Remotely sensed study of air-sea CO2 fluxes variability in the Northern South China Sea

The CO₂ source or sink status and variability in the coastal ocean are the subjects of highly debate. Satellite remote sensing offers an avenue for expanding observations and analyzing temporal and spatial variability of the environment of the ocean. In the present study, the algorithm for surface layer seawater partial pressure of CO₂ (pCO_2sw) of the northern South China Sea (NSCS) was applied to remote sensing products and the air-sea CO₂ fluxes were calculated from salinity, wind speed corrected to 10 meters, sea surface temperature data obtained from remote sensing in the NSCS, for the period 2004-2007. The CO₂ source and sink status in the NSCS were analysed and showed significant variability in time and space. In winter, the pCO_2sw in most of the NSCS ranged from ~320-360 ?atm, indicative of undersaturation with respect to atmospheric partial pressure of CO₂ (pCO_2air). However, in summer, the pCO_2sw increased to ~400-420 ?atm mainly due to sea surface temperature. The air-sea CO₂ fluxes in summer have been increasing year after year which have the same trend with the pCO_2sw. These upswings correlated with a rise in sea surface temperatures, showing that sea surface temperatures played key role in the CO₂ source and sink status in NSCS. In regions of the Luzon Strait, the air-sea CO₂ flux remained generally high likely associated with the remineralization of organic matter. The pCO_2sw highly undersaturation conditions occurred on the western part of the Taiwan Strait in winter, which may be caused by the low temperature and low salinity China coastal current entering the Taiwan Strait driven by the northeast monsoon. The research showed that most of the NSCS represents weak sinks for atmospheric CO₂ in winter and sources for atmospheric CO₂ in summer.