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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/gmd-2020-32
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gmd-2020-32
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: development and technical paper 09 Mar 2020

Submitted as: development and technical paper | 09 Mar 2020

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This preprint is currently under review for the journal GMD.

Oceanic and atmospheric methane cycling in the cGENIE Earth system model

Christopher T. Reinhard1,2,3, Stephanie Olson2,4,5, Sandra Kirtland Turner6, Cecily Pälike7, Yoshiki Kanzaki6, and Andy Ridgwell6 Christopher T. Reinhard et al.
  • 1School of Earth and Atmospheric Sciences, GeorgiaInstitute of Technology, Atlanta, GA 30332, USA
  • 2NASA Astrobiology Institute, Alternative Earths Team, Riverside, CA, USA
  • 3NASA Nexus for Exoplanet System Science (NExSS)Upside-Down Biospheres Team, Georgia Institute of Technology, Atlanta, GA, USA
  • 4Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA
  • 5Department of Earth, Atmospheric, and Planetary Science, Purdue University, West Lafayette, IN 47907, USA
  • 6Department of Earth Sciences, University of California, Riverside, Riverside, CA 92521, USA
  • 7MARUM Center for Marine Environmental Sciences, University of Bremen, Germany

Abstract. The methane (CH4) cycle is a key component of the Earth system that links planetary climate, biological metabolism, and the global biogeochemical cycles of carbon, oxygen, sulfur, and hydrogen. However, currently lacking is a numerical model capable of simulating a diversity of environments in the ocean where CH4 can be produced and destroyed, and with the flexibility to be able to explore not only relatively recent perturbations to Earth’s CH4 cycle but also to probe CH4 cycling and associated climate impacts under the very low-O2 conditions characteristic of most of Earth history and likely widespread on other Earth-like planets. Here, we present a refinement and expansion of the ocean-atmosphere CH4 cycle in the intermediate-complexity Earth system model cGENIE, including parameterized atmospheric O2-O3-CH4 photochemistry and schemes for microbial methanogenesis, aerobic methanotrophy, and anaerobic oxidation of methane (AOM). We describe the model framework, compare model parameterizations against modern observations, and illustrate the flexibility of the model through a series of example simulations. Though we make no attempt to rigorously tune default model parameters, we find that simulated atmospheric CH4 levels and marine dissolved CH4 distributions are generally in good agreement with empirical constraints for the modern and recent Earth. Finally, we illustrate the model’s utility in understanding the time-dependent behavior of the CH4 cycle resulting from transient carbon injection into the atmosphere, and present model ensembles that examine the effects of atmospheric pO2, oceanic dissolved SO42− and the thermodynamics of microbial metabolism on steady-state atmospheric CH4 abundance. Future model developments will address the sources and sinks of CH4 associated with the terrestrial biosphere and marine CH4 gas hydrates, both of which will be essential for comprehensive treatment of Earth’s CH4 cycle during geologically recent time periods.

Christopher T. Reinhard et al.

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Christopher T. Reinhard et al.

Data sets

Reinhard.GMD.RateData C. Reinhard, S. Olson, S. Kirtland Turner, C. Pälike, Y. Kanzaki, and A. Ridgwell https://doi.org/10.5281/zenodo.3699537

Model code and software

cgenie.muffin v0.9.10 C. Reinhard and A. Ridgwell https://doi.org/10.5281/zenodo.3620846

Christopher T. Reinhard et al.

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Latest update: 28 Mar 2020
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Short summary
We provide documentation and testing of new developments to the oceanic and atmospheric methane cycles in the cGENIE Earth system model. The model is designed to explore Earth's methane cycle across a wide range of timescales and scenarios, but in particular assessing mean climate state and climate perturbations in Earth's deep past. We further document the impact of atmospheric oxygen levels and ocean chemistry on fluxes of methane to the atmosphere from the ocean biosphere.
We provide documentation and testing of new developments to the oceanic and atmospheric methane...
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