Articles | Volume 12, issue 19
Research article
13 Oct 2015
Research article |  | 13 Oct 2015

The role of snow cover affecting boreal-arctic soil freeze–thaw and carbon dynamics

Y. Yi, J. S. Kimball, M. A. Rawlins, M. Moghaddam, and E. S. Euskirchen

Abstract. Northern Hemisphere permafrost affected land areas contain about twice as much carbon as the global atmosphere. This vast carbon pool is vulnerable to accelerated losses through mobilization and decomposition under projected global warming. Satellite data records spanning the past 3 decades indicate widespread reductions (~ 0.8–1.3 days decade−1) in the mean annual snow cover extent and frozen-season duration across the pan-Arctic domain, coincident with regional climate warming trends. How the soil carbon pool responds to these changes will have a large impact on regional and global climate. Here, we developed a coupled terrestrial carbon and hydrology model framework with a detailed 1-D soil heat transfer representation to investigate the sensitivity of soil organic carbon stocks and soil decomposition to climate warming and changes in snow cover conditions in the pan-Arctic region over the past 3 decades (1982–2010). Our results indicate widespread soil active layer deepening across the pan-Arctic, with a mean decadal trend of 6.6 ± 12.0 (SD) cm, corresponding to widespread warming. Warming promotes vegetation growth and soil heterotrophic respiration particularly within surface soil layers (≤ 0.2 m). The model simulations also show that seasonal snow cover has a large impact on soil temperatures, whereby increases in snow cover promote deeper (≥ 0.5 m) soil layer warming and soil respiration, while inhibiting soil decomposition from surface (≤ 0.2 m) soil layers, especially in colder climate zones (mean annual T ≤ −10 °C). Our results demonstrate the important control of snow cover on northern soil freeze–thaw and soil carbon decomposition processes and the necessity of considering both warming and a change in precipitation and snow cover regimes in characterizing permafrost soil carbon dynamics.

Short summary
We found that regional warming promotes widespread deepening of soil thaw in the pan-Arctic area; continued warming will most likely promote permafrost degradation in the warm permafrost areas. We also found that deeper snowpack enhances soil respiration from deeper soil carbon pool more than temperature does, particularly in the cold permafrost areas, where a large amount of soil carbon is stored in deep perennial frozen soils but is potentially vulnerable to mobilization from climate change.
Final-revised paper