Coupled circulation and ecosystem trends in the South China Sea: response to changing climate

The ocean circulation in the South China Sea (SCS) is controlled by wind-driven ocean circulation in the basin and by mass flux through the straits that are linked with adjacent seas. The ecosystem of the SCS is governed physically by intrusion/extrusion of nutrients in the water column via the straits and bio-geochemically by the nutrient cycle through food web dynamics in the upper SCS. The ecosystem of the SCS and circulation are closely coupled, particularly in their long-term trends. Based on results from a future 100-year simulation using China Sea Multi-scale Ocean Modeling System (CMOMS) of coupled physics-biogeochemistry, which are validated by the available measurements and scientific understandings at the present time, we investigated the responses of ocean circulation and biogeochemical process to the changing climate in both the basin and adjacent seas and elaborated the coupled circulation and ecosystem trends in the SCS. We found that as result of the changing atmospheric forcing, Norther Equatorial Current and thus Kuroshio in the West Pacific Ocean (WPO) strengthen, which weakens the mass and nutrient transports into the SCS via Luzon Strait. The ocean circulations in both SCS and WPO are more sensitivity to the change of atmospheric heat flux and less sensitive to the change in atmospheric circulation. The spatially heterogeneous atmospheric heating to the ocean is attributed to the ocean circulation and transport changes in the WPO and SCS. The ecosystem trend is primarily controlled by the input/output of nutrients by the transport crossing the straits around the SCS, rather than by the biogeochemical processes in the upper SCS. The biological productivity has a weakening trend in the SCS as a result of the reduction of nutrient fluxes through the deep Luzon Strait and the enhancement of water column stability.