Mixed Layer Salinity Budget in the Fresh Pool of Western Pacific

The mixed layer salinity (MLS) budget of the tropical Pacific is investigated using results from a model of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO), in which a simplified calculation method of the vertical entrainment is applied. The results focusing on the western Pacific fresh pool indicate that the long-term averaged surface freshwater flux is well balanced by ocean dynamics, in which the subsurface process accounts for the major part. The MLS budget shows significant seasonal and interannual variability, as a consequence of interplay among surface freshwater flux, advection, mixing, and vertical entrainment. On seasonal time scale, both the MLS and mixed layer depth are controlled by surface freshwater flux. The negative correlation between the subsurface processes and barrier layer thickness confirms the effect of the barrier layer on vertical mixing and entrainment at depth. On interannual time scale, all the MLS budget terms show significant ENSO signal, which in turn is highly correlated with the salinity front and barrier layer thickness variability.