| The grain size of lake sediments is an important indicator for the reconstruction of past environments and climate change.The distribution characteristics of the grain size of lake sediments were determined by transport ways and media.Therefore,the grain size components can be used as proxies to reconstruct lake sedimentary environment and climate change.In this study,the Holocene lake sediments of the crater lakes of Huitengxile plateau(HTL2)and the inland terminal lake on the north of Siziwang Banner(HH)in Inner Mongolia have been explored.Based on the reliable AMS14C dates,this paper reconstructs the Holocene environment and climate change of the two lakes by using the research result that the spatial distribution of the grain size and the influencing factors of the lake surface sediments in-the Inner Mongolia plateau.The main conclusions are as follows:The climate change of the Holocene on Huhenaoer has gone through t'hree stages:1)9820?6800 cal.yr BP,the median size of the lake sediments is low,and the component of fines(C1:0.4?1.9?m)in the particle size is the peak,reflecting the lake sedimentary environment,and the core was located farther away from the rivers.The lake area was larger and the precipitation was higher,humid climate;2)During 6800?5200 cal.yr BP,the particle size of the sediment became coarse,and the fine component C1 and C2(2.0?12?m)almost disappeared,the coarse components C3(12?58?m)and C4(70?150?m)was increased,reflecting the core position was very close to the estuary,the lake was near dried and precipitation greatly reduced,the climate was extremely dried;3)since 5200 cal.yr BP,the particle size fluctuated significantly,the clay were generally at a low level,the coarse particles were maintained at a high level,and the depositional environment fluctuated frequently.Therefore,the lake water level was low and often dried,the precipitation was low,the climate was generally drought,of which 5200?3700 cal.yr BP,2500-1800 cal.yr BP,900-600 cal.yr BP climate was somewhat wet.The Holocene climatic and environmental changes of the Huitengliang area have gone through four stages:1)During 12,130-11,270 cal.yr BP,sand with gravel dominated and the grain size is mainly consists of coarse grain size components C3,C4,C5 and C6,showing that the sedimentary environment of the sample site was alluvial sediments.The lake had not yet developed and the climate was extremely dry;2)11,270?7880 cal.yr BP,clayey silt dominated and the mean size is at the lowest level of the whole profile,the grain size components is mainly fine particles(C1 and C2)with coarse(C4 and C5)components accompanying,reflecting the depositional environment of the lake was lacustrine sediment.The precipitation was high and the climate was humid;3)during 7880?5600 cal.yr BP,the sedimentary facies transformed into peat,indicating that the lake evolved into swamps.The peaks of the coarse C5 and C6 components also proved that the lake was nearly dried up or developed swamp,and the debris on the slope was directly reaching the center of the lake basin.Precipitation reduced and climate was somewhat dry;4)5600?3240 cal.yr BP,the sedimentary facies were still peat,and the swamp were grown at the sample site.The reductions of the C4,C5 and C6 grain size indicated that the marsh area was large,the coarse-grained sediments were difficult to reach the center location of the lake,the sedimentary facies of the lake were mainly aeolian sediments and plant peat deposition,precipitation may increase,the climate slightly moist;3240 cal.Yr BP so far,peat deposition into lacustrine sediments,the components of fine particle size(C1 and C2)increased,C3 and C4 components decreased,indicating that the swamp evolved into lakes,reflecting the increase of precipitation,climate becomes wet.Although the hydrological characteristics and the depositional environment of the Huitengliang lake(HTL2)and the Huhenaoer(HH)lakes are different,the hydrological environment and climate change reconstruction of Holocene lakes are based on a unified basis.The fines(0.4?1.9?m and 2.0?12.0?m)components reflects the lake area,the coarse particle components(greater than 70?m)changes reflecte the distance from the estuary and indirectly indicate the lake area,medium-to-coarse silt(13?58?m)may reflect the eolian deposition flux,and then indicates the changes of depositional environmentIt has a good consistency that the reconstruction of the Holocene climate change by HTL2 Lake and HH Lake particle size sequence,both of which show that the early Holocene is wet and the Mid-Holocene is arid and late Holocene are slightly moist.However,there are some differences in the sequence of climate change between the two lakes,and the time of formation and drying of HTL2 lakes in Huitengxile plateau is significantly earlier than that of Huhenaoer(HH),which may be attributed to the smaller area of the lake and watershed of HTL2,sensitive to climate change response.The reconstructed results of the Holocene climate change by the HTL2 lake and the HH lake particle size sequence show that the most prosperous period of the East Asian summer monsoon was the early Holocene,and the mid-late Holocene summer monsoon began to decline,and the change pattern of the summer monsoon closely with the summer solar radiation changes at low latitudes of the northern hemisphere may indicate that the summer solar radiation is the driving factor of the East Asian summer monsoon,and the difference of sea-land heat is the key factor of summer monsoon... |
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