Abstract
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.
Highlights
The northern high latitudes contain about twice as much carbon as the global atmosphere, largely stored in permafrost and seasonally thawed soil active layers (Hugelius et al, 2014)
The model simulations were generally consistent with observed daily carbon fluxes from the 20 eddy covariance (EC) tower sites across the pan-Arctic domain (Table 2), with mean R values of 0.84 ± 0.11 (SD) for gross primary productivity (GPP) and 0.63 ± 0.17 for net ecosystem exchange (NEE), and mean RMSE differences of 1.44 ± 0.50 g C m−2 d−1 for GPP and 1.04 ± 0.36 g C m−2 d−1 for NEE
We developed a coupled hydrology and terrestrial carbon flux modeling framework to evaluate the sensitivity of soil thermal and carbon dynamics to snow cover and recent climate variations across the pan-Arctic basin and Alaska during the past 3 decades (1982–2010)
Summary
The northern high latitudes contain about twice as much carbon as the global atmosphere, largely stored in permafrost and seasonally thawed soil active layers (Hugelius et al, 2014). This vast carbon pool is vulnerable to accelerated losses through mobilization and decomposition under regional warming, with potentially large global carbon and climate impacts (Koven et al, 2011; Schaefer et al, 2011; Schuur et al, 2015). Widespread soil thawing and permafrost degradation in the boreal and Arctic have been reported
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