Upper-ocean gas dynamics from radon profiles in the Eastern Tropical South Pacific

Uncertainties in the dynamics of dissolved gases limit the accuracy of geochemical primary-productivity estimates. Mixed-layer ventilation, entrainment, and upwelling all affect the interpretation of geochemical data, yet they are rarely measured together. We report upper-ocean dissolved-gas dynamics in the Eastern Tropical South Pacific (10-20°S, 80-100°W) obtained from 222Rn distributions from a research cruise in February 2010. Radon-222-based surface ventilation measurements at seven stations were compared with gas transfer velocities calculated using empirical wind-speed parameterizations. Good agreement between the two methods was observed across different wind data products (ASCAT scatterometer and NCEP/NCAR meterological reanalysis) and grid scales (0.5°×0.5°, 1°×1°, and 2°×2°). Average wind speeds in the region were 5-8 m s−1, corresponding to in situ gas transfer velocities of 1-3 m d−1. Averaged over the region, most recent gas exchange parameterizations performed similarly, and the results are robust with respect to both wind data products and grid scales. Non-steady-state conditions were observed at one station, possibly caused by a recent internal wave. These results suggest that 222Rn could be used to support measurements of biogeochemical O2 and CO2 fluxes in the upper ocean.