12 Jun 2023
 | 12 Jun 2023
Status: this preprint is currently under review for the journal BG.

Environmental controls of non-growing season carbon dioxide fluxes in boreal and tundra environments

Alex Mavrovic, Oliver Sonnentag, Juha Lemmetyinen, Carolina Voigt, Nick Rutter, Paul Mann, Jean-Daniel Sylvain, and Alexandre Roy

Abstract. The carbon cycle in Arctic-boreal regions (ABR) is an important component of the planetary carbon balance, with growing concerns about the consequences of ABR warming on the global climate system. The greatest uncertainty in annual carbon dioxide (CO2) budgets exists during the non-growing season, primarily due to challenges with data availability and limited spatial coverage in measurements. The goal of this study was to determine the main environmental controls of non-growing season CO2 fluxes in ABR over a latitudinal gradient (45° N to 69° N) featuring four different ecosystem types: closed-crown coniferous boreal forest, open-crown coniferous boreal forest, erect-shrub tundra, and prostrate-shrub tundra. CO2 fluxes calculated using a snowpack diffusion gradient method (n = 560) ranged from 0 to 1.05 gC m2 day-1. To assess the dominant environmental controls governing CO2 fluxes, a Random Forest machine learning approach was used. We identified that soil temperature as the main control of non-growing season CO2 fluxes with 68 % of relative model importance, except when soil liquid water occurred during zero degree Celsius curtain conditions (Tsoil ≈ 0 °C and liquid water coexists with ice in soil pores). Under zero-curtain conditions, liquid water content became the main control of CO2 fluxes with 87 % of relative model importance. We observed exponential regressions between CO2 fluxes and soil temperature (RMSE = 0.024 gC m-2 day-1) in frozen soils, as well as liquid water content (RMSE = 0.137 gC m-2 day-1) in zero-curtain conditions. This study is showing the role of several variables on the spatio-temporal variability of CO2 fluxes in ABR during the non-growing season and highlight that the complex vegetation-snow-soil interactions in northern environments must be considered when studying what drives the spatial variability of soil carbon emission during the non-growing season.

Alex Mavrovic et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2023-92', Anonymous Referee #1, 30 Jun 2023
    • AC1: 'Reply on RC1', Alex Mavrovic, 30 Aug 2023
    • AC3: 'Reply on RC1', Alex Mavrovic, 30 Aug 2023
  • RC2: 'Comment on bg-2023-92', Anonymous Referee #2, 11 Aug 2023
    • AC2: 'Reply on RC2', Alex Mavrovic, 30 Aug 2023

Alex Mavrovic et al.

Alex Mavrovic et al.


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Short summary
We present an analysis of soil CO2 emission in boreal and tundra regions during the non-growing season. We show that when the soil is completely frozen, soil temperature is the main control on CO2 emissions. When the soil is around freezing point, with a mix of liquid water and ice, the liquid water content is the main control on CO2 emissions. This study highlight that the vegetation-snow-soil interactions must be considered to understand soil CO2 emission during the non-growing season.