Renconstruction of the past 13C/12C istopic ratio of methane in atmospheric air, induced from firm air analysis
type: Dataset
description: Interstitial air extracted from the firn at 4 polar sites has given access to air samples aging back to a hundred years in sufficient amount for isotopic analysis of CH4, a gas considered to be the second most important responsible for man-induced greenhouse effect. Thus, after optimization of a particularly sensible experimental device (CF-IRMS), 13CH4/12CH4 ratio of air samples pumped in the firn at different depths were measured, whose results lie in remarkable agreement with ratios measured using another experimental method (TDLAS) at the MPI in Mayence (Germany). The recursive use of a physical model of diffusive gas transport in the firn then allowed us to infer, from firn profiles, the likely evolution of atmospheric 13CH4/12CH4 ratio over the last century. This new constraint on CH4 atmospheric budget thus enabled us to confirm the existing assumption of a domining anthropogenic activities responsibility in the 150 % growth of atmospheric methane concentration since pre- industrial times. This constraint has also been applied into a global atmospheric model to test the relevance of a scenario assuming a 20% decrease of the oxidizing capacity of the atmosphere since 1885. Besides, a collaboration with the PSSRI from Open University (United-Kingdom) allowed us to resume development of a method for measurement of CH3D/CH4 ratio in air, and to try to apply it to samples extracted at 2 polar sites and already analyzed in 13C/12C. A sensible method for extraction and analysis of CH4 in air trapped in polar ice has also been developed and successfully tested, which has now to be applied for analysis of pre-industrial air.
issued: 2026-05-17T02:28:24.420742
language: fr
modified: 2026-05-17T02:28:24.420748
contact point: Organization
  fn: CCSD
keyword: atmosphere----pollution
keyword: ch4
keyword: climat----changements
keyword: effet-de-serre
keyword: experimentation
keyword: glace
keyword: infoeu-reposemanticsdoctoralthesis
keyword: isotopie-du-ch4
keyword: neve
keyword: piegeage-des-gaz
keyword: rapport-13ch412ch4
keyword: sdeenvironmental-sciences
keyword: sdustuglsciences-of-the-universe-physicsearth-sciencesglaciology
keyword: signal-atmospherique
keyword: systeme-miranda
keyword: theses
landing page: https://theses.hal.science/tel-00701320

Renconstruction of the past 13C/12C istopic ratio of methane in atmospheric air, induced from firm air analysis
type: Distribution
format: HTML
issued: 2026-05-17T02:28:24.519335
modified: 2026-05-17T02:28:24.360750
access URL: https://theses.hal.science/tel-00701320

test_moissonnage_selune
type: Agent