Preprints
https://doi.org/10.5194/tc-2020-262
https://doi.org/10.5194/tc-2020-262

  22 Oct 2020

22 Oct 2020

Review status: a revised version of this preprint is currently under review for the journal TC.

Improved ELMv1-ECA Simulations of Zero-Curtain Periods and Cold-season CH4 and CO2 Emissions at Alaskan Arctic Tundra Sites

Jing Tao1,2, Qing Zhu1, William J. Riley1, and Rebecca B. Neumann2 Jing Tao et al.
  • 1Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
  • 2Department of Civil and Environmental Engineering, University of Washington, Seattle, WA, 98195, USA

Abstract. Field measurements have shown that cold-season methane (CH4) and carbon dioxide (CO2) emissions contribute a substantial portion to the annual net carbon emissions in permafrost regions. However, most earth system land models do not accurately reproduce cold-season CH4 and CO2 emissions, especially over the shoulder (i.e., thawing and freezing) seasons. Here we use the Energy Exascale Earth System Model (E3SM) land model version 1 (ELMv1-ECA) to tackle this challenge and fill the knowledge gap of how cold-season CH4 and CO2 emissions contribute to the annual totals at Alaska Arctic tundra sites. Specifically, we improved the ELMv1-ECA soil water phase-change scheme, environmental controls on microbial activity, and cold-season methane transport module. Results demonstrate that both soil temperature and the duration of zero-curtain periods (i.e., the fall period when soil temperatures linger around 0 °C) simulated by the updated ELMv1-ECA were greatly improved, e.g., the Mean Absolute Error in zero-curtain durations at 12 cm depth was reduced by 62 % on average. Furthermore, the simulated cold-season emissions at three tundra sites were improved by 84 % and 81 % on average for CH4 and CO2, respectively. Overall, CH4 and CO2 emitted during the early cold season (Sep. and Oct.), which often includes most of the zero-curtain period in Arctic tundra, accounted for more than 50 % of the total emissions throughout the entire cold season (Sep. to May). From 1950 to 2017, both CO2 emissions during the 12 cm depth zero-curtain period and during the entire cold season showed increasing trends, for example, of 0.26 g C m−2 year−1 and 0.38 g C m−2 year−1 at Atqasuk. This study highlights the importance of zero-curtain periods in facilitating CH4 and CO2 emissions from tundra ecosystems.

Jing Tao et al.

 
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Jing Tao et al.

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Short summary
We improved global land model (ELMv1-ECA) simulations of soil temperature, zero-curtain durations, cold-season CH4 and CO2 net emissions at several Alaskan Arctic tundra sites. We demonstrated that CH4 and CO2 emitted during the zero-curtain period accounted for more than 50 % of the total emissions throughout the entire cold season (Sep. to May). We found that CO2 emissions during soil zero-curtain periods and during the entire cold season both showed increasing trends from 1950 to 2017.