Water Mass Processes Between the South China Sea and the Western Pacific Through the Luzon Strait: Insights From Hydrogen and Oxygen Isotopes

Abstract A comprehensive, depth specific (near‐surface to 3,700 m) water isotope (δD and δ18O) data set of 237 water samples collected from 20 different locations from the Northwest Pacific through the Luzon Strait to the Northern South China Sea (NSCS) are used to clarify the deeper understanding of water mass processes using δ18O‐salinity (S) and δD‐δ18O relations. Our study reveals that the δD‐δ18O correlation has a low slope and the δ18O‐S correlation has a high slope, which are related to the intrusion of the Kuroshio water and the influence of the coastal current above 200 m on the NSCS, respectively. The isotope mixing model showed that 15% is from the Kuroshio water, 40% from the South China Sea (SCS) Tropical Water, and 45% from the coastal current for water above 200 m in the NSCS. In the intermediate layer (300–1,200 m), a significant δ18O‐S correlation was found at depths of 300–700 m on the NSCS side, but no correlation was found on the western Pacific side, suggesting that the mixing of the water masses of the South China Sea Intermediate Water and the North Pacific Intermediate Water mainly occurs at depth in the NSCS. In the deeper water (below 1,200 m), positive isotopic values were found at depths below 1,500 m, which refuted the previous knowledge that positive isotopic values only exist in the Luzon Strait at depths above 1,000 m, and the positive isotope water mass would flow with the Deep Pacific Water into the deeper water of the SCS.