Weakened circulation in the deep South China Sea triggered by prolonged warming

Ocean warming, which affects the ocean hydrodynamic environment, changes marine ecosystems, and impacts both regional and global climates, has been widely observed in recent decades. However, the effects on deep circulation in the Pacific Ocean and its marginal seas, such as the South China Sea, have rarely been reported. Here we assess circulation responses in the South China Sea at depths exceeding 2 400 m via reanalysis datasets and numerical simulations. The results suggest that ocean warming has weakened circulation in the deep ocean in recent decades. The variation in circulation is driven by changes in the horizontal density gradient. However, warming also enhances diapycnal diffusivity, which can accelerate circulation, counteracting deep circulation weakening to some extent. Understanding regional responses to deep ocean circulation plays an essential role in advancing future global scale understanding of hydrodynamic changes, with implications for climate change and economic consequences. Ocean warming has weakened deep circulation in the South China Sea in recent decades, according to analyses using reanalysis datasets and numerical simulations.