Recently, the research team led by Prof. Zhou Chunfu, Prof. Zhao Wei and Prof. Tian Jiwei from the Frontier Science Center of Deep Ocean Multispheres and Earth System (OUC) has made significant progress in the Deep Circulation between Luzon Strait and South China Sea. For the first time, the team conducted continuous observation to identify a long-term enhancement of the deep-water overflow in the Luzon Strait. Its research outcome was published in Nature Communications under the title “Increasing deep-water overflow from the Pacific into the South China Sea revealed by mooring observations” on April 10.

The South China Sea is a significant spot for oceanic deep water upwelling, and it is critical for the circulation of momentum, heat and materials. The Luzon Strait is the only deep-water corridor linking the South China Sea and the Northwest Pacific. Trillions of tons of North Pacific deep water enters the South China Sea as a deep-water overflow every year through the Luzon Strait, which is an important source of deep carbon cycling and nutrients in the South China Sea. And the water is also critical to the biogeochemical cycling processes in the South China Sea as an important lateral source of deep carbon cycling and nutrients.

Since 2009, the research team has been observing the deep-water overflow. Based on the statistics collected from 5 long-term fixed observation submersible stations located in key sea thresholds of Bashi Strait, Luzon Trough and Hengchun Ridge, the pre-study has shown that the spatial features, movement path and mean annual flow of the deep-water overflow had been given systematical description. The study also revealed the seasonal variability of the deep-water overflow and its mixed driving mechanism.

Based on 12 years of continuous flow data, the team revealed for the first time the inter-annual variability and continuous strengthening trend of deep-water overflow in the Luzon Strait. It shows that the flux of the deep-water overflow in the Luzon Strait has increased over the past 12 years and that the interannual increase in the pressure difference between the two sides is a key regulatory factor for the enhancement of the deep-water overflow.

The findings above enriched the understanding of the deep circulation in the Luzon Strait and the South China Sea, providing important insights into the position of the deep circulation between the two in the Pacific overturning circulation and global climate change. 

The research was funded by the National Natural Science Foundation of China and the National Key Research and Development Programme of China, and was also supported by the research vessel DFH-2.