Physical Controls of Seasonal Hypoxia in Jakarta Bay: Monsoon‐Driven Circulation, Stratification, and Management Implications

Shallow semi‐enclosed tropical bays are highly vulnerable to seasonal hypoxia due to the combined influence of monsoon‐driven circulation, freshwater input, and water‐column stratification. In Jakarta Bay, understanding how physical processes regulate oxygen dynamics is essential for effective water–environment management in a densely populated coastal setting. This study integrates field observations and three‐dimensional hydrodynamic modeling to assess seasonal variations in circulation, stratification strength (quantified using potential energy anomaly, PEA), water‐mass transport, and bottom dissolved oxygen across the Southeast Monsoon, inter‐monsoon, and Northwest Monsoon periods. The results show that hypoxia is most extensive during the Inter‐monsoon (151 km 2 ), when elevated stratification coincides with reduced circulation and limited ventilation. In contrast, hypoxia becomes minimal during the Northwest Monsoon, despite substantial freshwater input and pronounced stratification signals, owing to intensified wind‐driven circulation and enhanced water exchange that promote bottom‐water oxygen renewal. The Southeast Monsoon represents an intermediate condition characterized by moderate stratification and partial ventilation. Quantitative estimates of volume transport (VT) across the bay mouth demonstrate a strong coupling between monsoonal wind stress and circulation strength, highlighting physical exchange as a primary control on oxygen variability. By emphasizing physically observable indicators—wind stress, stratification metrics, and water‐mass transport—this study provides a practical framework to support hypoxia monitoring, early warning systems (EWS), and adaptive water–environment management in Jakarta Bay and other monsoon‐influenced tropical coastal systems.