Continuous measurements of methane mixing ratios from ice cores

Stowasser, C.; Buizert, Christo; Gkinis, Vasileios; Chappellaz, J.; Schüpbach, Simon; Bigler, Matthias; Faïn, Xavier; Sperlich, Peter; Baumgartner, Michael F.; Schilt, A.; Blunier, Thomas

doi:10.5194/amtd-5-211-2012

Cited by 11 publications

(13 citation statements)

References 34 publications

(22 reference statements)

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“…In addition to discrete CH 4 samples, we also measured CH 4 simultaneously with trace element analysis using a continuous technique [ Rhodes et al ., ; Stowasser et al ., ]. The samples for this analysis were smaller (3 × 3 × 22 cm) than has been typically used (3.4 × 3.4 × 55 cm), yet this provides a unique opportunity to compare the continuous technique to discrete measurements on samples within the LIZ.…”

Section: Methodsmentioning

confidence: 99%

Observing and modeling the influence of layering on bubble trapping in polar firn

et al. 2015

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Interpretation of ice core trace gas records depends on an accurate understanding of the processes that smooth the atmospheric signal in the firn. Much work has been done to understand the processes affecting air transport in the open pores of the firn, but a paucity of data from air trapped in bubbles in the firn-ice transition region has limited the ability to constrain the effect of bubble closure processes. Here we present high-resolution measurements of firn density, methane concentrations, nitrogen isotopes, and total air content that show layering in the firn-ice transition region at the West Antarctic Ice Sheet (WAIS) Divide ice core site. Using the notion that bubble trapping is a stochastic process, we derive a new parameterization for closed porosity that incorporates the effects of layering in a steady state firn modeling approach. We include the process of bubble trapping into an open-porosity firn air transport model and obtain a good fit to the firn core data. We find that layering broadens the depth range over which bubbles are trapped, widens the modeled gas age distribution of air in closed bubbles, reduces the mean gas age of air in closed bubbles, and introduces stratigraphic irregularities in the gas age scale that have a peak-to-peak variability of~10 years at WAIS Divide. For a more complete understanding of gas occlusion and its impact on ice core records, we suggest that this experiment be repeated at sites climatically different from WAIS Divide, for example, on the East Antarctic plateau.

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Section: Methodsmentioning

confidence: 99%

Observing and modeling the influence of layering on bubble trapping in polar firn

et al. 2015

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“…To change the data resolution of a commercial analyzer, the simplest approach is to change the flow rate through the cavity. This approach has been used when limited air samples are available [ Stowasser et al , ]. To minimize the damping of the ambient signal by the inlet tubing, the ratio between the inside surface area and the airflow volume should be minimized.…”

Section: Techniques Of Measurementmentioning

confidence: 99%

Stable isotopes in atmospheric water vapor and applications to the hydrologic cycle

Galewsky

Steen‐Larsen

Field

et al. 2016

Reviews of Geophysics

313

314

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The measurement and simulation of water vapor isotopic composition has matured rapidly over the last decade, with long‐term data sets and comprehensive modeling capabilities now available. Theories for water vapor isotopic composition have been developed by extending the theories that have been used for the isotopic composition of precipitation to include a more nuanced understanding of evaporation, large‐scale mixing, deep convection, and kinetic fractionation. The technologies for in situ and remote sensing measurements of water vapor isotopic composition have developed especially rapidly over the last decade, with discrete water vapor sampling methods, based on mass spectroscopy, giving way to laser spectroscopic methods and satellite‐ and ground‐based infrared absorption techniques. The simulation of water vapor isotopic composition has evolved from General Circulation Model (GCM) methods for simulating precipitation isotopic composition to sophisticated isotope‐enabled microphysics schemes using higher‐order moments for water and ice size distributions. The incorporation of isotopes into GCMs has enabled more detailed diagnostics of the water cycle and has led to improvements in its simulation. The combination of improved measurement and modeling of water vapor isotopic composition opens the door to new advances in our understanding of the atmospheric water cycle, in processes ranging from the marine boundary layer, through deep convection and tropospheric mixing, and into the water cycle of the stratosphere. Finally, studies of the processes governing modern water vapor isotopic composition provide an improved framework for the interpretation of paleoclimate proxy records of the hydrological cycle.

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“…Additionally, ice core CH 4 records allow us to investigate how CH 4 variability at the centennial‐scale interacts with major climatic transitions, such as glacial‐interglacial cycles. Ice core CH 4 data of sufficiently high temporal resolution and level of precision have become available recently due to analytical advances utilizing laser spectroscopy [ Stowasser et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Atmospheric methane variability: Centennial‐scale signals in the Last Glacial Period

Rhodes

Brook

McConnell

et al. 2017

Global Biogeochemical Cycles

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In order to understand atmospheric methane (CH 4 ) biogeochemistry now and in the future, we must apprehend its natural variability, without anthropogenic influence. Samples of ancient air trapped within ice cores provide the means to do this. Here we analyze the ultrahigh-resolution CH 4 record of the West Antarctic Ice Sheet Divide ice core 67.2-9.8 ka and find novel, atmospheric CH 4 variability at centennial time scales throughout the record. This signal is characterized by recurrence intervals within a broad 80-500 year range, but we find that age-scale uncertainties complicate the possible isolation of any periodic frequency. Lower signal amplitudes in the Last Glacial relative to the Holocene may be related to incongruent effects of firn-based signal smoothing processes. Within interstadial and stadial periods, the peak-to-peak signal amplitudes vary in proportion to the underlying millennial-scale oscillations in CH 4 concentration-the relative amplitude change is constant. We propose that the centennial CH 4 signal is related to tropical climate variability that influences predominantly low-latitude wetland CH 4 emissions.Plain Language Summary Using a new method to measure methane concentrations of ancient air trapped in ice cores, we have detected variability in atmospheric methane concentration on centennial time scales in the Last Glacial Period for the first time. We know these signals represent past changes in atmospheric methane because they appear in several ice core records. We propose that changes in methane emissions from tropical wetlands are responsible. How this new variability might be related to similar signals found in the late Holocene ice core records and the instrumental record of atmospheric methane is an open question.

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Continuous measurements of methane mixing ratios from ice cores

Cited by 11 publications

References 34 publications

Observing and modeling the influence of layering on bubble trapping in polar firn

Observing and modeling the influence of layering on bubble trapping in polar firn

Stable isotopes in atmospheric water vapor and applications to the hydrologic cycle

Atmospheric methane variability: Centennial‐scale signals in the Last Glacial Period

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