Hypoxia disaster in waters adjacent to the Changjiang estuary

Abstract. Based on observational data from ten cruises carried out in 2012 and 2013, the distribution of dissolved oxygen (DO) and hypoxia (DO < 2.0 mg L−1) evolution in waters adjacent to the Changjiang estuary are studied. The linkage between summer hypoxia and hydrodynamic conditions is explored. The results suggest that hypoxia frequently occurred from June to October to the south of the Changjiang estuary near the 30–50 m isobaths and was prone to happen under strong stratification without the presence of the Kuroshio Subsurface Water (KSW). Over the Changjiang Bank, hypoxia mainly occurred in July, August and September. Low-oxygen areas initially exist under strong stratification induced by the spreading of the Changjiang Diluted Water (CDW), and develop into hypoxia centers due to the lack of supplement of the relatively DO-rich Yellow Sea Water and the KSW. The evolution of hypoxia in a year is influenced by conditions of the shelf circulation especially the paths of the KSW and the CDW. Thus, further study on the salinity evolution in the bottom layer of the water to the south of the Changjiang estuary and in the surface layer over the Changjiang Bank, that indicates the extensions of the KSW and the CDW, is needed for improving the hypoxia prediction.