The influence of non-tidal ocean loading in the South China Sea on iGrav-048 superconducting gravimeter observations at Haikou Station

Non-tidal ocean loading (NTOL) is a significant environmental factor affecting gravity observations in coastal areas. Its non-periodic characteristics and regional dependence increase the difficulty of data analysis and signal separation. The Haikou superconducting gravimetry station, located in the northern part of Hainan Island, is situated close to the South China Sea. It is influenced by complex regional oceanic dynamic processes, and the NTOL signal in its gravity observations is particularly prominent. Based on continuous superconducting gravimeter (SG) observations from the iGrav-048 at the Haikou station and high-resolution global sea surface height data from the Copernicus Marine Environment Monitoring Service (CMEMS), we calculate the gravity variations and vertical deformations caused by NTOL in the South China Sea using the mass-loading Green’s function convolution method. The estimates are validated by comparison with products from the MPIOM model provided by the German Research Centre for Geosciences (GFZ). The results show that NTOL signals in the South China Sea should be the primary source of gravity residuals at the Haikou station. The CMEMS model shows a correlation coefficient of approximately 0.8 with the observations, and the simulated NTOL signal explains approximately 40% of the total SG residuals. The maximum gravity change due to NTOL is estimated to be 1.8 μGal based on the CMEMS model. While the CMEMS and MPIOM models show good agreement in overall trend (R=0.88), CMEMS performs better in simulating high-frequency signals due to its higher spatio-temporal resolution. This highlights the importance of high-precision regional ocean models for improving the modeling and correction of NTOL signals. This study systematically evaluates the impact of South China Sea NTOL on SG observations at the Haikou station, providing a scientific basis for the processing of coastal gravity data in the region. The findings suggest that incorporating NTOL corrections into coastal superconducting gravity data processing can effectively improve data reliability and geophysical interpretation, offering valuable insights for advancing regional ocean loading effect research and related geodetic applications.