Hypoxia has been observed worldwide and causes great damage to marine ecosystems. In the northeastern mariculture areas of the Shandong Peninsula, summer oxygen depletion and even hypoxia have been observed in the bottom layer, but the underlying dynamics are still poorly understood. In the current study, the physical controls of variations in bottom layer oxygen concentrations in summer and their interannual variations in the northeastern mariculture areas of the Shandong Peninsula were first investigated using in situ observations collected during 2016–2020. Over the past 5 years, the dissolved oxygen (DO) concentrations of the bottom layer have ranged from 0.8 to 13.0 mg L⁻¹ and exhibited a robust annual cycle, with the lowest value occurring in August. Hypoxia events covering several days were observed intermittently in the summers of 2016 and 2017. Summer oxygen depletion was caused by the combined effects of ocean stratification and enhanced biogeochemical oxygen consumption. At the interannual time scale, stratification and bottom layer DO concentrations showed synchronous variations and both peaked in 2018. The underlying mechanism was related to bottom layer currents, which were created by southerly monsoon winds. Strong/weak southerly surface winds induced a strong/weak bottom shoreward advection of cold, oxygen‐rich water and resulted in strong/weak stratification and high/low DO concentrations. The results provide a good reference for coastal mariculture management in the Shandong Province and enrich our understanding of the global distribution of coastal hypoxia.

A severe coral bleaching event occurred in the Beibu Gulf during boreal summer 2020. This event was caused by record-breaking warm sea surface temperature (SST) anomalies in the northern South China Sea (NSCS). Anomalous anticyclones (AACs) over the NSCS linked to the Indian Ocean warming and La Niña induced the extreme NSCS warming. In May–July 2020, anomalous anticyclonic-shear easterlies appeared over the tropical western Pacific as a Kelvin wave response to the Indian Ocean warming. These easterlies resulted in an AAC over the NSCS and tropical northwestern Pacific via the Ekman dynamics. Besides, the anomalous easterlies increased moisture fluxes from the Pacific to the Maritime Continent (MC), enhancing the MC convection and thus supporting the NSCS AAC via an anomalous Hadley circulation. In this stage, the increased incident shortwave radiation induced by the NSCS AAC was the major contributor to the NSCS warming. In September 2020, anomalous equatorial Pacific easterlies associated with the La Niña could trigger an NSCS AAC by enhancing the MC convection. The resultant AAC warmed the NSCS SST anomalies mainly by increasing downward latent heat flux and shortwave radiation. Downward heat advection associated with the NSCS AAC also contributed to the extreme NSCS warming.

Decadal variation of the Kuroshio intrusion into the South China Sea (KIS) during 1992–2016 is investigated using high‐resolution Hybrid Coordinate Ocean Model reanalysis data. The results indicate that both the yearly occurrence frequency of the Kuroshio intrusion and Luzon Strait transport show significant decadal variations and were generally high in approximately 1993, 2003–2004, and 2015–2016 and low in 1998–1999 and 2009–2010. The KIS is closely connected to the decadal oscillation of the meridional sea surface height anomaly (SSHA) gradient west of the Luzon Strait (LS). Further analyses reveal that large‐scale wind forcing in the western tropical Pacific Ocean is a major factor regulating decadal variation of the KIS, while local wind forcing has little impact. Cyclonic wind stress curl anomalies (WSCAs) over the western tropical Pacific Ocean induce negative SSHAs that propagate westward to the eastern coast of the Philippines via upwelling Rossby waves, weakening the Kuroshio transport and consequently enhancing the KIS. In addition, signals of negative SSHAs can propagate clockwise along the Philippines as coastal Kelvin waves and hence strengthen the northward SSHA gradient west of the LS, eventually leading to a stronger KIS. The situation is reversed when anticyclonic WSCAs prevail in the western tropical Pacific Ocean. The Philippines‐Taiwan Oscillation is linked to decadal WSCAs over the western tropical Pacific Ocean and hence regulates the decadal KIS.