A recent study led by researchers from the University of Eastern Finland reveals that permafrost thaw may greatly increase emissions of nitrous oxide (N2O) from northern permafrost peatlands. Nitrous oxide is a strong greenhouse gas: 300 times more powerful per unit mass in warming the climate than CO2. It is known that thawing of permafrost may enhance climate warming by releasing the vast carbon stocks locked in Arctic soils as the greenhouse gases carbon dioxide (CO2) and methane (CH4). The role of N2O for permafrost–climate feedbacks, however, is not yet well understood.

The study was published in the journal PNAS (Proceedings of the National Academy of Sciences of the United States of America) – one of the top-level journals in natural sciences.

The authors used 16 mesocosms – 80 cm long, intact peat columns with natural vegetation – collected in a subarctic peatland in Finnish Lapland, to directly measure N2O emissions from thawing permafrost during a 33-week experiment. For this experiment, the mesocosms were set up in a climate-controlled chamber, mimicking natural temperature, moisture and light conditions. Sequential top-down thawing of the mesocosms – first of the seasonally thawing active layer and then the permafrost part – allowed the authors to directly assess N2O dynamics under near-field conditions.

The highest post-thaw emissions occurred from bare peat surfaces, which are commonly found in permafrost peatlands. For these surfaces, permafrost thaw resulted in a five-fold increase in emissions. The emission rates measured from these surfaces matched rates from tropical forest soils, the world’s largest natural terrestrial N2O source. The presence of vegetation cover in the mesocosms lowered thaw-induced N2O emissions by approximately 90%. Water-logged conditions completely suppressed the N2O emissions. A vulnerability assessment indicated that areas with high probability for N2O emissions cover approximately one fourth of the Arctic. According to the authors, the Arctic N2O budget will depend strongly on future moisture and vegetation changes. However, the authors state that the Arctic will likely become a substantial source of N2O when permafrost thaws.

The study was carried out by researchers of the Department of Environmental and Biological Sciences at the University of Eastern Finland, in cooperation with colleagues from Lund University, Sweden.

The research was funded by the Nordic Center of Excellence DEFROST, and supported by the European Union project PAGE21, the Academy of Finland (project CryoN), and JPI Climate project COUP.

Research article

Carolina Voigt, Maija E. Marushchak, Richard E. Lamprecht, Marcin Jackowicz-Korczyński, Amelie Lindgren, Mikhail Mastepanov, Lars Granlund, Torben R. Christensen, Teemu Tahvanainen, Pertti J. Martikainen, Christina Biasi (2017): Increased nitrous oxide emissions from Arctic peatlands after permafrost thaw. Proceedings of the National Academy of Sciences of the United States of America. http://www.pnas.org/content/early/2017/05/23/1702902114.full.pdf.

Source: University of Eastern Finland