东北印度洋源汇过程及古环境与古季风演化

东北印度洋地理位置独特,其沉积物记录了青藏高原隆升及孟加拉扇的“源-汇”过程、印度季风与东亚季风的“海-气”交互作用、印-太暖池热传输的演变与高纬气候之间的相位关系等关键信息,是喜马拉雅地区“构造-气候-沉积”耦合演化的良好记录载体,是探讨多圈层相互作用、探索古气候与古环境演化的理想“窗口”。本文系统总结了近年来有关东北印度洋季风与表层环流特征、沉积物组成及物源、气候环境演化以及环境磁学记录等方面的研究进展。分析表明,东北印度洋为典型的季风风场,表层环流受季风影响强烈,夏季和冬季环流差异明显。沉积物类型丰富,包括河流输运而来的陆源碎屑、钙质和硅质为主的生物沉积以及火山物质等。但目前对于该区域的沉积物的具体组成、“源-汇”过程、迁移历史、季风演化与青藏高原隆升、高纬气候变化之间相互关系等方面的认识尚存在较大的分歧。同时,受样品获取难度大、磁学信号稀释严重等因素的限制,环境磁学作为一种在示踪沉积物物质来源、恢复古气候和古环境等方面被普遍认可的技术手段,在东北印度洋区并没有得到充分的发挥与应用。因此,未来需要在前人研究的基础上,将目光向东北印度洋更南、更深处延伸,对其“源-汇”过程进行全面分析。在研究方法上进一步拓展,采用更高精度的技术手段提取磁学信号,加大环境磁学的应用,寻找有效的替代性指标,解决该地区季风演化、古海洋环境变化等气候环境问题,为该地区环境气候研究提供新认识。并尝试开展地磁场长期变化(paleosecular variation, PSV)研究,建立东北印度洋的PSV记录,辅助修正全球地磁场模型,探究地球深部动力过程。

Source-sink processes,paleoenvironment and paleomonsoon evolution in the Northeast Indian Ocean

The Northeast Indian Ocean (NIO) sits at a unique geographical location, where marine sediments record the source-sink processes in the Tibetan Plateau-Bengal fan, the sea-air interaction during the Indian and Asian monsoon season, and the phase relationship between the evolution of heat transfer in the Indian Pacific Warm Pool and the high-latitude climate. It records as well the climate-tectonics-sedimentation (CTS) coupling evolution in the Himalayas, and is an ideal window to study multi-sphere interactions and explore paleoclimate and paleoenvironmental changes. This paper summarizes a series of research advances in recent years on the characteristics of monsoon and surface circulation, sediment composition and provenance, climate and environmental changes, and magnetic records of the NIO. The analysis shows that the NIO is a typical monsoon wind field where the surface circulation is strongly influenced by monsoons and obviously different between summer and winter. The sediment includes terrigenous detritus zircon ransported by rivers, calcareous and siliceous biodeposits and volcanic materials. However, there are still disagreements over the regional sediment composition, source-sink processes, migration history, monsoon evolution as well as the relationship between the Tibetan Plateau uplift and high-latitude climate change in the NIO. In addition, limited by sampling issues and weak magnetic signal, environmental magnetism, a widely accepted method for sediment source tracing and paleoclimate and paleoenvironmental restoration, has not been fully developed and applied in the NIO. Therefore, it is necessary to extend research focus further south and deeper into the NIO region and conduct a comprehensive analysis of its source-sink processes in the future. In order to solve the regional climate and environmental problems such as monsoon evolution and paleomarine environmental change, and advance local environmental and climate research, method developments are needed, which include improving high precision techniques to extract magnetic signals, and finding effective proxy indicators to increase application of environmental magnetism. Also, it is very important to establish high-resolution paleosecular variation (PSV) records for revising the global geomagnetic field model and exploring the deep dynamic process of the Earth in the NIO.