Program     Evolution of Deep Sea Processes in the South China Sea       Poster Three-dimensional pathways of water masses in the South China Sea: a modeling study P-SPS6-03 Zhiqiang Liu* , Division of Environment and Sustainability, The Hong Kong University of Science and Technology Jianping Gan, Department of Ocean Science and Department of Mathematics, The Hong Kong University of Science and Technology Presenter Email: liuzhq@connect.ust.hk We conduct a numerical Eulerian analysis on the Lagrangian characteristics of South China Sea (SCS) water masses. This is the first study to investigate the water pathway and residence time in response to time-dependent, three-dimensional basin circulation in the SCS. The circulation of the SCS is largely determined by westward intrusions of the northwestern Pacific waters in the upper layer (0-750 m) and deep layer (>1500 m), and by an eastward extrusion in the intermediate layer (750-1500 m) through Luzon Strait (LS). The waters in these three layers are interlinked to sustain the three-dimensional circulation in the SCS. The upper intrusive waters flow cyclonically and have a residence time of ~3 years before they subduct into a deeper layer or exit the SCS through surrounding straits. The intrusive denser waters in the deep layer flow along the northern slope and reside for ~25 years in the northern basin (north of 13°N), where a strong subduction occurs. A cyclonic circulation exists in the deep layer in the southern basin (south of 13°N), where a subduction of intermediate waters occurs over its eastern side and a deep upwelling exists over its western side. The water in the deep southern basin has a residence time of ~40 years. The upwelled deep waters and the subducted waters from the upper layer form the intermediate water, where waters circulate anti-cyclonically towards LS and have a longest residence time (~42 years). These findings are supported by the spatial variation in the observed potential density variance.