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

Lookup NU author(s): Dr Klaus Schneider-Zapp, Dr Matthew Salter, Professor Robert Upstill-Goddard

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

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 normalisedkw estimates show close agreement. Repeated experiments with MilliQ 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.


Publication metadata

Author(s): Schneider-Zapp K, Salter ME, Upstill-Goddard RC

Publication type: Article

Publication status: Published

Journal: Ocean Science

Year: 2014

Volume: 10

Pages: 587-600

Print publication date: 03/07/2014

Online publication date: 03/07/2014

Acceptance date: 24/05/2014

ISSN (print): 1812-0784

ISSN (electronic): 1812-0792

Publisher: Copernicus Publications

URL: http://dx.doi.org/10.5194/os-10-587-2014

DOI: 10.5194/os-10-587-2014


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