Seasonal variations of seawater p CO 2 and sea‐air CO 2 fluxes in a fringing coral reef, northern S outh C hina S ea

Evidence based on four field surveys conducted between July 2009 and April 2011 indicates that both sea surface partial pressures of CO 2 ( p CO 2 ) and sea–air CO 2 fluxes at Luhuitou fringing reef in Sanya, Hainan Island, northern South China Sea (SCS) are subject to significant seasonal variations. The diurnal variation of seawater p CO 2 ranges from 264 to 579 μ atm in summer, which is much larger than that in autumn (152–335 μ atm), in winter (84–260 μ atm), and in spring (114–228 μ atm). The sea‐air CO 2 flux in summer (∼9.6 mmol CO 2 m −2 d −1 ) is also larger than that in other seasons (i.e.,∼3 mmol CO 2 m −2 d −1 in spring, ∼3.5 mmol CO 2 m −2 d −1 in autumn, and ∼2.7 mmol CO 2 m −2 d −1 in winter). The atmospheric p CO 2 in this reef shows small diurnal and seasonal variations. The integration of the time‐series p CO 2 data shows that the reef area is a weak source of atmospheric CO 2 at ∼0.54 mol CO 2 m −2 yr −1 . Further analyses indicate that the seasonal variations of the surface seawater p CO 2 in Luhuitou fringing reef are mainly affected by seasonally‐dependent biological metabolic processes (organic processe and inorganic process), and that the organic process play a more important role than the inorganic process. Seasonal sea surface temperature (SST) variations and hydrodynamic processes may also have some influence on seawater p CO 2 variation.