On steric and mass-induced contributions to the annual sea-level variations in the South China Sea

The steric sea level (SLAsteric), water-mass change (SLAmass) and their contributions to the sea level anomaly (SLA) in the South China Sea (SCS) are studied by using altimetry data, Ishii data and GRACE data. Annual harmonic results and correlation analysis indicate that the SLAsteric has a significant contribution to the SLA over deep basin and that its phase leads SLA 1–3 months in different parts of the SCS, whereas the SLAmass explains the SLA to a great extent over shallow water areas. The area-averaged SLA in the western SCS has an amplitude of ∼ 7.6 cm and a phase of ∼ 360°, which is ∼ 3.8 cm higher and peaks ∼ 108° later than SLAsteric. The SLAmass has an amplitude of ∼ 6.3 cm and a phase of ∼ 337°. The simultaneous correlation coefficient between SLA and SLAmass is 0.78, which indicates that mass variation dominates the sea-level variation in the western SCS. Unlike the western SCS, the area-averaged SLA in the central SCS peaks at 254° with a smaller amplitude of ∼ 3.3 cm, which is ∼ 1.8 cm lower and peaks ∼ 15 days later than corresponding SLAsteric. The simultaneous correlation coefficient between SLA and SLAsteric is 0.81; therefore, the contribution of steric variation to the sea-level variation is dominant in the central SCS.