09 May 2023
 | 09 May 2023
Status: this preprint is open for discussion.

Simulating net ecosystem exchange under seasonal snow cover at an Arctic tundra site

Victoria R. Dutch, Nick Rutter, Leanne Wake, Oliver Sonnentag, Gabriel Hould Gosselin, Melody Sandells, Chris Derksen, Branden Walker, Gesa Meyer, Richard Essery, Richard Kelly, Phillip Marsh, Julia Boike, and Matteo Detto

Abstract. Estimates of winter (snow-covered non-growing season) CO2 fluxes across the Arctic region vary by a factor of three and a half, with considerable variation between measured and simulated fluxes. Measurements of snow properties, soil temperatures and net ecosystem exchange (NEE) at Trail Valley Creek, NWT, Canada, allowed evaluation of simulated winter NEE in a tundra environment with the Community Land Model (CLM5.0). Default CLM5.0 parameterisations did not adequately simulate winter NEE in this tundra environment, with near-zero NEE (< 0.01 g C m−2 d−1) simulated between November and mid-May. In contrast, measured NEE was broadly positive (indicating net CO2 release) from snow cover onset until late April. Changes to the parameterisation of snow thermal conductivity, required to correct for a cold soil temperature bias, reduced the duration for which no NEE was simulated. Parameter sensitivity analysis revealed the critical role of the minimum soil moisture threshold on decomposition (Ψmin) in regulating winter soil respiration. The default value of this parameter (Ψmin) was too high, preventing simulation of soil respiration for the vast majority of the snow-covered season. In addition, the default rate of change of soil respiration with temperature (Q10) was too low, further contributing to poor model performance during winter. As Ψmin and Q10 had opposing effects on the magnitude of simulated winter soil respiration, larger negative values of Ψmin and larger positive values of Q10 are required to simulate wintertime NEE more adequately.

Victoria R. Dutch et al.

Status: open (until 20 Jun 2023)

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Victoria R. Dutch et al.

Victoria R. Dutch et al.


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Short summary
We undertake a sensitivity study of three different parameters on the simulation of net ecosystem exchange during the snow-covered non-growing season at an Arctic tundra site. Simulations are compared to eddy covariance measurements, with near-zero NEE simulated despite observed CO2 release. We then consider how to parameterise the model better in Arctic tundra environments on both sub-seasonal timescales and cumulatively throughout the snow-covered non-growing season.