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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-182
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-182
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 22 Jun 2020

Submitted as: research article | 22 Jun 2020

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This preprint is currently under review for the journal BG.

Investigating the sensitivity of soil respiration to recent snow cover changes in Alaska using a satellite-based permafrost carbon model

Yonghong Yi1,2, John S. Kimball3, Jennifer D. Watts4, Susan M. Natali4, Donatella Zona5,6, Junjie Liu1, Masahito Ueyama7, Hideki Kobayashi8, Walter Oechel5,9, and Charles E. Miller1 Yonghong Yi et al.
  • 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 2Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA, USA
  • 3Numerical Terradynamic Simulation Group, The University of Montana, USA
  • 4Woods Hole Research Center, Falmouth, MA, USA
  • 5Department of Biology, San Diego State University, San Diego, CA, USA
  • 6Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK
  • 7Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
  • 8Institute of Arctic Climate and Environment Research, Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama, Kanagawa 236-0001, Japan
  • 9Department of Geography, College of Life and Environmental Sciences, University of Exeter, Exeter, EX4 4RJ, UK

Abstract. The contribution of soil heterotrophic respiration to the boreal-Arctic carbon (CO2) cycle and its potential feedback to climate change remain poorly quantified. We developed a remote sensing driven permafrost carbon model at intermediate scale (~ 1 km) to investigate how environmental factors affect the magnitude and seasonality of soil heterotrophic respiration in Alaska. The permafrost carbon model simulates snow and soil thermal dynamics, and accounts for vertical soil carbon transport and decomposition at depths up to 3 m below surface. Model outputs include soil temperature profiles and carbon fluxes at 1-km resolution spanning the recent satellite era (2001–2017) across Alaska. Comparisons with eddy covariance tower measurements show that the model captures the seasonality of carbon fluxes, with favorable accuracy in predicting net ecosystem CO2 exchange (NEE) in both tundra (R > 0.8, RMSE = 0.34 g C m−2 d−1) and boreal forest (R > 0.73, RMSE = 0.51 g C m−2 d−1). Benchmark assessments using two regional in-situ datasets indicate that the model captures the complex influence of snow insulation on soil temperature, and the temperature sensitivity of cold-season soil respiration. Across Alaska, we find that seasonal snow cover imposes strong controls on the contribution from different soil depths to total soil carbon emissions. Earlier snow melt in spring promotes deeper soil warming and enhances the contribution of deeper soils to total soil respiration during the later growing season, thereby reducing net ecosystem carbon uptake. Early cold-season soil respiration is closely linked to the number of snow-free days after land surface freezes (R = −0.48, p < 0.1), i.e. the delay in snow onset relative to surface freeze onset. Recent trends toward earlier autumn snow onset in northern Alaska promote a longer zero-curtain period and enhanced cold-season respiration. In contrast, southwestern Alaska shows a strong reduction in the number of snow-free days after land surface freeze onset, leading to earlier soil freezing and a large reduction in cold-season soil respiration. Our results also show non-negligible influences of sub-grid variability of surface conditions on the model simulated CO2 seasonal cycle, especially during the early cold season at 10-km scale. Our results demonstrate the critical role of snow cover affecting the seasonality of soil temperature and respiration and highlight the challenges of incorporating these complex processes into future projections of boreal-Arctic carbon cycle.

Yonghong Yi et al.

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Short summary
We developed a remote sensing driven permafrost carbon model at 1-km to evaluate soil respiration sensitivity to recent snow cover changes across Alaska. Results indicate earlier snow melt enhances soil respiration throughout the growing season and reduces annual carbon uptake, while early cold-season soil respiration is closely linked to the number of snow-free days after surface freezes. These results confirm the critical control of snow cover on annual and seasonal boreal-Arctic carbon cycle.
We developed a remote sensing driven permafrost carbon model at 1-km to evaluate soil...
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