Source: AGU Advances
High northern latitudes store vast amounts of carbon in frozen soils, and their vulnerability to loss with warming has been the subject of intense debate for decades. Warming temperatures lead to changes with opposite effects. Longer growing seasons lead to increased productivity and shifts to shrub vegetation that can store more carbon. Warmer temperatures also increase respiration and carbon loss, and geomorphic changes with melting permafrost can lead to local, intense losses of carbon.
Pedron et al.  identify a new contributor to change. They analyzed records of snow cover, finding that while the Arctic snow-covered season was becoming shorter, mid-winter snowpack often increased. They observed a phenomenon identified in alpine tundra by Russ Monson’s group in Colorado, that increased snow, and even colder winters can increase wintertime soil biological activity by better insulating the soil and allowing more decomposition during the long winters.
The authors used a long-running snow manipulation experiment at the Toolik Biological Station in Alaska, initiated in 1994, the team resampled it in 2021. The length of the experiment allows slow processes to unfold, overcoming the variability inherent in year-to-year snowpack dynamics. The results showed dominant effects of snowpack on soil properties-as the authors say, “Northern ecosystems are shaped by snow”. They show that snowpack changes consistent with observed climate trends, caused changes to carbon sources and mobilized ancient carbon, determined with 14C measurements. The losses of carbon accelerated nutrient release, favoring shrub encroachment and increasing productivity, while reducing carbon inputs deeper in the soil.
As a consequence, legacy carbon, ancient carbon was respired all year long with increased snowpack. The studies not only increase concern about the long-term stability of northern carbon but also reveal the complex and not-always-intuitive interactions that determine the net carbon balance. Long-term experiments play a crucial role in climate science’s toolkit, and this paper demonstrates their unique value and the importance of sustained effort.
Citation: Pedron, S. A., Jespersen, R. G., Xu, X., Khazindar, Y., Welker, J. M., & Czimczik, C. I. (2023). More snow accelerates legacy carbon emissions from Arctic permafrost. AGU Advances, 4, e2023AV000942. https://doi.org/10.1029/2023AV000942
—Dave Schimel, Editor, AGU Advances