China may be interpreted as: A number of intense volcanic activities have erupted in Northeast China and East Asia during the Holocene,the atmospheric mercury content has increased sharply during volcanic eruption periods which also promoted the atmospheric mercury deposition.At the same time,the acid gases from volcanic eruptions such as HCl,H2 S,etc.can cause the pH of atmospheric mercury droplets decreasing,resulting in atmospheric mercury deposition increased.On the other hand,large-scale volcanic eruption will lead to rapid cooling,and bring in the colder and drier climate conditions which promote the atmospheric mercury deposition of Northeast China.Volcanic eruptions will enhance the atmospheric mercury deposition through improving both the total amount of atmospheric mercury and the rate of deposition.Therefore,the significant increasing in atmospheric mercury deposition responses can always be found during the strong volcanic eruption periods in Northeast China and East Asia. |
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