Abstract
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.
Highlights
Ocean salinity is a fundamental element for ocean stratification and large-scale ocean circulation (Roemmich et al 1994; Lagerloef et al 2010)
Recent Array for Real-time Geostrophic Oceanography (Argo)-based observations show an increase in global salinity in the upper 200 m and a decrease for 200–600 m after 2005, with distinctive regional patterns compared with the long-term patterns
The inter-basin comparison further demonstrates that the Pacific Ocean plays a key role in setting the global mean upper-600 m salinity changes during 2005–2015
Summary
Ocean salinity is a fundamental element for ocean stratification and large-scale ocean circulation (Roemmich et al 1994; Lagerloef et al 2010). The long-term change of ocean salinity is a key indicator of hydrological cycle change It shows a response of anthropogenic global warming (Hartmann et al 2013; Rhein et al 2013; Levang and Schmitt 2015). The large-scale freshening of the Pacific intermediate water over the second half of the last century are found in the collected hydrographic sections, which can be attributed to an increasing freshwater input over the source region due to the anthropogenic global warming (Wong et al 1999). Besides these long-term changes, the inter-annual and decadal-scale salinity changes are significant.
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