Kinetic isotopic fractionation during air‐water gas transfer of O2, N2, CH4, and H2

Knox, Molly; Quay, Paul D.; Wilbur, David

doi:10.1029/92jc00949

Cited by 156 publications

(140 citation statements)

References 29 publications

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“…5b-d. It appears that a stronger fractionation during gas invasion of 18 ε I = −8 ‰ may lead to better agreement between s calc and s bio , but this 18 ε I value disagrees with the measured value of (−2.8 ± 0.2) ‰ (Knox et al, 1992 oxygen production rates. Clearly, in addition to allowing a more consistent calculation of g (Sect.…”

Section: Practical Example: Calculation Of G Values In the Southern Ocontrasting

confidence: 39%

“…6.1 how the derived g values would change for 17 P = 150 ppm. 18 ε I , 17 ε I , 18 ε E , 17 ε E The kinetic isotope fractionation during O 2 invasion was measured as 18 ε I = (−2.8 ± 0.2) ‰ (Knox et al, 1992). I am not aware of any triple oxygen isotope studies of the corresponding 17 O/ 16 O isotope fractionation and therefore adopt 17 ε I = (1 + 18 ε I ) θ -1, with θ = 0.516 ± 0.015, covering the theoretically predicted range for mass-dependent isotope effects (Kaiser, 2008).…”

Section: Photosynthesismentioning

confidence: 99%

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Technical note: Consistent calculation of aquatic gross production from oxygen triple isotope measurements

Kaiser

2011

Biogeosciences

144

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Abstract. Oxygen triple isotope measurements can be used to calculate aquatic gross oxygen production rates. Past studies have emphasised the appropriate definition of the 17 O excess and often used an approximation to derive production rates from the 17 O excess. Here, I show that the calculation can be phrased more consistently and without any approximations using the relative 17 O/ 16 O and 18 O/ 16 O isotope ratio differences (delta values) directly. I call this the "dual delta method". The 17 O excess is merely a mathematical construct and the derived production rate is independent of its definition, provided all calculations are performed with a consistent definition. I focus on the mixed layer, but also show how time series of triple isotope measurements below the mixed layer can be used to derive gross production.In the calculation of mixed layer productivity, I explicitly include isotopic fractionation during gas invasion and evasion, which requires the oxygen supersaturation s to be measured as well. I also suggest how bubble injection could be considered in the same mathematical framework. I distinguish between concentration steady state and isotopic steady state and show that only the latter needs to be assumed in the calculation. It is even possible to derive an estimate of the net production rate in the mixed layer that is independent of the assumption of concentration steady state.I review measurements of the parameters required for the calculation of gross production rates and show how their systematic uncertainties as well as the use of different published calculation methods can cause large variations in the production rates for the same underlying isotope ratios. In particular, the 17 O excess of dissolved O 2 in equilibrium with atmospheric O 2 and the 17 O excess of photosynthetic O 2 need to be re-measured. Because of these uncertainties, all calculaCorrespondence to: J. Kaiser (j.kaiser@uea.ac.uk) tion parameters should always be fully documented and the measured relative isotope ratio differences as well as the oxygen supersaturation should be permanently archived, so that improved measurements of the calculation parameters can be used to retrospectively improve production rates.

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Section: Practical Example: Calculation Of G Values In the Southern Ocontrasting

confidence: 39%

Section: Photosynthesismentioning

confidence: 99%

Technical note: Consistent calculation of aquatic gross production from oxygen triple isotope measurements

Kaiser

2011

Biogeosciences

144

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“…Literature-derived values of a were used for both loss pathways. For evasion, an a value of 0.9992 was used 66 , and for MOX, the range reported by Bastviken et al 62 (0.9816-0.9792) was used.…”

Section: Methodsmentioning

confidence: 99%

Oxic water column methanogenesis as a major component of aquatic CH4 fluxes

et al. 2014

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Methanogenesis has traditionally been assumed to occur only in anoxic environments, yet there is mounting, albeit indirect, evidence of methane (CH 4 ) production in oxic marine and freshwaters. Here we present the first direct, ecosystem-scale demonstration of methanogenesis in oxic lake waters. This methanogenesis appears to be driven by acetoclastic production, and is closely linked to algal dynamics. We show that oxic water methanogenesis is a significant component of the overall CH 4 budget in a small, shallow lake, and provide evidence that this pathway may be the main CH 4 source in large, deep lakes and open oceans. Our results challenge the current global understanding of aquatic CH 4 dynamics, and suggest a hitherto unestablished link between pelagic CH 4 emissions and surface-water primary production. This link may be particularly sensitive to widespread and increasing human influences on aquatic ecosystem primary productivity.

