LAUSR

Abstract. Winter soil carbon dioxide (CO 2 ) respiration is a significant and understudied component of the global carbon (C) cycle. Winter soil CO 2 fluxes can be surprisingly variable, owing to physical factors such as snowpack properties and wind. This study aimed to quantify the effects of advective transport of CO 2 in soil–snow systems on the subdiurnal to diurnal (hours to days) timescale, use an enhanced diffusion model to replicate the effects of CO 2 concentration depletions from persistent winds, and use a model–measure pairing to effectively explore what is happening in the field. We took continuous measurements of CO 2 concentration gradients and meteorological data at a site in the Cape Breton Highlands of Nova Scotia, Canada, to determine the relationship between wind speeds and CO 2 levels in snowpacks. We adapted a soil CO 2 diffusion model for the soil–snow system and simulated stepwise changes in transport rate over a broad range of plausible synthetic cases. The goal was to mimic the changes we observed in CO 2 snowpack concentration to help elucidate the mechanisms (diffusion, advection) responsible for observed variations. On subdiurnal to diurnal timescales with varying winds and constant snow levels, a strong negative relationship between wind speed and CO 2 concentration within the snowpack was often identified. Modelling clearly demonstrated that diffusion alone was unable to replicate the high-frequency CO 2 fluctuations, but simulations using above-atmospheric snowpack diffusivities (simulating advective transport within the snowpack) reproduced snow CO 2 changes of the observed magnitude and speed. This confirmed that wind-induced ventilation contributed to episodic pulsed emissions from the snow surface and to suppressed snowpack concentrations. This study improves our understanding of winter CO 2 dynamics to aid in continued quantification of the annual global C cycle and demonstrates a preference for continuous wintertime CO 2 flux measurement systems.