Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements?
Methane is a strong greenhouse gas and large uncertainties exist concerning the future evolution of its atmospheric abundance. Analyzing methane atmospheric mixing and stable isotope ratios in air trapped in polar ice sheets helps in reconstructing the evolution of its sources and sinks in the past....
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ftuniveastangl:oai:ueaeprints.uea.ac.uk:53682 2023-05-15T16:39:20+02:00 Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements? Sapart, C. J. Martinerie, P. Witrant, E. Chappellaz, J. van de Wal, R. S. W. Sperlich, P. van der Veen, C. Bernard, S. Sturges, W. T. Blunier, T. Schwander, J. Etheridge, D. Röckmann, T. 2013-07-24 https://ueaeprints.uea.ac.uk/id/eprint/53682/ https://doi.org/10.5194/acp-13-6993-2013 unknown Sapart, C. J., Martinerie, P., Witrant, E., Chappellaz, J., van de Wal, R. S. W., Sperlich, P., van der Veen, C., Bernard, S., Sturges, W. T., Blunier, T., Schwander, J., Etheridge, D. and Röckmann, T. (2013) Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements? Atmospheric Chemistry and Physics, 13 (14). pp. 6993-7005. ISSN 1680-7324 doi:10.5194/acp-13-6993-2013 Article PeerReviewed 2013 ftuniveastangl https://doi.org/10.5194/acp-13-6993-2013 2023-01-30T21:41:03Z Methane is a strong greenhouse gas and large uncertainties exist concerning the future evolution of its atmospheric abundance. Analyzing methane atmospheric mixing and stable isotope ratios in air trapped in polar ice sheets helps in reconstructing the evolution of its sources and sinks in the past. This is important to improve predictions of atmospheric CH4 mixing ratios in the future under the influence of a changing climate. The aim of this study is to assess whether past atmospheric δ13C(CH4) variations can be reliably reconstructed from firn air measurements. Isotope reconstructions obtained with a state of the art firn model from different individual sites show unexpectedly large discrepancies and are mutually inconsistent. We show that small changes in the diffusivity profiles at individual sites lead to strong differences in the firn fractionation, which can explain a large part of these discrepancies. Using slightly modified diffusivities for some sites, and neglecting samples for which the firn fractionation signals are strongest, a combined multi-site inversion can be performed, which returns an isotope reconstruction that is consistent with firn data. However, the isotope trends are lower than what has been concluded from Southern Hemisphere (SH) archived air samples and high-accumulation ice core data. We conclude that with the current datasets and understanding of firn air transport, a high precision reconstruction of δ13C of CH4 from firn air samples is not possible, because reconstructed atmospheric trends over the last 50 yr of 0.3–1.5 ‰ are of the same magnitude as inherent uncertainties in the method, which are the firn fractionation correction (up to ~2 ‰ at individual sites), the Kr isobaric interference (up to ~0.8 ‰, system dependent), inter-laboratory calibration offsets (~0.2 ‰) and uncertainties in past CH4 levels (~0.5 ‰). Article in Journal/Newspaper ice core University of East Anglia: UEA Digital Repository Atmospheric Chemistry and Physics 13 14 6993 7005 |
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Open Polar |
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University of East Anglia: UEA Digital Repository |
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ftuniveastangl |
language |
unknown |
description |
Methane is a strong greenhouse gas and large uncertainties exist concerning the future evolution of its atmospheric abundance. Analyzing methane atmospheric mixing and stable isotope ratios in air trapped in polar ice sheets helps in reconstructing the evolution of its sources and sinks in the past. This is important to improve predictions of atmospheric CH4 mixing ratios in the future under the influence of a changing climate. The aim of this study is to assess whether past atmospheric δ13C(CH4) variations can be reliably reconstructed from firn air measurements. Isotope reconstructions obtained with a state of the art firn model from different individual sites show unexpectedly large discrepancies and are mutually inconsistent. We show that small changes in the diffusivity profiles at individual sites lead to strong differences in the firn fractionation, which can explain a large part of these discrepancies. Using slightly modified diffusivities for some sites, and neglecting samples for which the firn fractionation signals are strongest, a combined multi-site inversion can be performed, which returns an isotope reconstruction that is consistent with firn data. However, the isotope trends are lower than what has been concluded from Southern Hemisphere (SH) archived air samples and high-accumulation ice core data. We conclude that with the current datasets and understanding of firn air transport, a high precision reconstruction of δ13C of CH4 from firn air samples is not possible, because reconstructed atmospheric trends over the last 50 yr of 0.3–1.5 ‰ are of the same magnitude as inherent uncertainties in the method, which are the firn fractionation correction (up to ~2 ‰ at individual sites), the Kr isobaric interference (up to ~0.8 ‰, system dependent), inter-laboratory calibration offsets (~0.2 ‰) and uncertainties in past CH4 levels (~0.5 ‰). |
format |
Article in Journal/Newspaper |
author |
Sapart, C. J. Martinerie, P. Witrant, E. Chappellaz, J. van de Wal, R. S. W. Sperlich, P. van der Veen, C. Bernard, S. Sturges, W. T. Blunier, T. Schwander, J. Etheridge, D. Röckmann, T. |
spellingShingle |
Sapart, C. J. Martinerie, P. Witrant, E. Chappellaz, J. van de Wal, R. S. W. Sperlich, P. van der Veen, C. Bernard, S. Sturges, W. T. Blunier, T. Schwander, J. Etheridge, D. Röckmann, T. Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements? |
author_facet |
Sapart, C. J. Martinerie, P. Witrant, E. Chappellaz, J. van de Wal, R. S. W. Sperlich, P. van der Veen, C. Bernard, S. Sturges, W. T. Blunier, T. Schwander, J. Etheridge, D. Röckmann, T. |
author_sort |
Sapart, C. J. |
title |
Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements? |
title_short |
Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements? |
title_full |
Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements? |
title_fullStr |
Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements? |
title_full_unstemmed |
Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements? |
title_sort |
can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements? |
publishDate |
2013 |
url |
https://ueaeprints.uea.ac.uk/id/eprint/53682/ https://doi.org/10.5194/acp-13-6993-2013 |
genre |
ice core |
genre_facet |
ice core |
op_relation |
Sapart, C. J., Martinerie, P., Witrant, E., Chappellaz, J., van de Wal, R. S. W., Sperlich, P., van der Veen, C., Bernard, S., Sturges, W. T., Blunier, T., Schwander, J., Etheridge, D. and Röckmann, T. (2013) Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements? Atmospheric Chemistry and Physics, 13 (14). pp. 6993-7005. ISSN 1680-7324 doi:10.5194/acp-13-6993-2013 |
op_doi |
https://doi.org/10.5194/acp-13-6993-2013 |
container_title |
Atmospheric Chemistry and Physics |
container_volume |
13 |
container_issue |
14 |
container_start_page |
6993 |
op_container_end_page |
7005 |
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1766029663411372032 |