Decadal trends of the upper ocean salinity in the tropical Indo-Pacific since mid-1990s.

Yan Du,Ming Feng,Tianyu Wang,Ningning Zhang,Susan Wijffels,Yuhong Zhang

doi:10.1038/srep16050

Abstract

A contrasting trend pattern of sea surface salinity (SSS) between the western tropical Pacific (WTP) and the southeastern tropical Indian Ocean (SETIO) is observed during 2004–2013, with significant salinity increase in the WTP and freshening in the SETIO. In this study, we show that increased precipitation around the Maritime Continent (MC), decreased precipitation in the western-central tropical Pacific, and ocean advection processes contribute to the salinity trends in the region. From a longer historical record, these salinity trends started in the mid-1990s, a few years before the Global Warming Hiatus from 1998 to present. The salinity trends are associated a strengthening trend of the Walker Circulation over the tropical Indo-Pacific, which have reversed the long-term salinity changes in the tropical Indo-Pacific as a consequence of global warming. Understanding decadal variations of SSS in the tropical Indo-Pacific will better inform on how the tropical hydrological cycle will be affected by the natural variability and a warming climate.

Highlights

A contrasting trend pattern of sea surface salinity (SSS) between the western tropical Pacific (WTP) and the southeastern tropical Indian Ocean (SETIO) is observed during 2004–2013, with significant salinity increase in the WTP and freshening in the SETIO
A remarkable hiatus of the global warming has occurred since the beginning of the 21th century[10], which is tied to sea surface temperature (SST) cooling in the eastern equatorial Pacific and intensification of the Walker Circulation[11,12,13]
The WTP becoming saltier and the SETIO becoming fresher are the dominant features in the linear trends of SSS from Array for Real-time Geostrophic Oceanography (Argo) float data in the global ocean during 2004–2013 (Fig. 1a)

Summary

Results

Surface salinity trends and intensification of Walker Circulation. The WTP becoming saltier and the SETIO becoming fresher are the dominant features in the linear trends of SSS from Argo float data in the global ocean during 2004–2013 (Fig. 1a). The first EOF mode (EOF1) of the SSS shows contrasting variations between the South China Sea (SCS)-SETIO and the WTP, high in the east and low in the west, explaining 20% of the total root mean square (RMS) variance, which increase to 35% with only low-frequency signals considered (Fig. 4a) This pattern mainly reflects a La Niña-like feature[32]. The atmospheric reanalysis fields reveal that the intensification of the Walker Circulation is a key driver of SSS trends It enhances the precipitation over the Maritime Continent and adjacent ocean and reduces precipitation over the western-central tropical Pacific, resulting in a salinfication trend in the WTP and freshening trend in the SCS-SETIO (Fig. 5).

Methods

Author Contributions

Additional Information