Abstract
Permafrost thaw increases active layer thickness, changes landscape hydrology and influences vegetation species composition. These changes alter belowground microbial and geochemical processes, affecting production, consumption and net emission rates of climate forcing trace gases. Net carbon dioxide (CO2) and methane (CH4) fluxes determine the radiative forcing contribution from these climate-sensitive ecosystems. Permafrost peatlands may be a mosaic of dry frozen hummocks, semi-thawed or perched sphagnum dominated areas, wet permafrost-free sedge dominated sites and open water ponds. We revisited estimates of climate forcing made for 1970 and 2000 for Stordalen Mire in northern Sweden and found the trend of increasing forcing continued into 2014. The Mire continued to transition from dry permafrost to sedge and open water areas, increasing by 100% and 35%, respectively, over the 45-year period, causing the net radiative forcing of Stordalen Mire to shift from negative to positive. This trend is driven by transitioning vegetation community composition, improved estimates of annual CO2 and CH4 exchange and a 22% increase in the IPCC's 100-year global warming potential (GWP_100) value for CH4. These results indicate that discontinuous permafrost ecosystems, while still remaining a net overall sink of C, can become a positive feedback to climate change on decadal timescales.This article is part of a discussion meeting issue ‘Rising methane: is warming feeding warming? (part 2)’.
Highlights
Accelerated climate warming in the Arctic has led to permafrost thaw which results in a deeper active layer, changes in soil moisture and hydrology and subsequent vegetation community shifts [1,2,3]
We present an updated vegetation composition dataset and an improved estimate of annual CO2 and CH4 exchange rates to present a time series of trace gas radiative forcing for the Stordalen Mire, a permafrost peatland located in the discontinuous permafrost zone of Northern Sweden
Using an artificial neural network (ANN) and unmanned aerial systems (UASs) imagery collected at Stordalen Mire in 2014, a previous study developed a landcover map focused on vegetation cover types representing permafrost thaw stages [11]
Summary
Accelerated climate warming in the Arctic has led to permafrost thaw which results in a deeper active layer, changes in soil moisture and hydrology and subsequent vegetation community shifts [1,2,3]. Permafrost peatlands are a mosaic of frozen hummocks or palsas, semi-thawed sphagnum dominated areas or bogs, fully thawed sedge dominated areas or fens and often small open water ponds formed through the collapse of permafrost [1,9] Monitoring changes in these sub-habitats is critical to partitioning and quantifying the climate forcing fluxes from this region. For open water surfaces too small for eddy covariance techniques, like those often found in thawing environments, estimates of the rate of hydrodynamic advection of trace gases are measured directly using floating chambers [18,19] or by estimating fluxes using dissolved concentration measurements in combination with transfer coefficients [20,21] Ebullition or bubbling, another potentially dominant transport pathway of CH4 emission from ponds, is measured using bubble traps distributed across the water surface [22,23]. We present an updated vegetation composition dataset and an improved estimate of annual CO2 and CH4 exchange rates to present a time series of trace gas radiative forcing for the Stordalen Mire, a permafrost peatland located in the discontinuous permafrost zone of Northern Sweden
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