Date: February 29, 2024
Source:
University of Copenhagen - Faculty of Science
Summary:
Global melting is prying the lid off methane stocks, the extent of which we do not know. A researcher has now discovered high concentrations of the powerful greenhouse gas in meltwater from three Canadian mountain glaciers, where it was not thought to exist -- adding new unknowns to the understanding of methane emissions from Earth's glaciated regions.
Global melting is prying the lid off methane stocks, the extent of which we do not know. A young researcher from University of Copenhagen has discovered high concentrations of the powerful greenhouse gas in meltwater from three Canadian mountain glaciers, where it was not thought to exist -- adding new unknowns to the understanding of methane emissions from Earth's glaciated regions
The helicopter's rotor blades spin as its skillful pilot performs aerial acrobatics between the steep Yukon mountain sides where PhD student Sarah Elise Sapper is leading her first field expedition deep into the heart of the mountains of northwestern Canada. From the helicopter windows, her eyes fall on the jagged edge of the Donjek glacier: meltwater swirls out from beneath the ice like a whirlpool.
Soon after landing, it becomes apparent that Sarah has stumbled upon an unusual find on the first attempt. Seconds after starting up her portable methane analyzer it is clear that the air is enriched with methane and the culprit is soon found. Collecting a sample of meltwater, she measures concentrations of methane that far exceed expectations.
"We expected to find low values in the meltwater because it is believed that glacial methane emissions require larger ice masses such as vast ice sheets. But the result was quite the opposite. We measured concentrations up to 250 times higher than those in our atmosphere," explains Sarah Elise Sapper of the University of Copenhagen's Department of Geosciences and Natural Resource Management.
The field party lifted off and continued to two more mountain glaciers, Kluane and Dusty. And after measuring the methane in the meltwater of each of those two glaciers, the preliminary finding turned out to be more than an anomaly. Here too, measurements showed high methane concentrations. Somewhere beneath the ice, there are previously unknown sources of the gas.
Demonstrates possibility of widespread methane emissions
"The finding is surprising and raises several important questions within this area of research," says Associate Professor Jesper Riis Christiansen of the Department of Geosciences and Natural Resource Management.
Christiansen, the research article's co-author, believes that the finding demonstrates the possibility of methane being present beneath many of the world's glaciers, ones that have thus far been written off.
"When we suddenly see that even mountain glaciers, which are small in comparison with an ice sheet, are able to form and emit methane, it expands our basic understanding of carbon cycling in extreme environments on the planet. The formation and release of methane under ice is more comprehensive and much more widespread than we thought," he says.
Until now, the prevailing view has been that methane in meltwater could only be found in oxygen- free environments under large masses of ice like the Greenland Ice Sheet.
The researchers assume that the production of methane is biological and happens when an organic carbon source -- e.g., deposits from prehistoric marine organisms, soils, peat or forests -- is decomposed by microorganisms in the absence of oxygen, such as we know from wetlands. As such, it is surprising that the mountain glaciers emit methane.
"The meltwater from the surface of glaciers is oxygen-rich when it travels to the bottom of the ice. So we found it quite surprising that all this oxygen is used up somewhere along the way, so that oxygen-free environments form underneath these mountain glaciers. And even more surprising that it happens to such a degree, that microbes start producing methane and we can observe these high methane concentrations in the water flowing out at the glacier edges" states Sarah Elise Sapper.
"Sarah's findings change our basic understanding and send us back to the drawing board in relation to some of the key mechanisms at play," adds Jesper Riis Christiansen.
An uncertain role for the climate of the future
According to the researchers, the findings in Canada do not immediately spur an increased concern in relation to their effect on climate change. However that conclusion may be temporary.
"Methane plays a major role in warming our planet. The challenge with methane is that it is a super-potent greenhouse gas and increasing emissions will accelerate climate warming. From a global perspective, we can measure how much is emitted into the atmosphere and, roughly speaking, where the methane comes from, using the isotopes found in the atmospheric methane. And for now, the contribution of methane from ice-covered regions on our planet, including ice sheets and glaciers, isn't increasing," explains Jesper Riis Christiansen.
However, he emphasizes that the measurements cannot distinguish between methane from glaciated regions and methane from wetlands. Therefore, the numbers could be deceiving. And, the effect of melting remains unknown.
Jesper Riis Christiansen believes that the findings demand vigilance.
"The three sites Sarah measured were randomly selected due to the availability of a research station and helicopter, yet methane was found in all three. In itself, that is a good reason to better understand the area. There's too much that we don't know, and the melting glaciers expose unknown environments that have remained hidden for thousands of years. In reality, no one knows how emissions will behave," says Jesper Riis Christiansen.
He hopes that a better understanding of methane behaviour beneath glaciers will also help researchers better understand the mechanisms at play when wetlands release methane, and thereby contribute to the development of solutions to remove methane from the atmosphere through oxidation -- e.g., through the use of certain soil types.
A subglacial black box
The actual sources and locations of subglacial methane production actually remain somewhat of a mystery, hidden beneath ice masses of all sizes. Indeed, this methane can only be measured as the meltwater emerges from beneath the ice. And because it originates from large areas below the ice masses, this makes it difficult to access exactly where the production happens.
It is known to not originate from the ice itself, as concentrations both in the ice and meltwater atop it are lower than what is measured at the glacier edge. As such, the researchers believe that the methane must derive from a source beneath the ice. And the best theory, as mentioned, is that it is formed by microbes in oxygen-free pockets and then carried out with meltwater.
But this indirect knowledge of the source leaves a great deal of uncertainty about how much methane is hidden beneath the ice.
"It's a big black box under the ice -- and you could say that the meltwater is prying the lid off it. We do not know whether methane emissions from glacial areas will increase in the future with increased melting, or whether the 'lid' has already been opened to such a degree that the methane beneath the ice is actually being washed out with the meltwater," says Sarah Elise Sapper.
Methane and CO2 are different greenhouse gases
The half-life of methane in the atmosphere is 12 years.
CO2 has a much longer half-life, at roughly 1000 years.
On the other hand, methane is about 25 times more powerful as a greenhouse gas on a 100-year basis and a far more serious threat to global climate in the shorter term.
Due to greenhouse gas-driven climate change, researchers around the world are working to develop ways to capture or store CO2.
Similarly, solutions are being devised to limit the emission of -- or increase the oxidation of -- methane. Doing so requires more knowledge about how methane is formed.
Facts: Carbon circulation of methane and CO2
Biological traces from animal and plant material in the subsoil consist of carbon.
Within these environments, microorganisms have developed an ability to convert carbon into energy in a process where methane is created as a byproduct in the absence of oxygen (e.g. in beneath ice sheets or in wetlands)
However, if the methane is released into an oxygen-rich environment, it can effectively be oxidized and converted into CO2 by microbes. Wetlands play an important role in this process.
Once, in the atmosphere, methane reacts with other chemicals (hydroxyl radicals) which keep the concentrations down.
However, as temperatures rise, the amount of methane emitted from ecosystems around the world increases -- from the Arctic to the Amazon. And the balance may be shifting if the processes that remove methane do not react to the same degree.
Story Source:
Materials provided by University of Copenhagen - Faculty of Science. Note: Content may be edited for style and length.
Journal Reference:
Sarah Elise Sapper, Christian Juncher Jørgensen, Moritz Schroll, Frank Keppler, Jesper Riis Christiansen. Methane emissions from subglacial meltwater of three alpine glaciers in Yukon, Canada. Arctic, Antarctic, and Alpine Research, 2023; 55 (1) DOI: 10.1080/15230430.2023.2284456
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