末次盛冰期以来青藏高原-孟加拉湾“源-汇”系统研究进展

Research progress of the Tibetan Plateau - Bay of Bengal “source-sink” system since the Last Glacial Maximum

  • 摘要: 近20年来,国际上对末次盛冰期以来青藏高原-孟加拉湾“源-汇”系统的研究取得了重要进展。为及时跟踪研究前沿,并进一步为地球系统科学思想指导下东北印度洋源汇过程研究提供新思路,本文按照从源到汇的思路,从流域风化侵蚀、海洋沉积物来源、沉积模式、源汇系统响应等几个方面总结了目前国内外最新研究进展,并指出了未来的主要突破方向。概括起来,主要取得如下认识:恒河-布拉马普特拉河流域尺度的物理侵蚀过程主要受控于季风气候变化,而化学风化过程与季风气候关系复杂,温度、降水、植被和冰川等因子在特定时期均可能起着重要的控制作用。孟加拉湾沉积物主要来自周边河流输入的流域风化产物,以恒河-布拉马普特拉河输入的青藏高原物质为主,同时也有部分来自印度半岛和缅甸的物质;末次盛冰期以来青藏高原源区物质贡献占据绝对优势(>70%),且整体变化不大,但各物源端元贡献比例在千年尺度上出现明显波动变化。孟加拉湾陆架发育典型的风暴控制型三角洲-陆架沉积,而底层浊流和表层环流作为孟加拉湾最重要的两个输运动力,对孟加拉湾深海扇沉积物组成和分布起着重要的控制作用。总体看来,末次盛冰期以来青藏高原-孟加拉湾“源-汇”系统演化主要受印度夏季风和海平面变化控制。未来的研究应以地球系统科学思想为指导,加强海陆结合的现代沉积过程的长期连续观测,聚焦沉积记录中环境替代指标的精确解译,揭示流域风化过程对季风气候变化的响应机制;结合数值模拟和海洋大数据分析,预测快速全球变化背景下青藏高原-孟加拉湾“源-汇”系统的演化趋势及环境效应,同时加强与世界大陆边缘其他典型源汇系统的比较研究。

     

    Abstract: In the last two decades, significant approach has been made in the study on the Tibetan Plateau (TP) - Bay of Bengal (BoB) “source-sink” system since the Last Glacial Maximum (LGM). To track the research frontiers and provide new ideas on the source-sink process of the Northeast Indian Ocean under the guidance of the thought of the earth system science, we summarized the latest progress in several aspects such as weathering and erosion, sediment provenance, sedimentary patterns, and source-sink system responses, and pointed out the breakthrough directions in the future. The physical erosion process in the Ganges-Brahmaputra (G-B) basin is primarily influenced by monsoon climate change, while the chemical weathering process exhibits a complex relationship with the monsoon climate. Temperature, precipitation, vegetation, and glaciers may all play significant roles in controlling these processes in specific times. The sediments in the BoB are mostly weathered products transported by surrounding rivers, particularly from the Ganges-Brahmaputra (G-B) River that transports great amounts of materials from the TP, and partially from Myanmar and Indian Peninsula. The TP has consistently contributed >70% terrigenous materials to the BoB with little changes since the LGM. However, contributions from each provenance varied significantly on a millennial scale. The BoB shelf developed typical storm-controlled delta-shelf deposits. As two most-significant regional transport driving forces, the bottom turbidity current and surface circulation had a crucial impact on the composition and distribution of deep-sea fan sediments. In general, the evolution of the TP - BoB “source-sink” system since the LGM is mainly controlled by the Indian Summer Monsoon (ISM) and sea level changes. In the future, more attention shall be paid to develop the joint land-sea long-term observation of modern deposition processes, and focus on the accurate interpretation of environmental signals in sedimentary records and response mechanism of weathering processes to monsoon climate change. With numerical simulation technology and marine big data, the evolution and environmental impacts of TP - BoB “source-sink” system under the fast global changes deserve more investigations. Meanwhile, comparative studies on other typical source-sink systems in the continental margins of the world shall be strengthened.

     

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