The reflux of water transport in the intermediate layer of Luzon Strait

Based on Lagrangian particle tracking experiments using long-term, high-resolution reanalysis data, we investigate the pathways of water transport and reflux at different depths in the intermediate layer of the Luzon Strait (LS). Reflux is defined as the phenomenon where particles, once released at the 121°E section, subsequently return to the same section. The results indicate that the majority of reflux occurs within 60 days and can be categorized into two scenarios according to the return time. The case with the shorter return time involves higher-frequency flow variations in the LS. In contrast, the case with the longer return time not only modifies the zonal transport across the LS but also facilitates meridional connections between the northern outflow toward the western Pacific Ocean and the central inflow into the South China Sea (SCS). The pattern and seasonal variations of reflux vary significantly with depth. At the 500 m depth, the reflux is mainly attributed to the central inflow associated with the Kuroshio intrusion, with only 5% of the northern outflow returning to the 121°E section. At the 1250 m layer, the northern outflow is more prone to reflux, with 60% flowing back to the section, while the reflux of central inflow results in only a small fraction of the inflow water returning to the western Pacific Ocean. These findings highlight the critical role of reflux processes in regulating intermediate-layer water exchanges through the LS, contributing to a more comprehensive understanding of the interactions between the western Pacific and the SCS.