The role of snow cover affecting boreal-arctic soil freezeâ•fithaw and carbon dynamics

Northern Hemisphere permafrost affected land ar­ eas contain abont twice as mnch carbon as the global at­ mosphere. This vast carbon pool is vnlnerable to acceler­ ated losses throngh mobilization and decomposition nnder projected global warming. Satellite data records sparming the past 3 decades indicate widespread redactions ( ~ 0.81.3 days decade “ ̂ ) in the mean aimnal snow cover extent and frozen-season dnration across the pan-Arctic domain, coinci­ dent with regional climate warming trends. How the soil car­ bon pool responds to these changes will have a large impact on regional and global climate. Here, we developed a conpled terrestrial carbon and hydrology model framework with a de­ tailed 1-D soil heat transfer representation to investigate the sensitivity of soil organic carbon stocks and soil decompo­ sition to climate warming and changes in snow cover condi­ tions in the pan-Arctic region over the past 3 decades (19822010). Om resnlts indicate widespread soil active layer deep­ ening 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 particnlarly within snrface soil layers (< 0.2 m). The model simnlations also show that seasonal snow cover has a large impact on soil temperatmes, whereby increases in snow cover promote deeper (> 0.5 m) soil layer warm­ ing and soil respiration, while inhibiting soil decomposition from snrface (< 0.2 m) soil layers, especially in colder cli­ mate zones (mean armnal T < -10°C ). Onr resnlts demon­ strate the important control of snow cover on northem 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 per­ mafrost soil carbon dynamics.