Explaining CO<sub>2</sub> fluctuations observed in snowpacks

Abstract

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.

Soil respiration and controls in warmer winter: A snow manipulation study in postfire and undisturbed black pine forests

“…Some authors explained that the CO 2 emissions continue during the winter period despite a freezing temperature because of the ability of soil organisms to adjust and adapt their metabolic processes even at −7°C soil temperatures (Brooks et al, 1996;Coxson & Parkinson, 1987;Flanagan & Bunnell, 1980;Graham et al, 2018).…”

Exploring the potential of forest snow modelling at the tree and snowpack layer scale

“…Snowpack properties such as surface density and presence of ice layers are key features impacting wildlife ecology, affecting animal movement, pray-predator interactions, winter habitats, and foraging success (Sullender et al, 2023;Cosgrove et al, 2021). Gas transfer through the snowpack is also impacted by microstructural properties, with implications for wintertime greenhouse gas exchange in boreal environments (Pirk et al, 2016;Graham and Risk, 2018). Finally, knowledge of snow microstructure and/or layer-scale properties is key for the interpretation of certain remote sensing retrievals, e.g.…”

Predicting Peatland Net Ecosystem Exchange of CO2 during the Non-Growing Season using Machine Learning

“…With a greater proportion of NGS precipitation falling as rain [93][94][95] , rain-on-snow events can result in wetter soils and reduced or removed snow coverage. Under these conditions, photosynthetic activity during the NGS may play an increasingly important role in the annual C budget of the Mer Bleue Bog and, by extension, other temperate and boreal peatlands 96,97 .…”

“…A positive relationship is expected as turbulent exchanges of CO2, heat and moisture are driven by forced convection during the NGS when the surface is snow covered and the atmosphere remains neutral or stable. In addition, wind-induced ventilation of the snowpack can cause pulse emissions of CO2 stored in the snow and the porous and unsaturated near-surface peat 96,97 . Turbulent exchanges of heat and moisture play important roles in governing the snowpack energy balance 98,99 .Wind can therefore be indirectly linked to subsurface CO2 production processes through its effects on energy fluxes into the ground.…”