Vertical distribution of δ13C of dissolved inorganic carbon in the northeastern South China Sea

The δ13C of ΣCO2 along with dissolved oxygen and nutrients in seawater collected near the Luzon Strait were analyzed to provide new data regarding water exchange between the South China Sea and the Pacific. Sampling covered the area 20–22°N and 118–120°E in April, June, and October 1995. Three stations were repeated during these cruises. In addition, sections along 119° and 120°E near the entrance of Luzon Strait were constructed. The depth profiles of δ13C from the nine stations presented in this study are similar to those reported from the open ocean. Correlation with chemical parameters (apparent oxygen utilization and phosphate) aids in the interpretation of the δ13C data. An apparent shift of δ13C profiles between cruises but at the same site was observed and was concluded to be related not to the seasonal change, but to the presence of different water masses exhibiting distinct θ-S relationships.