中国中部高山湖泊记录的小冰期水热配置不同模态

Different modes of hydrothermal configuration recorded in alpine lakes of central China during the Little Ice Age

小冰期水热配置模态在中国南北方存在明显差异,敏感响应于气候变化的高山湖泊在小冰期阶段水热变化模式仍缺乏研究。选取中国中部两个高山湖泊——太白山玉皇池与六盘山东海子的沉积物岩心为研究对象,基于总有机碳(TOC)、总有机氮(TN),碳氮比(C/N)等地球化学指标,并结合已发表的水文数据,重建了东海子和玉皇池近2 ka来的水热变化模态。结果显示:近2 ka气候变化主要受太阳辐射影响,在900 AD之前,两个湖泊区域气候同为冷湿,中世纪暖期(900—1300 AD)转为暖干;在小冰期(1300—1800 AD)时期水热组合不同,东海子降水与温度呈同步下降趋势,主要受控于东亚夏季风,而处于东海子东南方向的玉皇池表现为降水的持续增加,可能受加强的印度季风和厄尔尼诺-南方涛动(ENSO)的共同影响。

Background,aim,and scope The Little Ice Age is a typical climatic event in the last 2 ka,and its hydrothermal configuration patterns differ markedly between southern and northern China.There is still a lack of research in the modes of hydrothermal change in alpine lakes that sensitive to climate change during the Little Ice Age and different geographical lakes about the hydrothermal configuration modes remain poorly understood.Based on the study of the climate change process of two alpine lakes in different geographical locations over the past 2 ka,this paper discusses the similarities and differences of the hydrothermal configuration modes and the possible driving mechanism during the Little Ice Age.Materials and methods In this study,sediment cores from two alpine lakes in central China,Yuhuangchi in the Taibai Mountain and Donghaizi in the Liupan Mountain were selected.By comparing index of the total organic carbon(TOC),total organic nitrogen(TN),carbon and nitrogen ratio(C/N)with published temperature and hydrological records in the area,we discussed the reliability of TOC and TN for indicating temperature variation,and reconstructed the hydrothermal patterns of Donghaizi and Yuhuangchi over the last 2 ka.Results The climate change during the last 2 ka were mainly influenced by total solar radiation,with the climate of both lakes being cold and wet until 900 AD,and turning warm and dry during the Medieval Warm Period(900—1300 AD);the hydrothermal combination was different during the Little Ice Age(1300—1800 AD),with Donghaizi showing a synchronous decline in precipitation and temperature,while Yuhuangchi,which is located in the southeast of Donghaizi,showing an increase in precipitation.These two alpine lakes in different geographical locations showed different modes of hydrothermal configuration during the Little Ice Age.Discussion The decreased trend of Donghaizi precipitation during the Little Ice Age is consistent with the precipitation changes reconstructed by pollen in the north China,indicating it is mainly controlled by the East Asian Summer Monsoon and the hydrothermal configuration changes synchronically.However,precipitation at Yuhuangchi,located at south of Donghaizi,showing an upward trend during this period,suggesting that it was controlled by a more complex driving mechanism.The East Pacific sea surface temperature(SST)record shows an El Niño state during this period,coupled with the extension of the West Pacific Subtropical High to the southwest,which met with the Indian monsoon in its strong phase.Therefore,they gathered in front of the Qinling Mountain and produced topographic rain as the elevation increased.In addition,they brought a large amount of clouds with increasing precipitation and producing a umbrella effect that made the Yuhuangchi area cooler.Conclusions The variation of TOC and TN in sediments from Donghaizi and Yuhuangchi correspond to the variation of area temperature.Before the Medieval Warm Period,the climate of the two lakes changed synchronously.However,during the Little Ice Age,the precipitation and temperature in Donghaizi decreased synchronously,which was mainly controlled by the East Asian Summer Monsoon,while the precipitation in Yuhuangchi showed an increase in precipitation.This is probably influenced by the strengthening Indian monsoon and the El Niño-Southern Oscillation.Recommendations and perspectives The results are valuable for understanding the spatial characteristics and driving mechanism of precipitation in east Asia during the Little Ice Age.