Examining the salinity change in the upper Pacific Ocean during the Argo period

During the Argo period, the Pacific Ocean as well as the global oceans became saltier in the upper-200 m from 2005 to 2015, with a significant spatial variability. Using Argo-based observations and the Estimating the Circulation and Climate of the Ocean (ECCO), a salinity budget analysis in the upper 200 m was conducted to investigate what controls the recent observed salinity change in the Pacific Ocean. The results showed that the increasing salinity since 2005 was mainly caused by a reduction of surface precipitation. The ocean advection dampened the surface freshwater anomalies and rebuilt regional salinity balance. Both precipitation and advection are closely associated with the sea surface wind anomalies, suggesting the wind-driven changes in the ocean salinity field. A further analysis using an ocean objective analysis product and model simulations in addition to ECCO suggests that the recent salinity pattern since 2005 are related to the Interdecadal Pacific Oscillation (IPO). This study also highlights the strong regulation of the ocean salinity change by natural decadal variability in the climate system.