Ethyl and methyl alcohols released when permafrost thaws are processed by bacteria from the upper soil layers, but will this slow down the rate of global warming?
When they talk about the impact of global warming on the Arctic, many see the danger primarily in melting ice and rising sea levels, as well as in the difficult future of polar bears. However, there is another process that causes serious concern – the thawing of permafrost. The problem is that frozen ground contains large volumes of gases and volatile organic compounds, which could begin to enter the atmosphere if the permafrost ceases to be permafrost.
Melting permafrost caused by climate change could release large amounts of greenhouse gases into the atmosphere. Photo: Rose Cory, University of Michigan/Flickr.com
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Once released into the atmosphere, such compounds can trigger the formation of aerosols and greenhouse gases, which will accelerate the already high rate of climate change. An attempt to understand the processes that will occur with permafrost if it does melt was made by a group of European researchers. The object of study was soil samples taken from the permafrost zone in Greenland.
The researchers collected two types of soil: one from the depths, where constant subzero temperatures persist, and others from the surface, which periodically thaws during the short arctic summer. This was necessary in order to understand what would happen to volatile organic substances when they were released from melting layers at depth and began to seep closer to the surface. The fact is that the upper layers of the soil are saturated with various microorganisms, which begin active activity as soon as the soil temperature changes from minus to plus. And it is quite possible that they can feed on substances coming from below.
It is also worth mentioning where volatile organic substances appear in frozen soil. Despite the fact that the temperature of these layers does not rise above 0 °C for years, or even millennia, some microorganisms have adapted to remain active even in such unfriendly conditions. Bacterial waste products will gradually accumulate in frozen soil until soil thawing causes their rapid release.
As for the chemical composition of the “exhalation” of Greenlandic permafrost, it is very unusual. More than half of it consists of ethyl alcohol, followed by methyl alcohol, acetaldehyde, acetone, formaldehyde and about three hundred more organic compounds – at least that much was found in the samples. If this flow of substances is passed through a layer of soil taken from the surface, then almost the entire volume of volatile substances will be absorbed and processed by the microorganisms inhabiting it.
Interestingly, ethanol and methanol, the two main volatile organic compounds, are used differently by bacteria in the topsoil. They convert almost all methanol into carbon dioxide, which suggests that bacteria use it as an energy source. But bacteria use ethyl alcohol primarily as a source of carbon for growth and synthesis of necessary substances.
It may seem that the results of the study allow us to not worry so much about thawing permafrost, since bacteria in the upper layers of the soil, as it turned out, can easily eat almost anything that seeps from the thawing ground. However, this is not quite true.
Firstly, bacteria will convert most of the compounds into carbon dioxide, which will somehow enter the atmosphere. Secondly, with rapid melting, bacteria may simply not be able to cope with the incoming volume of organic matter, since they need time to process it and time to simply have time to reproduce. In addition, it is not at all necessary that volatile organic matter from melting soil will necessarily pass through the layer of biologically active soil, and not directly enter the atmosphere.
Based on materials from Nature Communications