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Ocean Science An interactive open-access journal of the European Geosciences Union
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Volume 10, issue 4
Ocean Sci., 10, 587–600, 2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ocean Sci., 10, 587–600, 2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 03 Jul 2014

Research article | 03 Jul 2014

An automated gas exchange tank for determining gas transfer velocities in natural seawater samples

K. Schneider-Zapp1, M. E. Salter2, and R. C. Upstill-Goddard1 K. Schneider-Zapp et al.
  • 1Ocean Research Group, School of Marine Science and Technology, Newcastle University, Newcastle upon Tyne, UK
  • 2Department of Applied Environmental Science, Stockholm University, Stockholm, Sweden

Abstract. In order to advance understanding of the role of seawater surfactants in the air–sea exchange of climatically active trace gases via suppression of the gas transfer velocity (kw), we constructed a fully automated, closed air–water gas exchange tank and coupled analytical system. The system allows water-side turbulence in the tank to be precisely controlled with an electronically operated baffle. Two coupled gas chromatographs and an integral equilibrator, connected to the tank in a continuous gas-tight system, allow temporal changes in the partial pressures of SF6, CH4 and N2O to be measured simultaneously in the tank water and headspace at multiple turbulence settings, during a typical experimental run of 3.25 h. PC software developed by the authors controls all operations and data acquisition, enabling the optimisation of experimental conditions with high reproducibility. The use of three gases allows three independent estimates of kw for each turbulence setting; these values are subsequently normalised to a constant Schmidt number for direct comparison. The normalised kw estimates show close agreement. Repeated experiments with Milli-Q water demonstrate a typical measurement accuracy of 4% for kw. Experiments with natural seawater show that the system clearly resolves the effects on kw of spatial and temporal trends in natural surfactant activity. The system is an effective tool with which to probe the relationships between kw, surfactant activity and biogeochemical indices of primary productivity, and should assist in providing valuable new insights into the air–sea gas exchange process.

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