Observations and models show that global water cycle has been intensified due to global warming, which is evident by a clear ocean fingerprint of salinity change. After 2005, Argo network reached near-complete global coverage, providing the best observations than ever for the salinity changes. During this period, the Global and Pacific salinity experience an opposite change at vertical layers: the ocean saltier at the upper-200m and fresher within 200 to 600m, with distinctive regional signatures compared with long-term pattern. Our study aims to explore how the upper-200m salinity pattern forms by using observations and reanalysis data.

An upper-200m salinity budget analysis, based on an ocean state estimate ECCO v4.3 (Estimating the Circulation and Climate of the Ocean version 4 release 3), was conducted to access the recent decadal trend reversal in Pacific (rising after 2005) and investigate the mechanisms controlling the increasing trends. The budget diagnostics in the major salinity increasing regions at the upper-200m indicate that the salinity increases since 2005 were contributed to the freshwater changes near the sea surface due to the precipitation forcing, together with the ocean advection mainly forced by the wind anomalies. Further analysis suggests the decadal changes of these patterns since 2005 are likely related to the Interdecadal Pacific oscillation (IPO). This study highlights a significant regulation of the ocean salinity change by natural decadal variability in the climate system.