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“…The magnitudes of al and la are known (Ϫ2.8 and Ϫ3.5‰, respectively; Knox et al 1990); ␦ 18 O w , ␦ 18 O diss , and GP( 18 O) were determined experimentally; and R epi and I were calculated as discussed below. The rate of O 2 uptake in the epilimnion (R epi ) can be determined from the difference between gross production and net air-lake O 2 flux due to biological forcing alone (NF).…”

Section: Evaluation Of the Significance Of O 2 Uptake Mechanisms-mentioning

confidence: 99%

Evaluation of community respiratory mechanisms with oxygen isotopes: A case study in Lake Kinneret

Luz

Barkan

Sagi

et al. 2002

Limnology & Oceanography

125

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Gross and net O 2 production between May 1996 and February 1999 was determined in bottle incubation experiments with H 2 18 O spike and from the change in O 2 concentration. Carbon fixation rates were obtained from 14 C incubations. In general, production rates determined using the H 2 18 O-spike were about twice the primary production determined by the 14 C method, where the latter was close to net oxygen evolution. These relationships are similar to results for the open ocean. During the spring bloom, when the dinoflagellate Peridinium was abundant, the ratio of gross O 2 production to carbon fixation was about 7.5, and net O 2 production was greater than carbon fixation. The difference between O 2 gross production and carbon fixation results, at least in part, from uptake by Mehler reaction and from recycling of the 14 C tracer by dark respiration and the alternative oxidase (AOX). We used the difference in isotopic discrimination against 18 O, occurring during O 2 consumption by various biological pathways, to place constraints on the relative engagement of these pathways. We estimated the overall discrimination against 18 O in the lake from O 2 isotopic mass balance as 20.5-29‰. The only mechanism that can explain the strong overall fractionation in the lake is AOX, which strongly discriminates against 18 O (ϳ31‰). Our results show, for the first time, that uptake by AOX is widespread and quantitatively important to oxygen consumption in aquatic systems.Oxygen exchange by photosynthesis and respiration is the largest biogeochemical cycle in aquatic systems. In order to understand this cycle, it is necessary to know the gross rates of the major processes involved in oxygen production and uptake. Production of O 2 is known to occur in one process in photosystem II, but O 2 consumption in aquatic organisms is possible by several reactions. These include ordinary respiration through the cytochrome oxidase pathway, respiration by the alternative oxidase pathway, Mehler reaction, and photorespiration. The first two processes take place in light as well as in dark conditions, whereas the latter two occur only under illumination. Although the presence of the above mechanisms has been established in different studies, their quantitative importance in the overall O 2 uptake in aquatic systems is not well known, and it is necessary to assess their role in natural environments. In this respect, ordinary O 2 incubation methods, which are very useful for the assessment of photosynthetic production from light-and dark-incubation experiments (e.g., Williams and Purdie 1991), do not provide the necessary information. The main drawback of these methods is their inability to measure the rate of O 2 AcknowledgmentsWe thank Y. Geiffman and the Mekorot Watershed Unit for provision of wind data and extend special thanks to the Kinneret Limnological Laboratory skipper M. Hatab. We are grateful

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Kinetic isotopic fractionation during air‐water gas transfer of O₂, N₂, CH₄, and H₂

Cited by 156 publications

References 29 publications

Technical note: Consistent calculation of aquatic gross production from oxygen triple isotope measurements

Technical note: Consistent calculation of aquatic gross production from oxygen triple isotope measurements

Oxic water column methanogenesis as a major component of aquatic CH4 fluxes

Evaluation of community respiratory mechanisms with oxygen isotopes: A case study in Lake Kinneret

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