The Seasonal Variation of the Anomalously High Salinity at Subsurface Salinity Maximum in Northern South China Sea from Argo Data

Hui Shen,Yuezhang Xia,Zhiguo He,Jianlong Li,Li Li

doi:10.3390/jmse9020227

Abstract

The large variations in salinity at the salinity maximum in the northern South China Sea (NSCS), as an indicator for the changes in the Kuroshio intrusion (KI), play an important role in the hydrological cycle. The high salinity here is more than 34.65 at the salinity maximum and is intriguing. In the past, the salinity was difficult to trace in the entire NSCS over long periods due to a lack of high-quality observations. However, due to the availability of accumulated temperature and salinity (T-S) profiles from the Argo program, it is now possible to capture subsurface-maximum data on a large spatiotemporal scale. In this study, the salinity maximum distributed in the subsurface of 80 to 200 m at a density of 23.0–25.5 σθ was extracted from decades of Argo data (on the different pressure surfaces, 2006–2019). We then further studied the spatial distribution and seasonal variation of the salinity maximum and its anomalously high salinity. The results suggest that a high salinity (salinity > 34.65, most of which is located at the shallow depths < 100 m) at the subsurface salinity-maximum layer often occurs in the NSCS, especially near the Luzon Strait, which accounts for about 23% of the total salinity maximum. In winter, the anomalously high salinity at the shallow subsurface salinity maximum can extend to the south of 17° N, while it rarely reaches 18° N and tends to locate at deeper waters in summer. The T-S values of the anomalously high-salinity water are between the mean T-S values in the NSCS and north Pacific subsurface water, implying that the outer sea water gradually mixes with the South China Sea water after passing through the Luzon Strait. Finally, our results show that the factors play an important role in the appearance and distribution of the anomalously high salinity at the subsurface salinity maximum, including the strength of the Kuroshio intrusion, the local wind stress curl and the anticyclonic eddy shedding from the loop current.

Highlights

IntroductionThe subsurface salinity change patterns provide further indications of an intensified water cycle, including an accentuation of the upper layer salinity contrast between the upper thermocline salinity maximum and the lower thermocline salinity minimum [1,2]
4a shows that observation time, which is consistent with previous
The high salinity located at the shallow depth (

Summary

Introduction

The subsurface salinity change patterns provide further indications of an intensified water cycle, including an accentuation of the upper layer salinity contrast between the upper thermocline salinity maximum and the lower thermocline salinity minimum [1,2]. The salinity dynamics in the northern South China Sea (NSCS, 15–21◦ N, 105–121◦ E) play an important role in the water cycle between the SCS and North Pacific Tropic ocean (Figure 1). The salinity dynamics, especially at the maximum and minimum layer in this region, have attracted much interest from researchers worldwide, for the maximum and minimum 4.0/).

Results

Discussion

Conclusion