Surface water δ18O in the marginal China seas and its hydrological implications

Abstract

Surface water δ18O distribution in the marginal China seas (including the south Yellow and East China Seas, YECS, and the northern South China Sea, NSCS) and its relationship with salinity were investigated to gain insight into the surface hydrological processes in these seas. In the YECS where δ18O and salinity varied in relatively large ranges, seasonally different slopes of δ18O-salinity linear fits, i.e. 0.26 ± 0.02 in summer and 0.23 ± 0.01 in winter, were observed. In the NSCS, δ18O and salinity ranged narrower than in the YECS, and exhibited a similar linear relationship in winter but a poor correlation in summer. The saline surface water end-members were nearly identical in δ18O and salinity in both the YECS and NSCS and showed different values between summer and winter. These saline end-members were distinct from the reported values of the Kuroshio water (KW), which might be related to modification of KW mainly by atmospheric forcing. Using a simple mixing model, we showed that the observed significant linear δ18O-salinity relationships in the YECS were caused mainly by great terrestrial freshwater influx. The observed poor correlation between δ18O and salinity in the summer NSCS was likely associated with the relatively minor runoff contribution, although in wet period, to the freshwater end-member. The still good relationship in the NSCS during the dry wintertime, however, was attributable to the strong China Coastal Current flowing from the ECS to the NSCS through the Taiwan Strait driven by the prevailing northeast monsoon.