Preliminary and novel estimates of CO₂ gas transfer using a satellite scatterometer during the 2001GasEx experiment

Abstract

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). 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.

Acknowledgments

We are grateful to Mark Donelan for his helpful comments. We thank anonymous reviewers for thorough comments on a previous version of this manuscript. WD acknowledges support from NOAA-OGP, grant number NA17RJ1223 and the assistance of Mike Rebozo, Joe Gabriele, and numerous GasEx investigators. DB, MEC, PW, and MS acknowledge the support of the NASA Ocean Biogeochemistry program. Part of this work was carried out at the Jet Propulsion Laboratory under contract with the National Aeronautics and Space Administration. TH acknowledges the support of NOAA CPO/GCC.