Modeling CH4 emissions from Arctic tundra: Processes behind emissions pulses and the potential for a negative feedback
Abstract
Existing climate change models contain poorly-constrained influences from thawing Arctic permafrost and subsequent greenhouse gas emissions, particularly the release of CH4, despite the fact that Arctic permafrost contains approximately one half of the total below-ground organic carbon on our planet. One of the most widely cited models for CH4 emissions from permafrost, the methane dynamics module (MDM) by Zhuang et al. (2004), has never been explicitly examined for effectiveness at non-Alaskan sites. In order to investigate the processes controlling CH4 emissions from Arctic tundra and the effectiveness of the model, simulations were carried out for Axel Heiberg Island, Canada; Zackenberg, Greenland; and Happy Valley, Alaska. Results from the simulations show that CH4 emissions occur primarily through quick emissions pulses that occur at the onset of surface soil freezing and thawing. Previous studies have proposed that these pulses are due to the inhibition of diffusion by surface ice. Alternatively, it has also been proposed that emissions pulses are due to frost action, with expansion and contraction of the soil column squeezing out CH4 trapped between soil particles. Simulations here support the first hypothesis, and show that emissions pulses at the onset of freezing and thawing are both due to the inhibition of CH4 diffusion by surface soil that is saturated or frozen. Investigations into the effectiveness of the MDM suggest that the maximum methanogenesis and methanotrophy rates are severely under-constrained and that the current structure of the MDM may be unable to accurately project future CH4 emissions. Eliminating some of the modifiers and using new data to redefine maximum rates as more constrained can improve the ability of the MDM to predict current CH4 emissions from Axel Heiberg. This process could also be carried out for other sites and should greatly improve the ability of the MDM to simulate current and future CH4 emissions. Preliminary results suggest a potential negative feedback between Arctic tundra CH4 emissions and the climate system, where warmer summers increase CH4 consumption by causing an earlier summer thaw and later onset of freezing. This would lead to smaller CH4 emissions pulses, as CH4 would have less time to build up in the soil column, and longer periods of CH4 consumption during the summer, as methanotrophs can oxidize CH4 faster than methanogens can produce it, causing CH4 to diffuse into the soil from the atmosphere.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.B21D0405M
- Keywords:
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- 0466 BIOGEOSCIENCES / Modeling;
- 0475 BIOGEOSCIENCES / Permafrost;
- cryosphere;
- and high-latitude processes;
- 0793 CRYOSPHERE / Biogeochemistry;
- 0798 CRYOSPHERE / Modeling