Upwelling Variability in the Western South China Sea Associated With Global Climate Change

Abstract

In this study, the changes in interannual variability of upwelling in the Western South China Sea (SCS) from 1958 to 2015 and their relationships with climate variability are investigated using reanalysis data and numerical simulations. Our results show that the interannual variability of upwelling in the three main upwelling regions, that is, the East Coast of Vietnam (VE), Southwest of Hainan Island (HNW), and East of Hainan Island (HNE), has significantly changed after the 1990s, influenced by the changes in the variability of the El Niño Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD). Specifically, the variance of upwelling in VE and HNW has increased by over 20%, while that of HNE has decreased by 30% after the 1990s. The effects of ENSO and IOD on the upwelling in VE and HNW have significantly enhanced during both positive and negative phases after the 1990s, while their effects on upwelling in HNE have significantly weakened during negative phases. Wind and Ekman pumping anomalies are the primary forces driving the changes in upwelling. However, for the negative phase of ENSO, anomalies in large-scale circulation dominate the variability of upwelling after the 1990s. Our study highlights the complexity of the mechanisms driving the variability of upwelling in the SCS and the importance of ENSO and IOD in predicting their long-term changes.