Seasonal variations of seawater pCO2 and sea-air CO2 fluxes in a fringing coral reef, northern South China Sea
Hongqiang Yan1, Kefu Yu1,2, Qi Shi1, Yehui Tan1, Guohui Liu1, Meixia Zhao1, Shu Li1, Tianran Chen1, and Yinghui Wang2
1Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China, 2Coral Reef Research Center of China, Guangxi University, Nanning, China
Abstract Evidence based on four ﬁeld surveys conducted between July 2009 and April 2011 indicates that both sea surface partial pressures of CO2 (pCO2) and sea–air CO2 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 pCO2 ranges from 264 to 579 latm in summer, which is much larger than that in autumn (152–335 latm), in winter (84–260 latm), and in spring (114–228 latm). The sea-air CO2 ﬂux in summer (9.6 mmol CO2 m22 d21) is also larger than that in other seasons (i.e.,3 mmol CO2 m22 d21 in spring,3.5 mmol CO2 m22 d21 in autumn, and2.7 mmol CO2 m22 d21 in winter). The atmospheric pCO2 in this reef shows small diurnal and seasonal variations. The integration of the time-series pCO2 data shows that the reef area is a weak source of atmospheric CO2 at0.54 mol CO2 m22 yr21. Further analyses indicate that the seasonal variations of the surface seawater pCO2 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 pCO2 variation.
Yan et al coral reef CO2-JGR .pdf