| Air-sea CO2flux is one of the most important control factors on the global climate change,and is one of the hot spots of the international research. Based on a substantial amount ofliterature on air-sea CO2transfer velocity and its environmental controls, it has been concludedthat CO2transfer velocity is not only infected by the wind speed, but also related to the wave,thickness of the mixed layer and the atmospheric stratification. The thickness of the boundarylayer is a function of surface turbulent and diffusion coefficient and it is also affected by windspeed, fetch, wave age, wave steepness, whitecap, stability of the boundary layer and surfactant.In this paper, a study on the inversion algorithms of air-sea CO2transfer velocity and flux fromsatellite data was carried out. Based on altimeter and scatterometer data, uncertainty of the CO2transfer velocity and flux, the effects of the breaking and non-broken waves to CO2transfervelocity and the effects of the wave steepness are investigated. The main results are followed:（1） A new formula to retrieve air friction velocity using altimeter data was proposed. Usingdata from TOPEX/Poseidon for the entire year of2000and26different transfer velocityformulas, uncertainties in CO2transfer velocity and flux were estimated. There are largeuncertainties in estimating CO2transfer velocity and flux due to various transfer velocities.Maximum differences of global monthly mean values are27.70cm h-1and6.41Pg C year-1forgas transfer velocities and sea-air CO2fluxes respectively among these26formulas. Maximumdifferences of4°zonal mean values are70.37cm h-1and0.58Pg C year-1for CO2transfervelocities and sea-air CO2flux respectively among these26formulas. The average global meanvalue for CO2gas transfer velocities is27.33±9.75cm h-1, and the average total global netair-to-sea CO2is2.77±1.02Pg C year-1after area weighting and Schmidt number correction.（2） Using a function of radar backscatter coefficient from Ku-band altimeter, significantwave height （SWH） and wind speed, the global, long time series air-sea CO2transfer velocitywas calculated. Both the wind speed and wave state were taking into account. Globaldistributions and seasonal distributions of the air-sea CO2transfer velocity were retrieved anddiscussed. The19-year increase rate of the air-sea transfer velocity was about0.01cm h-1per month. The19-year averaged global, area-weighted, Schmidt number-corrected mean gastransfer velocity was36.14±1.62cm h-1.（3） A new formula to retrieve CO2transfer velocity using altimeter data was proposed.This formula distinguished the contributions of the wave breaking part and non-broken part totransfer velocity using whitecaps coverage. Global distributions and seasonal distributions of theair-sea CO2transfer velocity and flux were retrieved from TOPEX/Poseidon and Jason altimeterdata from October1992to December2009using the combined algorithm. The increase rate ofthe air-sea transfer velocity and flux was about0.725cm h-1per year and0.266PgC per year,respectively. The17-year averaged gobal, area-weighted, Schmidt number-corrected mean gastransfer velocity was21.26cm h-1. Average total CO2flux from atmosphere to ocean during the17years was2.58PgC per year.（4） Using the European Remote Sensing scatterometer （ERS-2） data from July1997toAugust1998, a new model of air-sea CO2transfer velocity with surface wind speed and wavesteepness is proposed. Wave steepness （δ） was retrieved using a Neural Network （NN） modelfrom ERS-2scatterometer data, while the wind speed was directly derived by the ERS-2scatterometer. The new model agrees well with the formulations based on wind speed and thevariation in the wind speed dependent relationships presented in many previous studies can beexplained by this proposed relation with variation in wave steepness effect. This methodreflected the impact of the different wave fields to the CO2transfer velocity and flux andexplained the reason of the uncertainty partly. Seasonally global maps of gas transfer velocityand flux were shown based on the new model and seasonal variations of the transfer velocity andflux during the1-year period were illustrated. The global mean gas transfer velocity is30cm h-1after area-weighting and Schmidt number correction, while the total air to sea CO2flux in thatyear was1.77PgC. |
