Comment on “Measurements of air‐sea gas exchange at high wind speeds in the Southern Ocean: Implications for global parameterizations” by D. T. Ho et al.

Abstract

[1] Recently, Ho et al. [2006] presented the gas transfer velocity measurements at high wind speeds from the SOLAS New Zealand Air-Sea Exchange (NZ-SAGE) experiment conducted in the western Pacific sector of Southern Ocean. Gas transfer velocities were determined using the He/SF6 dual gas tracer technique. The NZ-SAGE experiment alone has more than doubled the number of He/SF6-derived gas transfer velocity measurements from the open ocean, and the measurements spread into high wind speed range (above 10 m s ), which is extremely useful in determining empirical parameterizations of gas transfer velocity. One of the conclusions from the paper is that ‘‘The results clearly reveal a quadratic relationship between wind speed and gas transfer velocity, rather than a recently proposed cubic relationship.’’ While we congratulated their significant success in collecting gas transfer velocity measurements at high wind speeds through the NZSAGE experiment, we would like to point out that one of the assumptions implied in the data presentation, namely the form of enhancement factor, e, that was adopted, favors the quadratic relationship between wind speed and gas transfer velocity. Therefore the above conclusion is less convincing, and we also fear that hasty readers could get the wrong impression when comparing gas transfer velocity measured at different timescales. This is of great importance to the outcomes of data-fitting parameterizations that are currently employed in estimating air-sea CO2 fluxes and in climate models for study of CO2 cycles.