Rising permafrost temperatures raise emission of the climate relevant trace gas methane

Higher temperatures in Arctic permafrost soils alter the community of methane producing microorganisms and lead to an increased emission of methane. Microbiologists from the Alfred Wegener Institute come to this conclusion in the current issue of the periodical “Environmental Microbiology”.

The scientists were able to examine permafrost from the ground of the Laptev Sea, a shallow shelf sea close to the coast of Siberia, for the first time. Caused by overflooding with relatively warm sea water, this so-called “submarine permafrost” is about 10° C warmer than the permafrost on land. It is therefore particularly suited to monitor changes in permafrost soils caused by continuing heating of the earth's atmosphere.

“If the permafrost soils grow warm or even thaw, dramatic consequences for worldwide climate events might occur,” illustrates the microbiologist Dr. Dirk Wagner from the Potsdam Research Unit of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association the importance of permafrost research. “They cover about 25% of the earth's land area and store huge amounts of organic carbon.”

Under the exclusion of oxygen and therefore under conditions typical of permafrost due to water saturation, the climate relevant trace gas methane is generated by decomposition of organic carbon. Special microorganisms are responsible for the generation of methane, called methanogenic archaea. “How much carbon is transformed and how much carbon is accordingly generated depends on the metabolic activity of the organisms and on the composition of the microbial community”, explains Wagner. “We are therefore engaged in the question how these two parameters change under rising temperatures in permafrost.”

The researchers were already able to show in former studies that microorganisms generate methane even in deeply frozen permafrost layers of about -7° C. If these temperatures are experimentally increased by some degrees, the organisms' metabolic activity increases and thus also the production of methane in permafrost. It has so far not been clarified, however, whether the community of methane producing microorganisms would be able to permanently adapt to higher temperatures in permafrost soils. The researchers from Potsdam were able to provide evidence by their comparison of terrestrial and submarine permafrost layers.

Submarine permafrost has developed in a former landmass which was flooded due to the raised main sea level after the last glacial. It is therefore originally a terrestrial permafrost deposits. In contrast to current terrestrial permafrost with a mean temperature of -12° C, submarine permafrost has already been warmed to a temperature of -2° C. By comparing the two communities of microorganisms generating methane in both permafrost regions, Wagner and his team were able to show that the composition of methane producing microorganisms in submarine permafrost is clearly distinguishable from terrestrial permafrost. The community is therefore able to adapt well and permanently to rising temperatures.

“The studies we were conducting during the last ten years in the vicinity of the Russian-German research station Samoilov in the Siberian Arctic show clearly”, summarises Wagner the insights of his long years of work “that the communities of microorganisms react flexible to climate change. Even if the soil is still deeply frozen, the metabolic activity of methane producing microbes is increased with rising temperatures. It is definite evidence for us that the atmospheric warming we can observe leads to an increased emission of the climate relevant trace gas methane in earth's vast permafrost regions even today.”

The Alfred Wegener Institute carries out research in the Arctic and Antarctic as well as in the high and mid latitude oceans. The institute coordinates German polar research and provides international science with important infrastructure, e.g. the research icebreaker Polarstern and research stations in the Arctic and Antarctic. The Alfred Wegener Institute is one of 15 research centres within the Helmholtz Association, Germany's largest scientific organization.