Study of Alaska's permafrost reveals new secrets

It was a rather special return to Belgium for Sophie Opfergelt, Maëlle Villani and Sébastien François (ELI-E). From 11 to 27 March, the team was in Eight Mile Lake, Alaska (USA), for a cold but intense expedition to study permafrost.

However, this was not the first trip organized with this objective in mind. Since 2018, 7 missions have already been carried out. But this one had a special feeling for the team, who brought back  water from no fewer than 48 river ice and soil cores for analysis. 

The objectives of the expedition were part of Maëlle Villani's doctoral thesis. She is an FNRS researcher at the Earth and Life Institute, studying the impact of the thawing of the permafrost in winter. The aim was to observe the ‘taliks’, the portions of soil that remain thawed all year round, even in winter, when the entire ground should normally be frozen at this time of the year.

A dangerous unplug of the freezer

“In recent years, global warming has caused temperatures to rise, which has a direct impact on permafrost”, explains Maëlle Villani. “In 2019, an extreme summer record of 32°C was recorded in Alaska. This heat causes the ground to thaw to such a depth that it no longer refreezes completely in winter. So, we end up with sections that never freeze again”, adds Sophie Opfergelt, FNRS Senior Research Associate in geochemistry and head of the Alaska expeditions.

But in soil that contains water rather than ice, microbial activity is observed to resume, decomposing soil organic matter. “If these taliks are isolated, there are ultimately fewer implications for carbon loss, continues Maëlle Villani. But if the taliks are interconnected, underground water pathways may appear, with potentially a lateral carbon loss from soils.”

The team went out to investigate whether these taliks, which are still much debated in scientific literature, could really be observed, and whether there were many of them. They drilled in very specific places, determined thanks to previous expeditions in the projects LandSense and LIFTHAW, to retrieve soil cores. The analysis will focus on the chemistry of the water in the taliks and should determine what is released into the soil in winter according to a degradation gradient.

In the meantime, the team's observations are already clear: “We saw that there were a lot of taliks, much more than we thought”.

A lot of luck with the weather

Despite these alarming observations, Sophie, Sébastien and Maëlle underline the success of the mission. “We were very well prepared, we got on well together, our skills were very complementary, which enabled us to work efficiently, and we were lucky with the weather.” Despite very cold temperatures, the team benefited from blue skies most of the time. “We've been very fortunate. No snowstorms and some magnificent northern lights.”

Sébastien François, a member of the ELI-E research support unit and a specialist in soil sampling techniques, also recalls a particularly memorable moment: an unexpected encounter with a moose that crossed the trail just a few dozen meters ahead as they were heading to the study site by snowmobile. The team stopped briefly to capture the moment before continuing on their way to the site.

The success of such a mission is never guaranteed. Bad weather, stress, illness, fatigue, or equipment failure: many unforeseen events can occur. “It's a very challenging mission, but it's also an incredible experience.”

The next mission is already scheduled for September 2025. It will help to quantify the thawing of the permafrost by comparing the measurements that will be made with the same measurements made in 2023.

Article: Emmeline Van den Bosch

Photos: Sophie Opfergelt, Maëlle Villani, Sébastien François