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Southern Ocean Gas Exchange Experiment: Setting the stage

[1] The Southern Ocean Gas Exchange Experiment (SO GasEx) is the third in a series of
U.S.‐led open ocean process studies aimed at improving the quantification of gas transfer
velocities and air‐sea CO2 fluxes. Two deliberate 3He/SF6 tracer releases into relatively
stable water masses selected for large DpCO2 took place in the southwest Atlantic sector
of the Southern Ocean in austral fall of 2008. The tracer patches were sampled in a
Lagrangian manner, using observations from discrete CTD/Rosette casts, continuous
surface ocean and atmospheric monitoring, and autonomous drifting instruments to study
the evolution of chemical and biological properties over the course of the experiment. CO2
and DMS fluxes were directly measured in the marine air boundary layer with
micrometeorological techniques, and physical, chemical, and biological processes
controlling air‐sea fluxes were quantified with measurements in the upper ocean and
marine air. Average wind speeds of 9 m s−1 to a maximum of 16 m s−1 were encountered
during the tracer patch observations, providing additional data to constrain wind speed/gas
exchange parameterizations. In this paper, we set the stage for the experiment by detailing
the hydrographic observations during the site surveys and tracer patch occupations that
form the underpinning of observations presented in the SO GasEx special section.
Particular consideration is given to the mixed layer depth as this is a critical variable for
estimates of fluxes and biogeochemical transformations based on mixed layer budgets.