A recent study led by researchers from the University of Eastern Finland reveals that permafrost thaw may greatly increase emissions of nitrous oxide (N 2 O) from northern permafrost peatlands. Nitrous oxide is a strong greenhouse gas: 300 times more powerful per unit mass in warming the climate than CO 2 . 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 (CO 2 ) and methane (CH 4 ). The role of N 2 O for permafrost-climate feedbacks, however, is not yet well understood.

The study was published in the journal Proceedings of the National Academy of 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 N 2 O 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 N 2 O 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 N 2 O source. The presence of vegetation cover in the mesocosms lowered thaw-induced N 2 O emissions by approximately 90%. Water-logged conditions completely suppressed the N 2 O emissions. A vulnerability assessment indicated that areas with high probability for N 2 O emissions cover approximately one fourth of the Arctic. According to the authors, the Arctic N 2 O budget will depend strongly on future moisture and vegetation changes. However, the authors state that the Arctic will likely become a substantial source of N 2 O 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.