| 25 Nov 2025
Fine-scale spatial variability of winter CO2 and CH4 fluxes in Arctic tundra derived from snowpack gradient measurements
Abstract. Winter carbon dioxide (CO2) and methane (CH4) fluxes from soils under seasonal snowpacks make non-negligible, yet poorly constrained contributions to annual carbon budgets across Arctic regions. Quantifying these fluxes and their spatial variance will better constrain uncertainties in simulations of winter carbon fluxes from terrestrial biosphere models. We address this gap by measuring and identifying patterns and spatial variability in CO2 and CH4 soil-atmosphere fluxes through late winter snowpacks at an upland tundra site in the western Canadian Arctic. Instantaneous fluxes were calculated from CO2 and CH4 microsite concentration gradients at 10 cm to 20 cm vertical resolution (n = 119) through the snowpack across five homogeneous surface covers, representing dominant vegetation types. We measured consistent soil-to-atmosphere CO2 fluxes but with significantly different rates across surface covers (0.8 to 100 mgC m-2 day-1), which were strongly influenced by snow depth and soil surface temperature, exhibiting higher emissions under deeper snowpacks and warmer soil surfaces. CH4 fluxes were also coupled to soil surface temperature and varied between −0.04 and 0.08 mgC m-2 day-1. Persistent CH4 uptake was observed in warmer soils (-6.0 to -0.5 °C) in a sparsely populated black spruce and shrub dominated area with deep snow, indicating active methane oxidation during winter. Microsite scale CO2 and CH4 fluxes were statistically independent of vertical snow microstructure, indicating that winter fluxes could be reliably calculated from single gas concentration at the soil-snow interface, negating the need for additional snowpack gas measurements. These results open new avenues for quantifying fine-scale spatial variability of wintertime CO2 and CH4 fluxes in Arctic tundra, which can constrain biogeochemical process representations in terrestrial biosphere models and inform spatial upscaling methodologies.
Gabriel , great job on this and thanks so much for continuing to focus on winter emissions so so important.
However, you have missed my program's beginning of this modern day (past ~ 3 decades) field of research which was initially criticized when I presented our initial NSF funded data from Arctic Alaska in CPH at the 1997 ITEX meeting. I showed the flux data, measurable and argued that when winter emissions (~240 days of snow cover in N AK) were added to summer net fluxes, the tundra was a net C source: "Jeff you are crazy". how can all that SOM, permafrost be present if the system is a net C source ?came the audience challenges
my reply was today is different than the past and we now have real emission data from what makes the Arctic, the Arctic, winter.
I have been delighted see Webb, Natalie, and others, including your team, join my winter emission crusade.
These are some of the absolute foundational papers that you should be including in your introduction of the "issue" and in the discussion as to how this data compares
to what the Welker program discovered decades ago and continue today.
Thank you for all that you and your team are doing but knowing and recognizing the origins of this research theme, is essential to educating the readers on the foudational science and
how your new science continues to strengthen our understanding of 2/3 of the Arctic's calendar :)
The first 4 are in many ways the "beginning of the modern winter C emission studies initiated by my team/s", W Ochel's group also published a 1997 paper as well.
And, our continued contributions with packages like Natali et al. 2019
Fahnestock, J. T., Jones, M. H., Brooks, P. D., Walker, D. A., & Welker, J. M. (1998) Winter and early spring CO₂ flux from tundra communities of northern Alaska. Journal of Geophysical Research 102(D22):29925-29931.
Fahnestock, J. T., Jones, M. H., Brooks, P. D., & Welker, J. M. (1999) Significant CO₂ emissions from tundra soils during winter: Implications for annual carbon budgets of arctic communities. Global Biogeochemical Cycles 13:775-779.
Jones, M. H., Fahnestock, J. T., & Welker, J. M. (1999) Early and late winter CO₂ efflux from Arctic tundra in the Kuparuk River watershed, Alaska. Arctic, Antarctic and Alpine Research 31:187-190.
Welker, J. M., Fahnestock, J. T., & Jones, M. H. (2000) Annual CO₂ flux from dry and moist arctic tundra: Field responses to increases in summer temperature and winter snow depth. Climatic Change 44:139-150.
Schimel, J., Fahnestock, J., Michaelson, G., Mikan, C., Ping, C., Romanovsky, V., & Welker, J. M. (2006) Cold-season production of CO₂ in Arctic soils: Can laboratory and field estimates be reconciled through a simple modeling approach? Arctic, Antarctic and Alpine Research 38(2):249-255.
Sullivan, P. F., Welker, J. M., Arens, S. J. T., & Sveinbjörnsson, B. (2008) Continuous estimates of CO₂ efflux from arctic and boreal soils during the snow-covered season in Alaska. JGR Biogeosciences 113:G04009.
Nowinski, N., Taneva, L., Trumbore, S., & Welker, J. M. (2010) Decomposition of old organic matter as a result of deeper active layers in a snow depth manipulation experiment. Oecologia 163(3):785-792.
Lupascu, M., Welker, J. M., Xu, X., & Czimczik, C. I. (2014) Rates and radiocarbon content of summer ecosystem respiration in response to long-term deeper snow in the High Arctic of NW Greenland. JGR Biogeosciences. doi.org/10.1002/2013JG002494
Lupascu, M., Czimczik, C. I., Welker, M., Cooper, L., & Welker, J. M. (2018) Winter ecosystem respiration and sources of CO₂ from the High Arctic tundra of Svalbard: Response to a deeper snow experiment. JGR Biogeosciences. doi.org/10.1029/2018JG004396.
Ala-aho, P., Welker, J. M., Bailey, H., Pedersen, S., Kopec, B., Klein, E., Mellat, M., Mustonen, K., Noor, K., & Marttila, H. (2021) Arctic snow isotope hydrology: A comparative snow-water vapor study. Atmosphere. doi.org/10.3390/atmos12020150
Rixen, C., Hoye, T., Welker, J. M., et al. (2022) Winters are changing: snow effects on Arctic and alpine tundra ecosystems. Arctic Science. doi.org/10.1139/as-2020-0041
Pedron, S., Jespersen, R. G., Xu, X., Khazindar, Y., Welker, J. M., & Czimczik, C. (2023) More snow accelerates legacy carbon emissions from Arctic permafrost. AGU Advances. doi.org/10.1029/2023AV000942
Kantola, N., Welker, J. M., Leffler, A. J., et al. (2025) Impacts of winter climate change on northern forest understory carbon dioxide exchange determined by reindeer grazing. Science of the Total Environment. doi.org/10.1016/j.scitotenv.2025.180089.