Deep and intermediate exchange patterns through the Luzon Strait as revealed by synoptic hydrographic observation

Based on full-depth hydrographic observations conducted synoptically, water properties across the Luzon Strait (LS) ridges were compared to investigate the deep and intermediate exchange patterns through the LS. The analysis indicates that, in the sense of vertical distribution of water properties below 1800 m, the Lanyu/Luzon Ridge system rather than the Heng-Chun Ridge is the key barrier that separates the South China Sea (SCS) from the northwestern Pacific (NWP). Below 1800 m, the overflow is subjected to strong mixing in the Luzon Trough (LT). The analysis provides the synoptic snapshot of the LS overflow, which confirms its previously suggested pathway. It is also evident that the intermediate outflow through the LS may occur in 850–1800 m, a much wider depth range than that previous realized. In the 1400–1800 m range, the outflowing SCS water shows little property changes, and hence appears to be advection dominated with little influence of mixing. In the 850–1150 m range, the outflow water appears to be interleaved and mixed with the NWP water. Therefore, the LS intermediate outflow is more complex in both space and time than was believed previously. •Full-depth, synoptic hydrographic observations were conducted in the LS area.•Deep and intermediate exchange patterns through the LS are depicted.•The synoptic snapshot of the LS overflow is presented.•The LS intermediate outflow is complex in both space and time.