Effects of the Changjiang (Yangtze) River discharge on density stratifications in the Yellow and East China Seas

Abstract

Freshwater from the Changjiang River is a key factor controlling density stratifications in the Yellow and East China Seas. Previous observations revealed anexistence of a barrier layer due to the Changjiang River Discharge (CRD) although the observation sites were limited near the Changjiang River mouth or its southern areas. In a previous study, a numerical experiment was performed to investigate effects of the CRD on sea surface currents and temperature, but it was not satisfactory because of the coarsegrid resolution and truncation of ocean margins shallower than the mixed layer depth. In this research, we adopted an ocean general circulation model strongly resolving the Yellow and East China Seas without relaxation of surface salinity to investigate effects of the CRD on the density stratifications and relevant surface temperature changes. Comparison experiments of considering the CRD and blocking the CRD for 1960-2001 using ECMWF Re-analysis data showed that the CRD increases surface temperature in August accompanying with surface freshening. The surface warming didn’t occur all the season because of cold water advection from north due to strengthened horizontal salinity gradient by the CRD input. A sensitivity experiment, which was performed by year-to-year variation of the CRD only and constant annul forcing fields, showed that the warming due to the CRD in August concurred with thicker barrier layer and shallower mixed layer. The relationship between the CRD and surface temperature change was investigated with the formation of the barrier layer and the mixed layer.