Reconstruction of the carbon isotopic composition of methane over the last 50 yr based on firn air measurements at 11 polar sites

• Main Authors: Sapart, C.J., Martinerie, Patricia, Chappellaz, Jérôme, van de Wal, R.S.W., Sperlich, P., van Der Veen, C., Bernard, Serge, Sturges, W. T., Blunier, T., Witrant, Emmanuel, Schwander, Jakob, Etheridge, D., Röckmann, T.
• Other Authors: Institute for Marine and Atmospheric Research Utrecht (IMAU), Universiteit Utrecht / Utrecht University Utrecht, Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Centre for Ice and Climate Copenhagen, Niels Bohr Institute Copenhagen (NBI), Faculty of Science Copenhagen, University of Copenhagen = Københavns Universitet (UCPH)-University of Copenhagen = Københavns Universitet (UCPH)-Faculty of Science Copenhagen, University of Copenhagen = Københavns Universitet (UCPH)-University of Copenhagen = Københavns Universitet (UCPH), Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France, School of Environmental Sciences Norwich, University of East Anglia Norwich (UEA), GIPSA - Infinite Dimensional Dynamics (GIPSA-INFINITY), GIPSA Pôle Automatique et Diagnostic (GIPSA-PAD), Grenoble Images Parole Signal Automatique (GIPSA-lab), Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA)-Grenoble Images Parole Signal Automatique (GIPSA-lab), Climate and Environmental Physics Bern (CEP), Physikalisches Institut Bern, Universität Bern / University of Bern (UNIBE)-Universität Bern / University of Bern (UNIBE), Centre for Australian Weather and Climate Research (CAWCR)
• Format: Report
• Language: English
• Published: HAL CCSD 2022
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology; Greenland; Grav; Antarc*; Antarctica; ice core
• Online Access: https://hal.science/hal-00821201; https://hal.science/hal-00821201/document; https://hal.science/hal-00821201/file/acpd-12-9587-2012.pdf; https://doi.org/10.5194/acpd-12-9587-2012

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 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. We present an attempt to reconcile methane carbon isotope records from 11 firn sites from both Greenland and Antarctica to reconstruct a consistent 13C(CH4) history over the last 50 yr. In the firn, the atmospheric signal is altered mainly by diffusion and grav itation. These processes are taken into account by firn transport models. We show that isotope reconstructions from individual sites are not always mutually consistent among the different sites. Therefore we apply for the first time a multisite isotope inversion to reconstruct an atmospheric isotope history that is constrained by all individual sites, generating a multisite “best-estimate” scenario. This scenario is compared to ice core data, atmospheric air archive results and direct atmospheric monitoring data.