Ecosystem and soil respiration radiocarbon detects old carbon release as a fingerprint of warming and permafrost destabilization with climate change

Abstract

The permafrost region has accumulated organic carbon in cold and waterlogged soils over thousands of years and now contains three times as much carbon as the atmosphere. Global warming is degrading permafrost with the potential to accelerate climate change as increased microbial decomposition releases soil carbon as greenhouse gases. A 19-year time series of soil and ecosystem respiration radiocarbon from Alaska provides long-term insight into changing permafrost soil carbon dynamics in a warmer world. Nine per cent of ecosystem respiration and 23% of soil respiration observations had radiocarbon values more than 50‰ lower than the atmospheric value. Furthermore, the overall trend of ecosystem and soil respiration radiocarbon values through time decreased more than atmospheric radiocarbon values did, indicating that old carbon degradation was enhanced. Boosted regression tree analyses showed that temperature and moisture environmental variables had the largest relative influence on lower radiocarbon values. This suggested that old carbon degradation was controlled by warming/permafrost thaw and soil drying together, as waterlogged soil conditions could protect soil carbon from microbial decomposition even when thawed. Overall, changing conditions increasingly favoured the release of old carbon, which is a definitive fingerprint of an accelerating feedback to climate change as a consequence of warming and permafrost destabilization. This article is part of the Theo Murphy meeting issue ‘Radiocarbon in the Anthropocene’.

Exploring the interplay between soil thermal and hydrological changes and their impact on carbon fluxes in permafrost ecosystems

“…While the direct effect of rising air temperatures has been linked to an increase in vegetation productivity in warming experiments across northern ecosystems [93,94], the increased risks of extreme warming events, droughts, disturbances, and heightened competition among plant communities that have been associated with warming can also result in reduced vegetation productivity [95,96]. The correlation analysis showed that GPP and air temperature have a significant negative correlation at IMN (table S4).…”

A special issue preface: Radiocarbon in the Anthropocene

“…However, increased asymmetry in transit time distributions reflects the differing carbon dynamics of low- versus high-latitude ecosystems, with decreasing transit times in the former and increasing transit times in the latter due to the respiration of long-stored carbon. In an observational study that relates to the findings of Sierra et al , Schuur et al [ 4 ] describe results from almost 20 years of time-series CO 2 flux and radiocarbon measurements at a permafrost site in Alaska where carbon has been stored in frozen and waterlogged soils that shed light on long-term ecosystem and carbon cycle perturbations in a region of the world that is experiencing the accelerated climate change. The detection of respired CO 2 with depleted 14 C values relative to atmospheric CO 2 provides evidence of old permafrost soil C degradation, and a steeper trajectory in respired 14 CO 2 decrease relative to the atmosphere over the time series indicates that this degradation is enhanced with regional climate change, with temperature and moisture being the key variables.…”