Climate Change Since The Last Deglaciation Recorded By Lake Zigetang,Central Tibetan Plateau

Climate change since the last deglaciation and the driving mechanism is a hotspot and focus in Quaternary climatology research,which has a major impact on understanding the climate evolution rule and the rise and fall of ancient civilizations in post-glacial period,and also plays an irreplaceable role in predicting the future climate development direction and solving the contradiction of human and environment under the background of climate change.The Tibetan Plateau?TP?is unique in geographical location,terrain&landscape and atmospheric condition,has important influence on climate change in adjacent areas.A large number of lakes on the plateau have been proved to be ideal geological archives for recording of palaeoclimate information,some of which have played a pivotal role in climate reconstruction on thousand years scale.As open information receivers,lakes can preserve all kinds of information from the atmosphere,the surface of the lakes basin and the water in the lake,which,after effective extraction and scientific interpretation from lake sediments,can not only reconstruct the regional palaeo-climate,palaeo-environment and palaeo-vegetation,but also restore the hydrological information and human activitiesLake Zigetang,in central TP,was selected as the research object,which is a closed lake basin,located at the edge of the Asian monsoon?AM?region,with no modern glacier exist in the basin,simple water balance conditions,thermal and chemical stratified lake water body,and high resolution which is higher than most lakes in the Tibetan Plateau.Therefore,the lake sediment is an excellent material for the study of paleoclimate.A 12.9 m core?ZGT2?was obtained in the deepest part of the lake,and was sampled by 1 cm interval in the lab,and age model was established by 16 AMS ¹⁴C dating data.Grain size,organic matter content,carbonate content,the content of bacteriophaeophytin-a?Bph-a?and redness degree was analyzed to reconstructed climate and lake evolution since 17.3 cal ka BP.We draw the following conclusions:1.Palaeo-climate reconstruction in central Tibetan Plateau since the last deglaciationClimate was cold and dry in the late glacial period?17-15.3 cal ka BP?,and became warm or cool and wet slowly;B?lling-Aller?d?BA?warm period?15.3-13.1cal ka BP?was a warm and humid period which quickly appeared and disappeared,during which 5 relatively independent Indian summer monsoon?ISM?strengthened events were roughly the same as the warming time in the Greenland;Temperature declined rapidly but rised slowly in YD cold period?13.1-11.9 cal ka BP?,with the climate characteristics of cold and dry in the first half and cold and wet in the second half in TP.Holocene climate in TP was relatively warm and humid,and can be characterized as follows:early-Holocene?11.9-8.2 cal ka BP?was warm and wet;the middle stage?8.2-3.7 cal ka BP?was hot and dry;the late-Holocene?3.7-0 cal ka BP?climate showed a cooling trend,the precipitation has increased.In general,the Holocene climate in TP shows a pattern of warm and dry–cool and wet.2.The response of granularity,carbonate content,organic matter content in Zigetang Lake sediment on climate changeFitting diameter of the main component of sediment grain size,is mainly controlled by precipitation intensity,and is related to the hydrodynamic force of the lake basin,reached the high values in early Holocene.The content and size of the coarse-component?dust component?are affected by the spring and winter wind and surface vegetation conditions,indicating the intensity of dust activities.The model size increased significantly and the content increased gradually in the Holocene,which indicated that the frequency and intensity of strong wind in winter and spring increased rapidly,and the surface vegetation degraded step by step since 12.0 cal ka BP.The carbonate content significantly increased in the Holocene,and its variation has significant negative correlation with precipitation in the last deglaciation and the Holocene,indicating that the first factor to control the carbonate precipitation is temperature and the second one is precipitation.The content of organic matter in sediments represented the combination of water and heat,which,in the Holocene,was significantly higher than that of the last deglaciation.Otherwise,the abnormal increase of organic matter content in late Holocene may be related to the increase of erosion and human activities.3.The reconstruction of wind regime and dust activity in central since the last deglaciationDuring the last deglaciation,the central TP was controlled by westerly wind,climate in where was dry and cold throughout the year,but the wind speed was relatively small,and the dust activity was very weak.In the Holocene,This region was controlled by the ASM during the warm seasons and westerly during the cold seasons.Precipitation was much more abundant than glacial periods,however,the intensity of westerly increased significantly compared with that in the cold period,the dust storm activity was frequent and strong,and reached a peak during the late Holocene.4.The evolution history of Lake Zigetang since the last deglaciationThe Zigetang Lake water level was low,salinity was high,water body was completely mixed in the late glacial period,and weak seasonal stratification presented at the end of this period due to the relatively warm and wet climate;During the BA warm period,Zigetang lake is thermal and chemical stratified stably and the meromictic lake formed;The water level was reduced and completely mixed again due to the cold dry climate in YD cold period.During the Holocene,with the climate was warm and wet,the water level of Zigetang Lake might reached the highest value in the early Holocene since the last deglaciation,and the lake water body presented thermocline and chemocline throughout the year,Zigetang Lake evolved into meromictic lake.The thermocline and chemocline depth was mainly affected by air temperature,and the stratification intensity feature was firstly increased and then decreased,reaching the strongest in the middle Holocene.5.Analysis of climatic driving mechanism in the Tibetan Plateau since the last deglaciationClimate change since the last deglaciation in central TP is mainly affected by the drive of the three factors of solar radiation,the ice amount in northern high latitude and the India summer monsoon.At the same time,due to the particularity of the location,topography and atmosphere of the TP,its climate change has regional uniqueness.The ZGT2 core showed clear BA warm period and YD cold events,and even 5 times of warm events in the BA period can be compared with the Greenland ice core data one by one,which shows that the Tibetan Plateau climate and the northern hemisphere in high latitude areas have a strong correlation.In the early Holocene,the precipitation in the Zigetang Lake basin reached its maximum,consistented with the change pattern of the Indian summer monsoon.The temperature of the Tibetan Plateau reached the highest peak in the middle Holocene,which lags behind the peak of solar radiation?¹0.0 cal ka BP?which may be related to the precipitation in the early Holocene,which reduced the effective solar radiation and played an important role in the cooling of the earth's surface.