Methane escapes from the bottom of the glaciers

Du méthane s’échappe du dessous des glaciers

Photo: John Sonntag / NASA / Agence France-Presse
Large reserves of methane are located under the glaciers of Greenland.

Under the thick ice in greenland, a source of methane. Micro-organisms in the sediments produce a powerful greenhouse gas that rivers sub-glacial tunnels to the atmosphere, confirmed Wednesday, a study published in the prestigious scientific journal Nature. Until now, the contribution of natural was not considered by the scientists.

“For the first time, we have continuously measured the concentration of methane of a river from the bottom of a glacier,” said Guillaume Lamarche-Gagnon, the lead author of the study. Previously, ” a few samples had been collected here and there “, but it was not possible to verify a trend of long-term issuance, ” says the phd candidate in geography at the University of Bristol, United Kingdom.

Du méthane s’échappe du dessous des glaciers

Photo: Mary Bulinova
The quebec researcher Guillaume Lamarche-Gagnon deploys a unit of measurement of methane such as the one used for his research in Greenland.

The young Quebecer and his colleagues have installed a probe in a river at the mouth of the glacier Leverett, which covers a drainage basin of 600 km2 in the south-west of Greenland. For a good part of the summer of 2015, from mid-may to mid-July, they registered a methane concentration supersaturated relative to the atmosphere — which means that the gas tends to be emitted into the air as soon as the water emerges from the depths of the glacier.

The researchers have measured that about six tonnes of methane are passed to the glacier Leverett during the summer of 2015. Of the lot, two or three tons “at a minimum” have been released into the atmosphere, the rest mixing with the ocean.

“The concentration of carbon is not huge compared to what is produced in a swamp, for example, says Mr Lamarche-Gagnon. But there’s so much water ! When you consider the total volume, it makes a huge amount of methane. “

Besides, the rocky bottom and the ice dynamics are similar elsewhere in Greenland, suggesting that it is possible to extrapolate the emissions of methane at the perimeter whole of the island.

To quantify the total impact, ” research in motion said the Quebecers. When we look at the budget of methane from the Arctic, the attention is especially directed to the permafrost. The sediment sub-glacial are not considered a source. Yet, they represent a contribution is probably significant. “

Studies like the one published this week, “are vital steps to improve our understanding of the sources and sinks of methane in the Arctic, and to improve our estimates of their future evolution,” wrote Lauren C. Andrews, a researcher at NASA, in a commentary accompanying the publication of the study.

And the Antarctic ?

As astonishing as it may seem, these are micro-organisms that produce the methane.

Under the kilometre-thick glacier to Leverett, microbes consume the carbon in organic matter, which is based there for thousands of years, and they release methane (CH4).

In summer, the ice and snow melt at the surface of the ice sheet.

“The melt water enters the ice through cracks and holes called “moulins”, until you reach the bedrock, ” says Mr Lamarche-Gagnon. Here, the melt-water is mixed with water, under-ice methane-rich. “

The mixture of water and walks then through a drainage system is highly developed, until at the end of the glacier, where it empties into a river.

Of course, it can be assumed that a melting of the ice sheet in greenland due to climate change will result in a larger discharge of methane. However, the proof remains to be done, believes Mr. Lamarche-Gagnon. The melt-water surplus could also simply further dilute the methane produced in the sediments, sub-glacial, not increasing the total amount of gas released.

And then, the “big question” is on the other side of the Earth, think of the biogéochimiste, where a huge ice sheet covers the continent of antarctica. The sediment sub-glacial are more conducive to the production of methane by micro-organisms. However, the mechanisms of flow of water under the ice are less well understood than Greenland.

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