夏季长江口外东北部低盐水团频发区的生物地球化学过程及机制

The biogeochemical responses to the diluted water extension off estuaries are important scientific hotspot issues in the regional oceanographic discipline. The offshore detached low-salinity water lens (LSWL) in the northeastern area off the Changjiang estuary frequently occurs in summertime. Previously, some studies have mainly examined the physical mechanisms forming the offshore detached LSWL. However, the biogeochemical responses to the offshore detached LSWL have been short of study. This project will focus on the offshore detached LSWL in the northeastern area off the Changjiang estuary by emphasizing an interdisciplinary approach (physical-sediment transport-chemical-biological coupling). We will first investigate the chemical-hydrological and biological characteristics of the offshore detached LSWL and how it will impact the light conditions within the local diluted water. Then, the mechanisms of nutrient transport off the Changjiang estuary and adjacent areas triggered by the offshore detached LSWL will be demonstrated. Finally, the primary production processes within the offshore detached LSWL area will be studied by focusing on the phytoplankton responses to the offshore detached LSWL, and the local bottom hypoxia and carbonate system associated to the offshore detached LSWL are further explored. The outcome of this project will not only deepen our understanding on the coupling of physical, chemical and biological processes in the offshore detached LSWL off the Changjiang estuary, but also benefit a solid foundation for revealing its influence to the Yellow and East China Seas on regional scale.

河口冲淡水扩展及其生物地球化学过程响应一直是区域海洋学研究的热点问题，而孤立低盐水团是河口区独特的海洋学现象。针对夏季长江口外东北部海域的低盐水团，目前多是从物理海洋学的角度对其形成的动力学机制进行了探讨，尚缺乏对其生物地球化学过程响应及机制的研究。本项目从水文-化学-生物过程的耦合作用入手，深入分析该低盐水团的化学、水文学和生物学特征；研究低盐水团的形成对局地冲淡水光照条件的影响，揭示其对长江口及邻近海域营养盐输移的影响机制；研究低盐水团区的初级生产过程，阐明浮游植物生物量等对低盐水团的响应机制，并进一步探讨低盐水团对局地底层低氧和碳酸盐体系的影响。此项研究不仅将深化对河口外这一特定环境中物理-化学-生物过程耦合作用及机制的认识和理解，更为揭示低盐水团对河口区及其邻近海域生态系统的影响奠定基础。

河口冲淡水扩展及其生物地球化学过程响应一直是区域海洋学研究的热点问题。本项目针对夏季长江口外东北部海域的低盐水团现象，基于多学科交叉，在分析低盐水团区化学、水文学和生物学特征的基础上，深入探讨了该海域的物理-生物地球化学过程及机制。研究揭示了夏季长江口区域存在脱离冲淡水主体的离岸低盐水团现象，该海域的上升流系统是导致低盐水团与冲淡水主体相分离的重要因素。长江口外典型化学、生物要素的分布与离岸低盐水团之间具有良好的内在对应关系；低盐水团的形成可导致营养盐的离岸输运，而且较低的悬浮物含量亦使其具有较好的水体光照条件，因此可促进初级生产和浮游植物繁殖。研究指出夏季长江口外东北部离岸低盐团影响区独特的海洋环境可诱发外海赤潮，并在底层对应形成一低氧、酸化核心；同时，强烈的生物活动是该海域CO2源/汇格局的主要影响因素，并在一定程度上制约海-气界面间的CO2通量。研究还首次在夏季长江口海域同时观测到了冲淡水离岸扩展、上升流、藻华和中层低氧等现象的耦合，并发现冲淡水离岸输运所形成的低盐水外缘锋面总体控制着浮游植物高值区的外部边界，进而显著影响长江口底层低氧区的离岸侧边界。此项研究为深入理解河口海域离岸低盐水团的生物地球化学响应和生态环境效应提供了重要科学依据，并为相关过程的模拟奠定了坚实的基础。