升金湖沉积物1000年以来的元素地球化学记录及其水文意义

中国东部季风区过去千年的水文变化已有大量研究并取得重要进展,但水文环境变化的起止时间、空间特征、温湿配置研究仍存在显著的区域差异,水文环境变化的驱动机制研究相对较少且不明确。以安徽升金湖沉积岩心为研究对象,分析元素地球化学指标的水文指示意义,结合总有机碳(TOC)、碳氮比(C/N)、无机碳(IC)等环境代用指标,讨论升金湖过去1 000年的水文变化。结果表明:1)在1 000～1 350 A.D.,Ti、Rb/Sr、Cr、SiO₂含量呈波动下降,Sr、CaO含量呈低值波动,指示中世纪暖期水文环境向干旱化变化。2)在1 350～1 850 A.D.内可分为两个阶段;第一阶段(1 350～1 600 A.D.),Ti、Rb/Sr、Cr、SiO₂含量波动变化,但总体在高值水平,Sr、CaO含量为低值,指示流域降水较多;第二阶段(1 600～1 850 A.D.),Ti、Rb/Sr、Cr、SiO₂含量下降,总体呈低值水平,Sr、CaO含量为高值呈上升趋势,指示降水减少,说明小冰期水文环境由湿润转向干旱。3)1 850～2 000...

Geochemical Element Records and Hydrological Significance of Lake Shengjin Sediments During the Past Millennium

The hydrological changes in the monsoon region of eastern China over the past thousand years have been extensively studied and substantial progress has been made. However, there are significant apparent regional differences between the time interval, spatial characteristics and the combination of temperature and humidity. The driving mechanisms of humidity changes in the monsoon region of eastern China are also still unclear. To better understand the hydrological variations and internal and external mechanisms in the region over the past thousand years, it is necessary to continue to strengthen the reconstruction and driving mechanism of high-resolution hydrological changes. Lake Shengjin （30°15'?30°28' N, 116°58'?117°14' E） is located in Chizhou city, Anhui province, on the southern bank of the Yangtze River and covers an area of 133 km2. The lake consists of upper, middle and lower lakes. The climate of the lake basin is subtropical monsoonal, with an annual average temperature of 16.1 °C and an annual average precipitation of 1 600 mm.The 86 cm long sediment core SJPC19-3 was drilled in the shallow wetland area of the lake in March, 2019. The sampling site is located at 30°20' N, 117°00' E. The core was divided into intervals of 0.5 cm between 9 and 30 cm and intervals of 1 cm between 30 cm and 86 cm. The hydrological significance of geochemical elements was analyzed from reliable accelerator mass spectrometer （AMS） 14C isotope data. The paleohydrological changes in Lake Shengjin during the past millennium were reconstructed from geochemical elements and combined with total organic carbon （TOC）, carbon-nitrogen ratio （C/N）, inorganic carbon （IC） and other environmental proxies. The changes were divided into three stages: （1） In Period I （1 000?1 350 A.D.）, corresponding to the Medieval Warm Period （MWP）, Ti, Rb/Sr, Cr and SiO₂ content gradually decreased, and Sr and CaO content fluctuated at low values, indicating general aridification of the lake basin during the MWP. （2） Period II （1 350?1 850 A.D.）, corresponding to the Little Ice Age （LIA）, was divided into two substages: （2A） From 1 350 A.D. to 1 600 A.D. （early LIA）, Ti, Rb/Sr, Cr and SiO₂ fluctuated at a high level, and Sr and CaO content remained low, probably reflecting more precipitation in the basin. （2B） From 1 600 A.D. to 1 850 A.D. （i.e., the later LIA）, Ti, Rb/Sr, Cr, SiO₂ content decreased and the overall trend was low, whereas Sr and CaO content was high and increasing, indicating less precipitation and a drier environment. （3） In Period III （1 850?2 000 A.D.）, corresponding to the modern warm period （MWP）, Ti, Rb/Sr, Cr and SiO₂ content was increasing and Sr and CaO decreased, indicating high precipitation and humid conditions in the lake basin. It is notable that the hydrological changes reconstructed in this study correspond closely with historical documents for the period from 1 137 A.D. to 1 993 A.D. A comparison with other reported regional reconstruction results indicates that these hydrological changes in Lake Shengjin are consistent with the environmental changes for Lake Daijiu and Nüshan, and for Dajiu peat. To further understand the driving mechanisms of the hydrological variations in Lake Shengjin, the results of this study were compared with trends of the Asia-Pacific oscillation （APO） and northern hemisphere solar irradiance change. Their close consistency suggests that the hydrology of Lake Shengjin during the past millennium may have been mainly driven by changes in the APO and solar radiation in the northern hemisphere.