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Bacterioneuston control of air‐water methane exchange determined with a laboratory gas exchange tank
Author(s) -
UpstillGoddard Robert C.,
Frost Thomas,
Henry Gordon R.,
Franklin Mark,
Murrell J. Colin,
Owens Nicholas J. P.
Publication year - 2003
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2003gb002043
Subject(s) - methanotroph , methane , gas chromatography , seawater , chemistry , hydrocarbon , analytical chemistry (journal) , environmental chemistry , pulmonary surfactant , chromatography , anaerobic oxidation of methane , ecology , biology , biochemistry , organic chemistry
The apparent transfer velocities ( k w ) of CH 4 , N 2 O, and SF 6 were determined for gas invasion and evasion in a closed laboratory exchange tank. Tank water (pure Milli‐RO® water or artificial seawater prepared in Milli‐RO®) and/or tank air gas compositions were adjusted, with monitoring of subsequent gas transfer by gas chromatography. Derived k w was converted to “apparent k 600 ,” the value for CO 2 in freshwater at 20°C. For CH 4 , analytical constraints precluded estimating apparent k 600 based on tank air measurements. In some experiments we added strains of live methanotrophs. In others we added chemically deactivated methanotrophs, non‐CH 4 oxidizers ( Vibrio ), or bacterially associated surfactants, as controls. For all individual controls, apparent k 600 estimated from CH 4 , N 2 O, or SF 6 was indistinguishable. However, invasive estimates always exceeded evasive estimates, implying some control of gas invasion by bubbles. Estimates of apparent k 600 differed significantly between methanotroph strains, possibly reflecting species‐specific surfactant release. For individual strains during gas invasion, apparent k 600 estimated from CH 4 , N 2 O, or SF 6 was indistinguishable, whereas during gas evasion, k 600 ‐CH 4 was significantly higher than either k 600 ‐N 2 O or k 600 ‐SF 6 , which were identical. Hence evasive k 600 ‐CH 4 / k 600 ‐SF 6 was always significantly above unity, whereas invasive k 600 ‐CH 4 / k 600 ‐SF 6 was not significantly different from unity. Similarly, k 600 ‐CH 4 / k 600 ‐SF 6 for the controls and k 600 ‐N 2 O/ k 600 ‐SF 6 for all experiments did not differ significantly from unity. Our results are consistent with active metabolic control of CH 4 exchange by added methanotrophs in the tank microlayer, giving enhancements of ∼12 ± 10% for k 600 ‐CH 4 . Hence reactive trace gas fluxes determined by conventional tracer methods at sea may be in error, prompting a need for detailed study of the role of the sea surface microlayer in gas exchange.