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A Triple mode of thermocline salinity variability in the tropical Pacific is revealed
September 07,2020

Variability of oceanic salinity, as an important indicator of the global hydrological cycle, plays a vital role in ocean circulation, global water cycle and climate variability such as the El Niño–Southern Oscillation (ENSO). For example, recent studies suggest that freshening (decreasing of salinity) of the upper ocean tends to intensify super typhoons in the western North Pacific Ocean by reducing their ability to cool the upper ocean (Balaguru et al., 2016), mixed-layer salinity variability may influence the El Niño-La Niña asymmetry (Guan et al., 2019), and salinity fluctuation is found to modulate the inter-annual to decadal variability of Indonesian Throughflow (Hu and Sprintall, 2016; 2017). However, for quite a long time, a lack of wide range and continuous observation of oceanic salinity results in short of understanding in its low-frequency variability on inter-annual to decadal time scales.

A research team from the IOCAS has been investigating the inter-annual to decadal variability of oceanic salinity in the tropical Indo-Pacific Ocean in recent years, working with several NPOCE members. The team made use of a 15‐year time series of in situ salinity observations from the international Argo program, the duration of which begins from the early 2000s, and covers a complete Pacific Decadal Oscillation (PDO) cycle and several ENSO cycles.

Fig. A carton showing the interannual-to-decadal variability of the Indo-Pacific Ocean salinity

In 2019, the team found that the PDO and ENSO modulate the salinity variability in the southeastern Indian Ocean through the Indonesian Throughflow and proposed a statistical model to predict the southeastern Indian Ocean salinity variability with the PDO index (Hu et al., 2019). In the tropical Pacific Ocean, PDO and ENSO also play a leading role in the inter-annual to decadal variability of oceanic salinity.

The team found that the thermocline salinity in the tropical Pacific Ocean is dominated by a well‐defined spatial pattern, namely a Triple MOde of thermocline Salinity (TMOS). Analysis suggests that the TMOS is a result of anomalous advection of the mean thermocline salinity as well as the mean advection of anomalous salinity associated with the ENSO and PDO. This progress has been published in the Journal of Climate and Journal of Geophysical Research: Oceans.

A better understanding of the observed TMOS pattern and Indian Ocean salinity variability may help us to better understand how the climate may form and transform the Indo-Pacific water masses.

Links:

Hu, S., and Coauthors, 2019: Interannual to Decadal Variability of Upper-Ocean Salinity in the Southern Indian Ocean and the Role of the Indonesian Throughflow. J. Climate, 32, 6403–6421, https://doi.org/10.1175/JCLI-D-19-0056.1.

Hu, S., Sprintall, J., Guan, C., Hu, D., Wang, F., Lu, X., & Li, S. (2020). Observed triple mode of salinity variability in the thermocline of tropical Pacific Ocean. Journal of Geophysical Research: Oceans, 125, e2020JC016210. https://doi.org/10.1029/2020JC016210.

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