Deep water ventilation in the South China Sea

Abstract

As the western Pacific intermediate water funnels into the deep basin of the South China Sea through the Luzon Strait, how does it eventually upwell? This question is examined by releasing a passive tracer, which is uniformly distributed in the deep basin initially, in a three-dimensional, climatology-driven circulation model. Subsequent advection and diffusion of the tracer are studied in relation to the circulation in the deep basin. Two primary regions of deep upwelling responsible for deep water renewal are identified: southwest of Taiwan and off Vietnam. The former is associated with inflow of water at the sill depth of the Luzon Strait, while the latter is induced by orographic lifting of currents over the continental margin. Upwelling off Vietnam begins in August near a topographic bump at 16°N, 114°E, expands southwestward until December, and is weakened by downward motion during the rest of the year. Simultaneous occurrence of deep downwelling off Luzon and Palawan with deep upwelling off Vietnam suggests that the upward tracer dispersion is modulated by basin-wide circulation at mid-depths. At shallow depths, upwelling is present off Vietnam in summer and off northwest Luzon in winter, and shelf break upwelling appears on the edge of Sunda Shelf from October to December, when the southward coastal jet impinges on the shelf. However, these shallow upwelling processes have little effect on the deep water renewal. These findings are supported by climatological data.