南黄海-长江口海域溶解氧分布和低氧、酸化特征及其控制因素

基于2019年8月与11月所获取的2个航次的水文、化学和生物资料，重点研究了夏、秋季南黄海和长江口海域溶解氧（DO）分布的时空格局及其与水文动力状况和生物地球化学过程之间的关系，探讨了该海区低氧特征及其对酸化环境的指示.结果表明，研究海域内DO含量及分布与流场/水团格局具有良好的对应关系，其中夏季长江口外台湾暖流影响区具有低氧的特征，秋季则在黄海冷水团海域下底层存在一个DO低值区.在上升流影响下，夏季长江口海域的底层低氧水体可抬升至上层水体，低氧水体由长江口海域向东北方向扩展；夏季长江口外下层低氧水体的涌升、黄海冷水团区DO最大值层的抬升均与跃层的抬升趋势基本一致，不仅反应了上升流对DO垂向分布的影响，同时也指示了冷水团边界区和长江口外海域涌升流的存在.此外，夏季长江口外东北部离岸低盐水团区的生物地球化学过程也对局地底层低氧区的形成有重要贡献.在夏季的长江口海域和秋季的黄海冷水团海域存在水体酸化区，其中长江口的酸化区范围与低氧区总体相吻合，秋季黄海冷水团底层酸化区也与DO低值区和冷水团范围基本一致.本研究结果可为南黄海和长江口海域低氧和酸化等生态环境问题的改善提供理论指导.

Dissolved oxygen distributions,hypoxic and acidification characteristics,and their controlling factors in the southern Yellow Sea and off the Changjiang Estuary

In this paper, based on hydrographic, chemical and biological data from two cruises conducted in August and November 2019, the spatial-temporal distributions of DO and relationships between DO petterns and physical-biogeochemical processes were focused in the southern Yellow Sea (SYS) and off the Changjiang Estuary (CE) during summer and autumn, and the hypoxic characteristics and acidification environment were explored. The results showed that the contents and distributions of DO corresponded to the current patterns, and the TWC (Taiwan Warm Current)-dominated area off the CE was characterized by low oxygen in summer, while a low-oxygen area existed in the bottom YSCWM (Yellow Sea Cold Water Mass) region in autumn. Influenced by the upwelling, the bottom oxygen-deficient waters off the CE could be uplifted to the upper layers and expanded northeastward. Moreover, the upwelled low-oxygen waters off the CE and the uplift of the middle DO-maximum layer in the YSCWM area were basically consistent with the uplifting trend of the thermocline in summer, which not only reflected the impacts of upwelling on the vertical distributions of DO, but also indicated the existence of upwelling around the YSCWM boundary and in the nearshore area off the CE. Besides, the offshore diluted water in the northeastern region of the CE also contributed to the formation of local low-oxygen zone. Acidification occurred off the CE during summer and also in the YSCWM-dominated area during autumn. Specifically, the acidified area off the CE was generally consistent with the hypoxic zone in summer, and the acidified area located within the YSCWM-dominated region in autumn was basically in accordance with the low-oxygen zone. Overall, the results of this study could provide theoretical guidance for the improvements of low oxygen and acidification in the SYS and off the CE.