太湖梅堰孔沉积记录揭示的全新世以来环境演变^*

Environment evolution since the Holocene revealed by lacustrine sediments of Meiyan borehole in Taihu Lake,eastern China

摘要

以太湖东南岸梅堰孔湖相沉积岩心为研究对象,在AMS ¹⁴C测年数据建立可靠年代序列的基础上,利用元素地球化学指标重建太湖地区全新世以来气候变化,并进行盐度与有孔虫分析以探究太湖东南岸是否受到海侵影响。结果表明: 11—9.1 cal.ka BP太湖地区气候由湿润逐渐转向干旱; 9.1—6.1 cal.ka BP气候整体湿润,其中8.8—7.1 cal.ka BP阶段是最湿润时期; 6.1—2.0 cal.ka BP降水最少,气候偏干; 2.0—0 cal.ka BP降水逐渐增多,气候湿润。整个全新世阶段太湖东南岸受海侵影响的可能性较低。区域对比结果表明,中晚全新世太湖流域沉积记录与邻近地区其他研究结果具有较高的相似性,具体表现为中全新世气候趋于干旱,2.0 cal.ka BP以来气候湿润。进一步将太湖流域环境代用指标与太阳辐射和厄尔尼诺频次记录综合分析,发现研究区气候受控于太阳辐射和厄尔尼诺频次变化,且二者存在不同的主导和耦合阶段。太阳辐射通过直接和间接作用影响着太湖地区早中全新世气候,2.0 cal.ka BP以来气候呈现厄尔尼诺态,厄尔尼诺频次增强平衡了太阳辐射减弱对季风区降水的影响,成为太湖地区气候的主控因子。

Abstract

In this study,we investigate the Meiyan borehole located on the southeastern shore of Taihu Lake. Based on a reliable chronological sequence established by AMS¹⁴C dating,we use elemental geochemistry,including Rb and Sr concentrations and the Rb/Sr ratio,to reconstruct Holocene climate changes. Additionally,foraminifera analysis is employed to explore whether the Taihu Lake region was affected by transgressions. The results show that from 11.0-9.1 cal. ka BP,the climate of Taihu Lake Basin gradually changed from humid to dry;from 9.1-6.1 cal. ka BP,the general climate was generally humid,with the wettest period occurring during 8.8-7.1 cal. ka BP;from 6.1~2.0 cal. ka BP,the climate was generally dry with the lowest precipitation;from 2.0-0 cal. ka BP,the precipitation gradually increased and the climate was humid. During the whole Holocene period,the eastern area of Taihu Lake was unlikely to have been influenced by transgressions. Regional comparisons show that the Rb/Sr record in Taihu Lake are consistent with environmental proxies record in neighboring regions during the middle and late Holocene,which is characterized by gradually drying climate in the Middle Holocene and wet climate since 2.0 cal. ka BP. To further explore the climate dynamics,we compared the environmental proxy index with the 30° solar radiation in the northern hemisphere,ENSO frequency records and Holocene mean sea level records. We found that the climate of Taihu Lake Basin was controlled by the solar radiation and ENSO changes,with distinct phases of dominance and coupling between the two factors. Solar radiation affected the early and middle Holocene climate of Taihu Lake Basin through direct and indirect effects. Since 2.0 cal. ka BP,the climate has exhibited an El Niño-like state,with an intensified ENSO frequency balancing the effects of weakened solar radiation on precipitation in the monsoon region. As a result,ENSO frequency became the main controlling factor of the climate in the Taihu Lake Basin. The results will provide a reliable basis for understanding the relationship between monsoon and climate change in the lower reaches of the Yangtze River since the Holocene.

关键词

太湖 / 全新世 / Rb/Sr / 气候变化 / 太阳辐射 / 厄尔尼诺

Key words

Taihu Lake / Holocene / Rb/Sr indexes / climate change / solar radiation / El Niño

基金资助

*国家自然科学基金项目(编号: 42271173,41771221)和安徽省“十四五”规划重点项目(编号: 2022BFAFZ01365)联合资助