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). The results focusing on the western Pacific freshwater pool indicate that the long-term averaged surface freshwater flux is well balanced by ocean dynamics, in which the subsurface processes account 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 largely controlled by surface freshwater flux. The opposite phase between the subsurface processes and the barrier layer thickness confirms the important influence of the barrier layer on vertical mixing and entrainment from below. 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 in the equatorial Pacific.

Energetic eddy activities are observed in the southern subtropical oceans. Among the three ocean basins, eddies are most active in the subtropical south Indian Ocean, where they induce a northward salt flux in the north and a southward salt flux in the south, resulting in a divergence of salt in the central part of the basin. Further analysis of satellite‐sea surface salinity observations shows that eddy‐induced meridional salt flux takes more than half of the salt gain from the excess of evaporation over precipitation out of the sea surface salinity maximum region in the south Indian Ocean, while this ratio falls below 19% in the South Pacific and 12% in the South Atlantic. The result may partially explain why salinity of the sea surface salinity maximum in the south Indian Ocean is the lowest among the three southern subtropical oceans.

The subduction and equatorward pathways of North Pacific Tropical Water (NPTW) are investigated using a simulated passive tracer of the consortium Estimating the Circulation and Climate of the Ocean (ECCO). The results demonstrate that the subduction of NPTW occurs in a large area that extends from about 150°E to 130°W between 20°N and 30°N, but the main subduction region lies in its eastern part. After subduction, the main body of NPTW first spreads westward in the North Equatorial Current. Then it splits into two branches. One flows northward in the Kuroshio upon reaching the western boundary, and the other enters the tropical Pacific either via its western boundary pathway (WBP) or interior pathway (IP). Less than half of the transport through the WBP can eventually reach the central and eastern Pacific by the Equatorial Undercurrent, while the rest is seen to flow into the Indian Ocean by the Indonesian Throughflow. The IP is found to play a significant role in equatorward transport of the NPTW. About 30% of the NPTW that reached the equatorial Pacific is transported through the IP.