Lake Level And Water Volume Reconstruction Of Dali Lake And Its Implications

Monsoon system as an important component of modern climate system,which controls precipitation over mainland in global scale.The onset,variability and future change of monsoon have been widely investigated using various methods,such as sediments,landscape site,physical and chemic proxies,meanwhile the reconstruction of monsoon climate from qualitative to quantitative.Although huge amount of information have been summarized to catch the signal of monsoon climate change,such as loess,speleothem,lake sediment et al.,but the reconstructed results do not always consistent with each other.For example,speleothem record suggest that the strongest EAM during early Holocene,while the study of loess show that the strongest EAM during the middle Holocene.Whether this inconsistence coursed by the diachronism of monsoon or the multi-explanation of proxies is still under debate.A proxy which could accurately describe the pattern of monsoon dynamic is in urgent,luckily,we find an effective record.The change of monsoon intensity lead to change of precipitation especially in the monsoon margin region.The closed lake could consider as a natural rain gauge,and the beach ridges could be consider as natural scale.Multiple beach ridges could be used to reconstruct paleo-lake level,water volume,and estimate the change of monsoon precipitation.The Hunshandake sandy land located in the margin of East Asia Summer Monsoon(EASM),which sensitive to monsoon precipitation.Our study site Dali Lake is situated in the north of the Hunshandake sandy land in North China.We investigate 13 beach ridges of different altitude and obtained 16 Optically Stimulated Luminescence(OSL)samples.Based on this data,and using the model of ArcGis 10.1,along with 1:25000 DEM data,we reconstructed a temporal sequence of water level and water volume since the last deglaciation,in North China.Through the analysis,we conclude that the origin of water mainly from summer monsoon precipitation and brought into the lake by river or underground water.Hence,the water volume of lake directly record the precipitation brought by East Asian summer monsoon.We using the dynamic of water volume of Dali Lake to qualitative reconstructed the strength of East Asian summer monsoon.The climate restored during the early Holocene(13.0-7.7 ka),with the increase of water level from 1256 m to 1269 m,and water volume from 16.69 km3 to 28.46 km3.The water level and water volume largely decreased during 9.3-7.7 ka with the decreasing of water level to 1262 m,and the decreasing of water volume to 21.72 km3.This suggest the monsoon have already dominated this area with amount of precipitation.The water level of Dali lake largely increased during middle Holocene(1.1-5.2 ka)from 1226 m to 1282 m,meanwhile water volume reach its maximum of 43.33 km3 at 5.8 ka,which is 20 times larger than modern water volume.This data indicate that the summer monsoon strengthened,and reach its maximum value.The water level and water volume of Dali Lake drop to 1249 m and 11.79 km3 during 5.2-4.1 ka,and decreased to modern level of 1226 m and 1.96 km3 since 4.1 ka,and still shrinking suggest weaken of monsoon precipitation since late Holocene.The reconstructed paleo-water level and water volume suggest that EASM was strong during early Holocene,reach its maximum level at middle Holocene and decreased later which consist with the result that monsoon precipitation was the strongest during middle Holocene.In order to explore the driven of monsoon changes,we compare the result of monsoon precipitation with other proxies such as summer insolation of 43°N,sea level,pCO2,based on accurate age of beach ridges.We found that the dynamic of global ice volume consist with early to middle Holocene increase of monsoon precipitation while less fit after,and the Middle to late Holocene decrease of monsoon precipitation consist with the change of summer insolation of 43°N.Hence,we suggest the monsoon precipitation in this region mainly control by water sea level/global ice volume,and the insolation of high latitude also contribute.