Effects of Reduced Yangtze River Discharge on the Circulation of Surrounding Seas

Abstract

A regional model of the western Pacific Ocean with 1/6o resolution is used to investigate possible effects of reduced Yangtze River discharge on the circulation of surrounding seas. To the extent of data availability, the model is mostly driven by monthly climatological winds and inflows/outflows through open-ocean boundaries. With climatological discharge rate, the Yangtze River plume disperses to the northeast in summer but follows the China Coastal Current (CCC) to the south in winter. While a substantial amount of the summer plume is retained in the southern Yellow Sea and northern East China Sea until the arrival of winter northerly monsoon, the winter Yangtze River discharge is able to escape freely to the south through advection by the CCC. The source water of the CCC is mainly comprised of winter discharge from Yangtze River, remnants of Yangtze River plume water retained in areas northeast of the river mouth from the preceding summer, Yellow Sea water and even some of the Bohai water. The effect of reduced Yangtze River discharge is highly asymmetric between summer and winter. Summer reduction produces an expansive, positive salinity anomaly northeast of the Yangtze River mouth. The response is rather swift and directly proportional to the reduction of freshwater supply. Winter reduction of freshwater discharge from the Yangtze River leads to higher salinity in the CCC south of the river mouth. The winter insensitivity of the CCC to reduced Yangtze outflow arises because the CCC is fed by multiple sources, some of which are not related to winter discharge from Yangtze River. In the highly unlikely event that the Yangtze River discharge is terminated for multiple years, the source water of the CCC will be dominated by the Yellow Sea and even Bohai waters.

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