Thawing Siberian permafrost appears to emit a surprising amount of laughing gas

The discovery underlines that it is not only CO2 and methane that leaks from the thawing soil; we should certainly not underestimate the emission of nitrous oxide.

We’ve been aware of a problem for a while now. Global warming is thawing permafrost: a previously permanently frozen soil that we mainly know from the Arctic region. This releases methane and carbon dioxide, which have been stored there for thousands of years. These gases, in turn, contribute to global warming. Researchers now come in a study to a new troubling discovery. Because thawing permafrost in Siberia turns out to be pumping yet another dangerous greenhouse gas into the atmosphere: nitrous oxide.

In the study, scientists examined the Lena and Kolyma rivers, located in northeastern Siberia. It is known that the permafrost along these riverbanks is rapidly wasting away. This exposes so-called ‘yedoma permafrost’: an organically rich permafrost that dates back to the Pleistocene era. This ancient frozen ‘mud’ thought it was safe here for thousands of years, but now appears to be thawing rapidly.

Nitrous oxide

Initially, this recently thawed yedoma emitted little nitrous oxide. But in less than a decade, the amounts being pumped into the atmosphere have suddenly increased very rapidly. New research even shows that nitrous oxide emissions are between 10 and 100 times higher than previously thought. And that while yedoma permafrost extends over more than a million square kilometers of land in the Northern Hemisphere. In particular, the high ice content of yedoma makes it vulnerable to an abrupt thaw, which releases a lot of nitrous oxide.

Farmland

It’s a remarkable discovery. We usually see high nitrous oxide emissions in agricultural soils, where the availability of mineral nitrogen is high. However, because the nitrogen cycle in cold Arctic soils is slow, nitrous oxide emissions in such areas were previously considered ‘negligible’. But nothing turns out to be less true. The evidence that nitrous oxide is released from permafrost soils is accumulating. Moreover, with global warming, disturbed vegetation and the thaw of permafrost, these emissions are increasing.

Warning

“This is an important warning of the potential climatic consequences,” said researcher Maija Marushchak in conversation with Scientias.nl. “That is because the emission of nitrous oxide can have a climate-warming effect.” But there is not all bad news. “On the other hand, it could potentially cool the climate as well,” Marushchak says. “That happens when the extra nitrogen that leaks from permafrost is effectively captured by plants, which in turn use it to grow and in the process absorb more carbon dioxide from the atmosphere. However, no one knows at this point which effect will be stronger.”

Grasses

It is striking that in the areas studied, nitrous oxide in particular escapes from thawed yedoma where grasses grow. “Although the plants there absorb a large part of the reactive soil nitrogen, we saw the highest N2O emissions here,” says Marushchak. “And that while in previous studies the highest N2O emissions were found in soils where no plants grow. This shows how extensive nitrogen is available in old yedoma sediments. In fact, it contains so much nitrogen that it exceeds the needs of microbes and plants. As a result, the remaining nitrogen in the atmosphere is lost. In addition, it ends up in rivers and lakes and even reaches the Arctic Ocean via an extensive Arctic river network. In short, nitrous oxide emissions are important as such, but the general implications go much further.”

What to do?

The question, of course, is whether we can do anything to prevent even more nitrous oxide from leaking from age-old and thawed permafrost. “Unfortunately, there are no direct ways to prevent permafrost from thawing in the vast, remote Arctic regions in order to reduce the associated greenhouse gas emissions,” Marushchak said when asked. “The only way to protect permafrost is if we manage to limit our own emissions from fossil fuel burning and land use. For N2O emissions specifically, we need to focus on agriculture. Agriculture is an important source of N2O and is mainly responsible for the increase in atmospheric N2O concentration in recent decades.”

All in all, the study is mainly a description of an observation. Much more research will need to be conducted in the future to map out how much nitrogen is stored in the cold, Siberian landscapes, how quickly nitrous oxide is released and what the effects could be on global warming and the ecosystems as a whole.