| Climate warming impacts on old carbon emission from subarctic peat soils
Among the largest uncertainties in current projections of future climate is the feedback between the terrestrial carbon cycle and climate. Northern peatland soils are rich in organic carbon and store an equivalent of more than half the amount of carbon in the atmosphere. Boreal and arctic permafrost soils together store 1670 billion tons of soil C, equivalent to twice the current amount in the atmosphere. Peatlands cover about 12% of Sweden and are especially abundant in the north. Northern high latitudes will experience above average climate warming, which may accelerate decomposition of these large, old carbon stocks and increase emission of CO2 into the atmosphere. This would cause a strong, positive feedback to the climate system. The size of this feedback is, however, uncertain, because the sensitivity of old carbon to increasing temperatures remains poorly understood and because permafrost processes and highly organic soils such as peat soils are poorly described in coupled carbon-cycle-climate (C4) models used for current climate projections. The response of northern soils to climate change is therefore a priority area for future research.
Sustained positive feedback to the climate requires accelerated emission of old soil carbon, which forms the bulk of the carbon pool in peatland and permafrost soils and has accumulated over thousands of years. However, the long-term effect of climate warming on soil carbon respiration has been debated for more than a decade and still remains controversial, because of high spatial variability and methodological challenges related to accurate in situ measurements, especially of the temperature sensitivity of old carbon at greater depth. The proposed research therefore aims to quantify the impact of climate warming on the release of CO2 from old carbon stores in subarctic peat-soils into the atmosphere.
To address our objective, we will use two established climate manipulation experiments in subarctic permafrost areas, one in north Sweden and one in Alaska. We will partition the components of respiration using a non-disturbing dual isotope (13C and 14C) approach, a newly developed, powerful tool to fingerprint the sources and age of the respired carbon. We will thus quantify in situ the increase in CO2 emission from old carbon in response to long-term experimental climate warming of a subarctic permafrost peatland in north Sweden. Furthermore, we will assess the spatial variability of these responses at a pan-Arctic scale by comparing the climate sensitivity of old carbon respiration in two important permafrost carbon reservoirs, subarctic peatlands (Sweden) and tussock tundra (Alaska). The proposed project will therefore make an important contribution to assessing the vulnerability of northern peatland and permafrost ecosystems within and outside Sweden and potential future carbon emissions.
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