Uncertainty in air–sea CO₂ flux due to transfer velocity

From TOPEX/Poseidon data, the significant uncertainty in global air–sea carbon dioxide (CO₂) flux in 2000 is calculated from 21 wind-speed-dependent and 5 sea-state-dependent CO₂ transfer velocities and the sea-to-air partial pressure difference [Inline formula] proposed by Takahashi, Sutherland, and Kozyr (2010). The sea-state-dependent parameterizations are calculated based on the significant wave height (SWH) and the radar backscatter coefficient [Inline formula] measured using the Ku-band altimeter. Uncertainty in air‐sea CO₂ flux is compared using 26 various transfer velocity formulas. The maximum differences in global monthly mean and 4° zonal mean values for gas transfer velocity among these formulas are 33.20 and 108.20 cm hour^‐1, respectively. The corresponding differences for sea-to-air CO₂ flux are 6.41 and 0.58 Pg C year^‐1, respectively. Monthly mean global maps of gas transfer velocity and flux are also presented. The average value of the global mean, transfer velocity obtained using the 26 formula is 27.33 ± 9.75 cm hour^‐1, and the averaged total global net air-to-sea CO₂ flux is 2.77 ± 1.02 Pg C year^‐1 after area weighting and Schmidt number correction. The sea-state-dependent parameterizations are near these values, providing a successful method to estimate the air‐sea CO₂ transfer velocity and flux.