Climatic and environmental characteristics of the Medieval Warm Period revealed by n-alkane records in the Shuangchi Maar Lake,Hainan Island
With a focus on the Medieval Warm Period(MWP)and the Little Ice Age(LIA),the last millenni-um is a crucial period in the study of global climate change.In this study,a sediment core(SCH17-04)was col-lected from Shuangchi Maar Lake,Hainan Island,South China,and its n-alkanes proxies,including the ratios of Tree/Grass,Proportion of aquatic(Paq),Carbon Preference Index(CPI)and Average Chain Length(ACL)were determined.Based on the analysis of Accelerator Mass Spectrometry(AMS)14C age and n-alkanes,the climatic and environmental characteristics of this region were reconstructed from 775 to 1550.The results showed that the proportion of long-chain n-alkanes was relatively high,while the proportion of medium-and short-chain n-alkanes was relatively low,suggesting that the organic matter inputs to the sediments of Shuang-chi Maar Lake over the last millennium were mainly dominated by terrestrial higher plants,with relatively small contributions from aquatic plants and fungi and algae.Based on the above indicators,the environmental changes of Shuangchi Maar Lake over the past millennium can be divided into three stages:1)In the late Dark Ages Cold Period,the gradual decrease in the Tree/Grass ratio and the significant increase in the ACL value in-dicated a gradual decrease in woody plants in the study area,indicating that the climatic environment of the study area was drier during this period.2)In the Medieval Warm Period,low Tree/Grass values and high ACL values indicated an increase in the proportion of herbaceous plants and a relative decrease in the proportion of woody plants in the study area,suggesting a drier climate during this period.3)In the early Little Ice Age,the increase in Tree/Grass values and decrease in ACL values indicated a gradual increase in the proportion of woody vegetation and a gradual decrease in the proportion of herbaceous vegetation,indicating a wetter cli-mate during this period.In addition,the n-alkane records of Shuangchi Maar Lake were consistent with other climate records revealed by the lacustrine sediments of Huguangyan Maar Lake in the northern Leizhou Penin-sula,Dongdao Island in the Xisha Islands,and stalagmite records from Thailand,etc.,indicating a relatively dry climate condition during the Medieval Warm Period.Furthermore,it was found that during the Medieval Warm Period(Little Ice Age),the drier(wetter)climatic characteristics of the tropical northern margin could be related to the northward(southward)migration of the Intertropical Convergence Zone,the expansion(contrac-tion)of the tropical rainbands,and the decrease(increase)of the sea surface temperature gradient in the eastern and western Pacific,respectively.
tropical regionn-alkanesMedieval Warm PeriodLittle Ice Age
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