Abstract: Based upon surveys conducted in August and September 2011, the distribution characteristics of aragonite saturation state (Ω_arag) were investigated in the Northern South China Sea.Based on a two end-member mixing model, the contributions to Ω_arag from two processes associated with upwelling:physical transport vs.biological production were analyzed.Results showed that transect A off the Pearl estuary was influenced by upwelling, while transect B off the Hainan Island was highly stratified.Ω_arag ranged from 1.87~3.05 along transect A and 1.77~3.29 along transect B.Low Ω_arag values primarily occurred in the upwelling area along transect A and deep water along transect B.Using a two end-member mixing model, we found that physical transport induced a Ω_arag decrease of up to 0.37.Aerobic respiration in the nearshore area caused Ω_arag to decrease by up to 0.7, while in the offshore area, biological production caused Ω_arag to increase by 0.1.In contrast, excess CO₂ derived from aerobic respiration in the deep water contributed to low Ω_arag along transect B.