Environmental controls of winter soil carbon dioxide fluxes in boreal and tundra environments

• Published in: Biogeosciences
• Main Authors: Mavrovic, Alex, Sonnentag, Oliver, Lemmetyinen, Juha, Voigt, Carolina, Rutter, Nick, Mann, Paul, Sylvain, Jean-Daniel, Roy, Alexandre
• Format: Text
• Language: English
• Published: 2023
• Subjects: Tundra
• Online Access: https://doi.org/10.5194/bg-20-5087-2023; https://bg.copernicus.org/articles/20/5087/2023/

The carbon cycle in Arctic–boreal regions (ABRs) is an important component of the planetary carbon balance, with growing concerns about the consequences of ABR warming for the global climate system. The greatest uncertainty in annual carbon dioxide ( CO 2 ) budgets exists during winter, 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 winter CO 2 fluxes in ABRs over a latitudinal gradient (45 ∘ 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. CO 2 fluxes calculated using a snowpack diffusion gradient method ( n =560 ) ranged from 0 to 1.05 g C m 2 d −1 . To assess the dominant environmental controls governing CO 2 fluxes, a random forest machine learning approach was used. We identified soil temperature as the main control of winter CO 2 fluxes with 68 % of relative model importance, except when soil liquid water occurred during 0 ∘ C curtain conditions (i.e., T soil ≈0 ∘ C and liquid water coexist with ice in soil pores). Under zero-curtain conditions, liquid water content became the main control of CO 2 fluxes with 87 % of relative model importance. We observed exponential regressions between CO 2 fluxes and soil temperature in fully frozen soils ( RMSE=0.024 g C m - 2 d - 1 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="56pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="846265b129470ed2a785e3fc2495bc89"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-5087-2023-ie00001.svg" width="56pt" height="15pt" src="bg-20-5087-2023-ie00001.png"/> </svg:svg> 70.3 % of mean F CO 2 <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="e6fbe75052c27002d7e521aeffa5e738"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" ...