Another feedback effect in the climate change system is emerging, researchers report: where the Arctic glaciers are retreating, groundwater gushes out of the exposed subsoil, releasing enormous amounts of the strong greenhouse gas methane. This is shown by investigations in the retreat area of glaciers in Spitsbergen. It is a significant and growing factor in climate processes that should now be included in calculations, the scientists say.
Fossil burning, agriculture and environmental degradation: Humans are still responsible for the gigantic releases of gases that lead to global warming. But as is becoming increasingly clear, the problem is fatally compounded by feedback loops. The anxious gaze is particularly focused on the underground reserves of methane in the Arctic caused by cold and pressure. So far, the focus has been on the increasing release of this particularly strong greenhouse gas as the permafrost melts. But the researchers led by Gabrielle Kleber from the University of Cambridge are now drawing attention to an effect caused by the retreat of glaciers in the Arctic.
Focus on groundwater sources
The scientists' results are based on investigations in the retreat area of glaciers on the Spitsbergen archipelago in the Arctic Ocean. The effect of climate change is particularly noticeable there: the numerous glaciers in the archipelago have retreated significantly in recent decades. As the researchers report, a striking number of springs bubble up from the underground in the uncovered areas. These are fed by groundwater that originates from sediments and rocks that were previously under the influence of the respective glacier. It was therefore to be assumed that methane previously bound by cold and pressure was increasingly getting into the water and could reach the surface via the springs and thus into the atmosphere.
To explore the magnitude of this effect, the team studied the water chemistry of more than a hundred springs at 78 glaciers in Svalbard. In some cases, the researchers were able to locate these with the help of satellite images because, as they explain, the exit areas are made clear by certain ice structures in the retreating areas of the glaciers. They were able to drive to the springs with snowmobiles to take water samples.
Bubbling climate danger
The results of their analysis revealed that the spring water is sometimes extremely enriched with methane, which can then escape. The concentration of the dissolved gas in the water can therefore be up to 600,000 times higher than in the atmosphere. The scientists were also able to link the respective extent of the methane content with local characteristics of the rock from which the groundwater in the retreat area of the glaciers feeds. Certain formations, which are characterized by slate, for example, contain a particularly large amount of methane and then release it into the groundwater via cracks.
Based on their results, Kleber and her colleagues estimate that around 2,000 tons of methane bubbles out of the groundwater sources of glacier forelands throughout Spitsbergen every year. According to them, this suggests that the effect is of great importance: Since many other regions in the Arctic region are affected by a glacier retreat and the process continues to intensify, it could be a significant and growing factor in climate events, say the scientists.
"There is evidence that these sources can be a significant and potentially growing source of methane emissions that have not previously been accounted for in estimates of the global budget for this greenhouse gas," Kleber concludes. Co-author Alexandra Turchyn from the University of Cambridge says: "While the focus is often on permafrost, this new result now shows us that there are also other pathways for methane emissions that could be important for the global methane balance." the scientist.
Source: University of Cambridge, professional article: Nature Geoscience, doi: 10.1038/s41561-023-01210-6