长江口及邻近海域是我国近海低氧现象发生最突出的海域，低氧现象频发对海洋生态安全与国民经济发展构成了严重威胁。该海域同时受到长江径流与黑潮输入的双重影响。近年来逐渐有研究指出，黑潮近岸分支(NKBC)入侵对低氧区形成具有重要影响，NKBC入侵水体的生物地球化学耗氧过程可能是影响低氧区的重要原因之一。此外，NKBC对长江口典型海域的入侵存在显著的时空变化。然而目前对于NKBC入侵水体关键耗氧过程的时空变化及其对DO消耗的影响缺乏深入了解，NKBC入侵对低氧现象的贡献缺乏定量化研究。本项目拟围绕低氧现象“孕育-发展-形成-消失”各主要阶段，辨析NKBC入侵长江口典型海域的时空变化，揭示入侵水团关键耗氧过程及其时空变化对DO的影响，定量化评估NKBC入侵对低氧区的贡献。研究结果有助于深入揭示人类活动和大洋入侵双重影响下低氧区的时空变化规律与成因，并为低氧生态灾害的预测、防控提供科学依据和技术支撑。

Hypoxia off the Changjiang estuary (CE) and its adjacent waters is most prominent in the coastal waters of China. The frequent occurrence of hypoxia poses a serious threat to marine ecological security and national economic development. The hydrodynamics of CE and its adjacent waters is complex, which is affected by the Changjiang diluted water (CDW) and the near-shore Kuroshio branch current (NKBC). Recent studies have suggested that the invasion of NKBC played an important role on the formation of hypoxia in this area. And during the NKBC invasion, the biogeochemical processes which consume oxygen may be one of the important reasons influencing the hypoxia. In addition, there are significant seasonal variations in the NKBC invasion, which may be an important factor triggering the generation and dissipation of hypoxia. However, there is a lack of in-depth understanding of the spatiotemporal variations in the biogeochemical processes during the NKBC invasion. In addition, there is a lack of quantitative research on the contribution of NKBC invasion to the hypoxia in the target area. Therefore, by combining voyage investigations, field experiments and numerical simulations, this project intends to reveal the spatiotemporal variations in the range and intensity of NKBC invasion, elucidate the key oxygen consumption biogeochemical process and its spatiotemporal variations during NKBC invasion, and quantitatively explore the contribution of NKBC invasion to the evolution of hypoxia. The results could reveal the spatiotemporal variations and its causes of hypoxia under the dual pressures of human activities and ocean invasion, and provide scientific basis and technical support for the prediction, prevention and control of hypoxia disaster.