Interannual to decadal variability of upper ocean salinity in the southern Indian Ocean and the role of the Indonesian Throughflow
Variability of oceanic salinity plays an important role in the basin scale ocean circulation and global hydrological cycle. Aiming to investigate the interannual to decadal variability of salinity in the upper layer Indian Ocean, Professor Shijian Hu and his colleagues made use of 15-year Argo observations since 2004 and data assimilating model outputs (1992–2015). They found that the southeastern Indian Ocean shows the strongest interannual to decadal variability of upper ocean salinity in the Indian Ocean. Westward propagation of salinity anomalies along isopycnal surfaces is detected in the southern Indian Ocean and attributed to zonal salinity advection anomalies associated with the Indonesian Throughflow and the South Equatorial Current. Through composite and salinity budget analyses, we show that horizontal advection is a major contributor to the interannual to decadal salinity variability of the southern Indian Ocean, and local air-sea freshwater flux plays a secondary role. The Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO) indices lead the salinity variability in the southeastern Indian Ocean by several months, such that the negative phases of the PDO and ENSO lead to low salinity anomalies whereas positive phases lead to high salinity anomalies. The Indonesian Throughflow plays an essential role in transmitting the PDO and ENSO related salinity signals to the Indian Ocean. A statistical model is proposed based on the PDO index, which successfully predicts the southeastern Indian Ocean salinity variability with a lead time of 10 months.
This work was supported by the Key Research Program of Frontier Sciences, CAS (QYZDB-SSWSYS023) and the National Natural Science Foundation of China (Grants 91858101, 41776018, and 41730534). This work has been published in Journal of Climate: Hu, S., Y. Zhang, M. Feng, Y. Du, J. Sprintall, F. Wang, D. Hu, Q. Xie, and F. Chai (2019), Interannual to decadal variability of upper ocean salinity in the southern Indian Ocean and the role of the Indonesian Throughflow, Journal of Climate, 32, 6403–6421, doi:10.1175/JCLI-D-19-0056.1.
Figure 1. Standard deviation (STD) of upper 400-dbar mean RG-Argo salinity (unit in 10-1psu) that is smoothed by 13-month running mean filter twice (Hu et al., 2019, JC).