Journal cover Journal topic
Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
doi:10.5194/gmd-2017-23
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Model description paper
20 Feb 2017
Review status
This discussion paper is under review for the journal Geoscientific Model Development (GMD).
Implementation of methane cycling for deep time, global warming simulations with the DCESS Earth System Model (Version 1.2)
Gary Shaffer1,2, Esteban Fernández Villanueva3, Roberto Rondanelli3,4, Jens Olaf Pepke Pedersen5, Steffen Malskær Olsen6, and Matthew Huber7,8 1GAIA-Antarctica, Universidad de Magallanes, Punta Arenas, Chile
2Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen Ø, Denmark
3Department of Geophysics, University of Chile, Santiago, Chile
4Center for Climate and Resilience Research, University of Chile, Santiago, Chile
5National Space Institute, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
6Danish Meteorological Institute, 2100 Copenhagen Ø, Denmark
7Earth, Atmospheric and Planetary Sciences, Purdue University, West Lafayette, IN 47907, USA
8Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 03814, USA
Abstract. Geological records reveal a number of ancient, large and rapid negative excursions of carbon-13 isotope. Such excursions can only be explained by massive injections of depleted carbon to the Earth System over a short duration. These injections may have forced strong global warming events, sometimes accompanied by mass extinctions, for example the Triassic-Jurassic and End-Permian extinctions, 201 and 252 million years ago. In many cases evidence points to methane as the dominant form of injected carbon, whether as thermogenic methane, formed by magma intrusions through overlying carbon-rich sediment, or from warming-induced dissociation of methane hydrate, a solid compound of methane and water found in ocean sediments. As a consequence of the ubiquity and importance of methane in major Earth events, Earth System models should include a comprehensive treatment of methane cycling but such a treatment has often been lacking. Here we implement methane cycling in the Danish Center for Earth System Science (DCESS) model, a simplified but well-tested Earth System Model of Intermediate Complexity. We use a generic methane input function that allows variation of input type, size, time scale and ocean-atmosphere partition. To be able to treat such massive inputs more correctly, we extend the model to deal with ocean suboxic/anoxic conditions and with radiative forcing and methane lifetimes appropriate for high atmospheric methane concentrations. With this new model version, we carried out an extensive set of simulations for methane inputs of various sizes, time scales and ocean-atmosphere partitions to probe model behaviour. We find that larger methane inputs over shorter time scales with more methane dissolving in the ocean lead to ever-increasing ocean anoxia with consequences for ocean life and global carbon cycling. Greater methane input directly to the atmosphere leads to more warming and, for example, greater carbon dioxide release from land soils. Analysis of synthetic sediment cores from the simulations provides guidelines for the interpretation of real sediment cores spanning the warming events. With this improved DCESS model version and paleo-reconstructions, we are now better armed to gauge the amounts, types, time scales and locations of methane injections driving specific, observed deep time, global warming events.

Citation: Shaffer, G., Fernández Villanueva, E., Rondanelli, R., Pedersen, J. O. P., Olsen, S. M., and Huber, M.: Implementation of methane cycling for deep time, global warming simulations with the DCESS Earth System Model (Version 1.2), Geosci. Model Dev. Discuss., doi:10.5194/gmd-2017-23, in review, 2017.
Gary Shaffer et al.
Gary Shaffer et al.
Gary Shaffer et al.

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Short summary
We include methane cycling in the simplified but well-tested Danish Center for Earth System Science model. We now can deal with very large methane inputs to the Earth System that can lead to much methane in the atmosphere, extreme warming and ocean dead zones. We now can study ancient global warming events, probably forced by methane inputs. Some such events were accompanied by mass extinctions. We wish to understand such events, both for learning about the past and for looking into the future.
We include methane cycling in the simplified but well-tested Danish Center for Earth System...
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