Preprints
https://doi.org/10.5194/cp-2020-131
https://doi.org/10.5194/cp-2020-131

  19 Oct 2020

19 Oct 2020

Review status: this preprint is currently under review for the journal CP.

CH4 and N2O fluctuations during the penultimate deglaciation

Loïc Schmidely1, Christoph Nehrbass-Ahles2, Jochen Schmitt1, Juhyeong Han1, Lucas Silva1, Jinwha Shin3,a, Fortunat Joos1, Jérôme Chappellaz3, Hubertus Fischer1, and Thomas F. Stocker1 Loïc Schmidely et al.
  • 1Climate and Environmental Physics, Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, Bern 3012, Switzerland
  • 2Department of Earth Sciences, University of Cambridge, Cambridge, UK
  • 3CNRS, Univ. Grenoble-Alpes, Institut des Géosciences de l’Environnement (IGE), Grenoble, France
  • apresent address: Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, T6G 2E3, Canada

Abstract. Deglaciations are characterized by the largest natural changes in methane (CH4) and nitrous oxide (N2O) concentrations of the past 800 thousand years. Reconstructions of millennial to centennial-scale variability within these periods are mostly restricted to the last deglaciation. In this study, we present composite records of CH4 and N2O concentrations from the EPICA Dome C ice core covering the penultimate deglaciation at temporal resolutions of about ~ 100 years. Our data permit the identification of centennial-scale fluctuations standing out of the overall transition to interglacial levels. These features occurred in concert with reinvigorations of the Atlantic Meridional Overturning Circulation (AMOC) and northward shifts of the Intertropical Convergence Zone. The abrupt CH4 and N2O rises at about ~ 134 and ~ 128 thousand of years before present (hereafter ka BP) are assimilated to the fluctuations accompanying the Dansgaard–Oeschger events of the last glacial period, while rising N2O levels at ~ 130.5 ka BP are assimilated to a pattern of increasing N2O concentrations that characterized the end of Heinrich stadials. We suggest the 130.5-ka event to be driven by a partial reinvigoration of the AMOC. Overall, the CH4 and N2O fluctuations during the penultimate deglaciation exhibit modes of variability that are also found during the last deglaciation. However, trace gas responses may differ for similar type of climatic events, as exemplified by the reduced amplitude and duration of the 134-ka event compared to the fluctuations of the Bølling–Allerød during the last deglaciation.

Loïc Schmidely et al.

 
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Loïc Schmidely et al.

Loïc Schmidely et al.

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Short summary
Using ancient gas trapped in polar glaciers, we reconstructed the atmospheric concentrations of methane and nitrous oxide over the penultimate deglaciation to study their response to major climate changes. We show this deglaciation to be characterized by fluctuations in concentration correlated to varying strength of the meridional circulation in the Atlantic Ocean, which is believed to have modulated methane and nitrous oxide emissions during the penultimate deglaciation.