长江口及邻近海域底层水体低氧物理机制的研究进展

人类活动和自然因素共同但有区别的作用引起了长江口及邻近海域富营养化，造成夏季底层水体低氧现象加剧，成为近海生态健康恶化的重要征兆。本文梳理了国内外学者在该海域低氧研究中获得的重要认识，分析了底层水体溶解氧的潮周期尺度、事件尺度和年际尺度的变化特征，重点从层化与物质输运角度，介绍了长江冲淡水、台湾暖流、海洋锋面、风和潮等过程影响底层水体中氧气消耗或补充的机制，揭示了本海域主要低氧现象分别位于长江口和浙江近海的特征，对比了两处低氧区形成与演变的异同机制。目前，对低氧形成机制的定性认识和多尺度变化特征的了解已经有较好的基础，未来需要从多学科交叉角度加强现场试验和定量研究，掌握低氧的长期演变趋势，研发底层水体低氧的预测预警技术，支撑我国河口近海的生态预警监测工作。

Recent progress on the studies of the physical mechanisms of hypoxia off the Changjiang (Yangtze River) Estuary

The combination of human activities and natural factors has formed the eutrophication of the Changjiang (Yangtze River) Estuary and its adjacent waters, leading to increased hypoxic condition in the bottom water in summer, which has become an important signal of the deterioration of ecosystem health. This paper combs the important understandings gained from the recent studies of hypoxia in this area, analyzes multi scale temporal changes of dissolved oxygen, e.g., focusing on the tidal scale, event scale, and inter annual scale, and factors relevant to stratification and material transport. The relevant mechanisms analyzed includes processes such as the diluted water extension, Taiwan Warm Current, fronts, wind field and tides that affect oxygen consumption or transport process. It is also revealed that the main hypoxia phenomena were separated in the Changjiang Estuary and the coastal waters of Zhejiang Province. The similarities and differences in the formation and evolution of the two hypoxic zones were presented. At present, a solid foundation has been laid for the understanding of the hypoxia occurrence, however due to its multi scale temporal variations, field experiments and quantitative studies should be strengthened from a multidisciplinary perspective, and the long term evolution trend of hypoxia in this area should also be clarified based on long term time series monitoring.