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Abstract

Bottom- to intermediate-water formations are crucial for meridional circulation and ventilation in the marginal seas as well as global oceans. Observations in the East/Japan Sea (EJS) suggested that open-ocean convection usually occurs south of Vladivostok and that deep convection occasionally occurs along the continental slope, resulting in bottom water formation. Open-ocean and slope convection processes in the EJS were investigated using large-eddy simulation. Slope convection was demonstrated as dense water, formed by strong wintertime cooling in the shelf, flows down along the continental slope as a bottom Ekman current. The properties of the initial dense water were relatively well conserved during slope convection, but they changed rapidly by mixing with the surrounding waters in the open ocean. Accordingly, slope convection penetrated deeper compared to open-ocean convection under the same surface heat flux. Our numerical experiments showed that, under 20 days of 200 W m^-2 surface cooling, slope convection reaches depths greater than 2,700 m, whereas open-ocean convection reaches approximately 700 m depth. The results suggest that slope convection is a potential ventilation process for the deep- and bottom-water formations, whereas open-ocean convection contributes to the intermediate- and central-water formations in the EJS. Additional experiments with various topography revealed that the speed of the convective plume was proportional to the slope inclination; the initial properties remained relatively well conserved on a slope of small inclination. The slope convection could be accelerated by a salinity increase in the shelf due to brine rejection from sea-ice formation.