It is still an open question on where a coastal upwelling system is a sink or source to the atmospheric CO2 due to the complexity of physical and biological regimes associated with upwelling.This study is sought to examine the air-sea CO2 fluxes and their controls in a coastal region affected by wind-driven and topographic upwelling in the Southern Taiwan Strait.Field measurements were undertaken through three transects in July-August 2004,July 2005 and in June-July 2006.During all the three cruises,we observed different stages of upwelling development,e.g.,prior upwelling regime,upwelling peaks and its relaxation.The relationship between the Dissolved Inorganic Carbon (DIC) and Total Alkalinity (TA) suggests that there are three end members of water masses,ie.,coastal water,Northern South China Sea (NSCS) surface water and Deep NSCS water,and that physical mixing largely controls the offshore areas.At the same time the inshore area was dominated by high temperature,low salinity freshwater until the upwelling event developed,when the front between coastal water and upwelling water became biologically productive due to the enhanced nutrient supplies by upwelling.This enhancement of productivity also lowered the pCO2.