Coastal hypoxia in the densely-populated Indian Ocean has dramatic consequences for ecosystems and ecosystem services such as fisheries and coastal protection. A major challenge to anticipate the risks is to understand the spatial and temporal variability and the physical and biological drivers that control coastal oxygen levels and hypoxia in the region. Here we use in-situ observations and a high-resolution (1/12-degree) biophysical model of the Indian Ocean to map areas with heightened vulnerability to coastal hypoxia and identify the drivers of coastal oxygen dynamics spatiotemporal variability. We find strong regional disparities in the mechanisms and temporal scales that govern coastal hypoxia: seasonal upwelling in the eastern Arabian Sea, interannual upwelling/downwelling linked to Indian Ocean Dipole events in the eastern Bay of Bengal, intraseasonal fluctuations introduced by coastal currents, Kelvin waves and eddies along the western Bay of Bengal, and biologically- driven oxygen variations at the mouth of major rivers in the northern Bay of Bengal (e.g. Ganges-Brahmaputra and Irrawaddy and Sittang Deltas). This basin-scale mapping identifies regions where intraseasonal hypoxia (e.g. western Bay of Bengal) challenges the prediction of these events and calls for intense monitoring, and regions where seasonal and interannual hypoxia (e.g., eastern Arabian Sea, river deltas, eastern Bay of Bengal) facilitates the prevention of the adverse impacts on coastal ecosystems and their services.

coastal hypoxia,northern Indian Ocean,Indian Ocean Dipole,intraseasonal variability,Seasonal variability