Mixed layer water mass analysis on the East China Sea inner shelf

We present a new extension of the traditional mixing triangle water mass analysis that is adapted for the mixed layer (ML) by including the atmospheric effects as a correction term in the original equations. The ML water mass analysis is then employed to determine the water mass contributions in the Changjiang river plume area based on observed hydrographic data in winter, summer and autumn of 2018. The comparison with the traditional method shows remarkable difference in the ratio between the Taiwan Strait Warm Water (TSWW) and the Kuroshio Subsurface Water (KSSW). In winter, a non-neglectable portion of TSWW is found east of 123°E, possibly due to the relaxation of the northeastern monsoon in March. In summer, both methods show that the upper ML water is mostly originated from TSWW and the lower layer from KSSW. The percentage of TSWW is however smaller with the new method. A second experiment using the Kuroshio Surface Water (KSW) in place of the KSSW reveals that the KSW intrusion is not evident in this region. During autumn, TSWW accounts for a major portion of the intrusion, and the cold and salty KSSW is only observed in the bottom layer below 50 m. The subsequent error analysis and sensitivity tests regarding to the relevant input parameters demonstrate the reliability and robustness of this new ML water mass analysis, but dynamic studies are still needed to fully understand the seasonal characteristics of the intrusion into the East China Sea shelf.