Sub-month processes contribute significantly to CO₂ uptakes in the South China Sea

Estimating multi-year average air-sea CO₂ flux over a large area usually uses monthly mean variables from the atmosphere and ocean. Ignoring sub-monthly processes will blur the oceanic carbon cycle, especially when the synoptical and sub-seasonal scale processes are significant, like the South China Sea (SCS). Based on an empirical relationship between <i>p_CO2w</i> and sea surface temperature (<i>SST</i>), we re-calculated the air-sea CO₂ flux of the SCS with daily products of atmospheric reanalysis and <i>SST</i>. Our results show that the sub-monthly process contributes 10% of the total CO₂ flux of SCS and can even alter the sign of the CO₂ flux in the spring. In the near-surface coupling process, intra-monthly variations in surface winds play the dominant role, except in regions with significant ocean eddies. The co-spectrum analysis of <i>SST </i>and wind speed reveals the most essential oscillation of >20 days. Therefore, a product of the sea surface environment for 10-day intervals can better estimate the air-sea CO₂ flux over SCS than monthly data