Numerical simulation of the dual-core structure of the Bohai Sea cold bottom water in summer

Regional Ocean Modeling Systems (ROMS 3.0) and the k-epsilon turbulence closure scheme has been applied to investigating the seasonal evolution of the thermsocline in the Bohai Sea. The simulation reproduces the stratifications lasting from early April to early September and reveals the existence of marked Asymmetric Dual-Core Cold Bottom Water (ADCCBW) in the south and north depression basin respectively under the thermocline. The bottom temperature in the north depression is about 1-4 degrees C lower than that in the south depression basin which is in good agreement with observations. Model results suggest that the local bathymetry characteristics and inhomogeneous net heat flux due to the latitude difference are the major cause for the early formation of the ADCCBW. Numerical Lagrangian drifter experiments support the finding that the ADCCBW is maintained throughout the stratification periods by the inflow of cold bottom water from the northern Yellow Sea and deep channel in the western side of Liaodong Peninsula. The inflow cold water contributes to the north depression basin distinctively larger than to the south one. Tidal mixing enhances the bottom temperature asymmetry between the two basins.