High temporal resolution in-situ measurement of CO₂ fluxes through Arctic shrub-tundra snowpacks

Abstract. Wintertime carbon dioxide (CO₂) emissions from tundra soils likely make a sizable contribution to terrestrial annual Arctic carbon budgets. However, poor availability of wintertime CO₂ flux measurements limits current capacity to quantify the magnitude and variability of non-growing season carbon emissions from Arctic soils, and identify key environmental drivers of CO₂ production and release. To address this, low-cost CO₂ logging systems were developed and deployed in snowpacks at Trail Valley Creek, NT, Canada during late winter periods in 2021–2022 and 2022–2023. CO₂ fluxes calculated from sub-hourly gradients in CO₂ concentrations demonstrated consistent positive (ground-to-atmosphere) emissions, with median flux rates of 0.03 to 0.35 g C m^-2 d^-1, across a range of vegetation types (shrub, tree, tussock) and snow depths (34–136 cm).  Stable carbon isotope (δ¹³C-CO₂) analyses confirmed isotopic enrichment of CO₂ at the base of the snowpack originating from soil emission, and that snowpack gases mixed sequentially with atmospheric CO₂ as they travelled through upper snow layers. Snowpack CO₂ concentration gradients and resultant fluxes were impacted by seasonal increases in air and soil temperatures, especially as near-ground gas temperatures approached the zero-curtain (0 °C) threshold during the winter-spring transition. Positive relationships between CO₂ flux and warming subnivean temperatures across the study site were similar in magnitude to those observed in pan-Arctic winter syntheses. Our results highlight that low-cost sensors may provide a robust and scalable method for monitoring the spatial variability of in-situ winter CO₂ fluxes through snow at high temporal resolution and provide unique insights into winter carbon processes.