01.09.2017: Wide areas of sea floor in arctic shallow waters consist of permafrost. So far, little is known about how microorganisms in these soils below sea level react on increased warming. Scientists of the Helmholtz Young Investigators group MicroCene, led by Susanne Liebner, GFZ section Geomicrobiology, now investigated the microbial communities of two Siberian submarine permafrost cores. They show that the microbes become increasingly active, although with an extensive time lag.

The study area is located in the Laptev Sea in east Siberia, where more than 80 percent of the global submarine permafrost are expected. There, the Alfred Wegener Institute for Polar and Maritime Research, AWI, together with Russian partners from the Melnikov Permafrost Institute Yakutsk sampled permafrost cores. Initially, these permafrost soils were formed on land. However, about 15,000 years ago, after the end of the last glacial phase, a rising sea level inundated the frozen soils that today lie below sea level. One of the investigated cores was flooded 2,500 year ago, the other one about 540 year ago. The results, published in the Journal of Geophysical Research: Biogeosciences, are nowdistinguished as a “research spotlight” by the news platform EOS of the American Geophysical Union AGU. With this, EOS honors “the best accepted articles” that were published in an AGU journal.

Submarine permafrost is more sensitive to climate warming than permafrost on land thus thawing faster. This is due to the fact that water transports heat more effectively than air and due to the fact that the salty sea water reduces the dew point. This is also the reason why salt is spread on roads during winter time. What does this mean for the soil microbiome? Liebner: “The arctic coasts are severely affected by global warming. Rising sea levels and collapsing coastlines caused by thawing permafrost result in extreme environmental change. How the soil microbiome is reacting is largely unknown so far.”

To get answers to this question the team of first author Julia Mitzscherling interpreted samples that were analysed at the AWI, and investigated the pore water within the permafrost soils as well as traces of microbial genetic material found in the soils. The time span between inundation of both cores as well as their stratigraphic composition helps to assess how the microbial communities develop through time. Mitzscherling: „Based on changes between the two cores we were able to show that a reaction of the microbial communities on the warming in form of changes in the composition of their communities and probably growing is only seen in millennia after flooding. Apparently, it takes a lot of time until a serious reaction on environmental change sets in.“

It is however the most likely future scenario for large parts of submarine permafrost areas that the microbes in the permafrost soils awake from „ice-age hibernation“, and mobilise the previously frozen carbon. The fate of the mobilized carbon needs to be investigated by further studies. (ak)

Original study: Mitzscherling, J., Winkel, M., Winterfeld, M., Horn, F., Yang, S., Grigoriev, M.N., Wagner, D., Overduin, P.P., Liebner, S., 2017. The development of permafrost bacterial communities under submarine conditions. Journal of Geophysical Research: Biogeosciences 122, pp. 2169-8961. DOI: 10.1002/2017JG003859

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