Preliminary and novel estimates of CO₂gas transfer using a satellite scatterometer during the 2001GasEx experiment

The ocean takes up approximately 30% of the annual anthropogenic emissions of CO2. However, the air–sea exchange of carbon dioxide varies by a factor of 2 depending on the formulation of the exchange process. This considerable uncertainty is due in part to the difficulty in parameterizing the gas transfer velocity, k 660, usually given as a function of wind speed. Recent field data showed that parametrization using the mean square slope of small scale surface waves provides a more robust strategy to estimate gas transfer (Frew et al. 2004 Frew, N., Bock, E., Schimpf, U., Hara, T., Haußecker, H., Edson, J., McGillis, W., Nelson, R., McKenna, S.Uz, B. 2004. Air–sea gas transfer: Its dependence on wind stress, small-scale roughness, and surface films. Journal of Geophysical Research, 109 doi: 10.1029 2003JC002131[Crossref] , [Google Scholar]). Here we present a preliminary estimation of the gas transfer velocity as a function of upwind Normalized Radar Cross-Section (NRCS) as measured by the scatterometer QuikSCAT. The gas transfer velocity calculated from upwind NRCS exhibits a quadratic-like dependence at low and intermediate wind speeds (≃6 ms–1 ). This approach represents a promising new tool to obtain global quasi-synoptic estimates of oceanic uptake of CO2.