Climate And Environment Changes In Huguang Maar Lake During The Little Ice Age

Huguangyan Maar Lake is located in the southernmost of China,it’s strongly influenced by monsoon climate.Meanwhile,as a standard Maar Lake,it provides a large amount of continuous information of the paleoclimate and paleoenvironment has attracted extensive attention of scientist.In the past,there had been a lot of reports about the East Asian summer monsoon and the dry/wet variation.However,due to lack of reliable proxies,East Asian winter monsoon were rarely reported.Also,scientist pay more attention in long time scales of climate change.Due to the limitation of time resolution,few studies reported the climate variation during the Little Ice Age,especially in South China.In some way,it limits our understanding of the temporal and spatial characteristics of the East Asian monsoon during the Little Ice Age.In this study,a 100 cm long sedimentary core HGY19 is collected in Huguangyan Maar Lake.The age model is established based on the ²¹⁰Pb at the top and the AMS ¹⁴C age in the core and the magnetic susceptibility comparison.The magnetic susceptibility and TOC content in lake sediments are selected as indicators of summer monsoon precipitation changes,δ¹⁵N_organdδ¹⁵N_TNare used as indicators of the change of East Asian winter monsoon intensity.The variation characteristics and possible driving mechanisms of East Asian summer monsoon and East Asian winter monsoon within the Little Ice Age were discussed.In the early Little Ice Age（1450～1550AD）,more precipitation and more humid climate was recorded in the core HGY19.In the late Little Ice Age（1450～1550AD）,the precipitation decreased and the climate was drier.This is consistent with the dry/wet change reconstructed by other proxies for Huguangyan Maar Lake and it is consistent with the precipitation records in other areas in southern China but it shows an opposite change with the precipitation records in northern China.Pacific Decadal Oscillation（PDO）variations may be responsible for the spatial variability of climate change within the Little Ice Age.In the early Little Ice Age,PDO was in warm stage,which resulted in increased rainfall in the south and decreased rainfall in the north.In the late Lite Ice Age,PDO turned in the cold period,resulting in less precipitation in southern China and more precipitation in the northern China.δ¹⁵N_organdδ¹⁵N_TNare good proxies of the East Asian winter monsoon to reconstruct the history of the East Asian winter monsoon during the Little Ice Age.We suspect that the strong winter monsoon enhances the vertical mixing of lakes,which not only leads to the increase of primary productivity,but also inhibits the deposition of algae and promotes the decomposition of dead algae in the water.And the decomposition may be stronger than the primary productivity of the lake.Therefore,the heavierδ¹⁵N_orgindicates the strengthening of the East Asian winter monsoon,while the lighterδ¹⁵N_orgindicates the weakening of the East Asian winter monsoon.The East Asian winter monsoon is weak in the early Little Ice Age and stronger in the late Little Ice Age,which is consistent with the other reports.The variation of the East Asian winter monsoon during the Little Ice period may be mainly influenced by the Arctic Oscillation（AO）.When the AO is in positive phase,the East Asian winter monsoon is weak,when the AO is in negative phase,the East Asian winter monsoon is strong.