Rapidly retreating Arctic glaciers may be setting off a dangerous climate feedback cycle, with new research suggesting that meltwater is drawing ancient methane from rocks long buried beneath the ice.
The findings come from an analysis of 148 water samples taken from 19 glacier-fed rivers across Svalbard, the remote Norwegian archipelago located deep in the Arctic Ocean.
Scientists found that every river they tested contained methane concentrations higher than levels expected from simple exposure to the atmosphere.
In the most extreme cases, methane levels were as much as 425 times greater than normal, highlighting the scale of the hidden emissions being released through Arctic waterways.
Methane is a highly potent greenhouse gas, and when it escapes from rivers into the air it adds to global warming—potentially accelerating the very glacier melt that is helping release it.
As the planet warms and glaciers melt faster, more methane will be released, leading to yet faster warming and even greater melting.
Lead author Dr Gabrielle Kleber, a researcher with the iC3 Polar Research Hub, says: ‘The amounts reported here are small compared with human–caused emissions from fossil fuels, farming and waste.
‘But they matter because they reveal a natural feedback loop that is not confined to Svalbard, and that may grow as the Arctic warms.’
Melting Arctic glaciers are creating a ‘doom loop’ by flushing methane out into rivers. Pictured: A glacial river on Svalbard
Importantly, the researchers found that this methane is not being created by microbes under the ice, as has been found to be the case in Greenland.
The teamanalysed the types of carbon found in the water, revealing that many contained propane and ethane in addition to methane.
This is exactly what you would expect to find if the methane has a geological source, rather than a biological one.
Many parts of the Svalbard archipelago contain layers of old shale rock that is rich in organic carbon.
Over millions of years, heat and pressure beneath the ground can transform this carbon into methane as well as other gases like propane and ethane.
Dr Kleber says: These glaciers are mostly melting on their surfaces, but this meltwater finds its way to the bottom of the glaciers through crevasses and holes.
‘This means that it interacts with the rocks underneath, and where those rocks contain ancient gas, the water can flush methane out into rivers.’
The researchers estimate that land–terminating glaciers across Svalbard may transport roughly 182 to 368 tonnes of methane per year in meltwater.
Scientists used water samples and ground–penetrating radar measurements (pictured) to show that water from melting glaciers is flushing out ancient methane from the rocks below
This is particularly worrying for the Arctic because methane is an especially powerful greenhouse gas.
Over 100 years, a kilogram of methane is 21 times more effective than a kilogram of CO2 at trapping heat in the Earth’s atmosphere.
That is in addition to previous, much higher estimates for the amount of methane being released by groundwater springs in front of glaciers.
Using ground–penetrating radar, the researchers also mapped the ice conditions in some of the glaciers to see which factors led to the highest methane emissions.
The most methane–rich waters tended to come from glaciers resting on rich seams of shale, but the state of the glacier itself also played a major role.
Co–author Leonard Magerl, from UiT The Arctic University of Norway, says: ‘The temperature at the base of glaciers is an important piece of the puzzle.
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‘We found that the biggest methane releases happened where the right rocks and the right glacier conditions came together.’
The big concern is that this additional boost of greenhouse gases will accelerate the already rapid melting of Arctic glaciers and cause yet more methane to be released.
Some rivers had up to 425 times the levels of methane that would be expected if they were simply absorbing the greenhouse gas from the atmosphere. Pictured: Scientists take a sample from a glacial river on Svalbard
Previous studies have shown that Arctic glaciers like the Geikie Plateau in eastern Greenland (pictured) contain almost twice as much ice as previously estimated, creating a significant risk that rapid melting will raise sea levels significantly
As glaciers retreat and thin, more meltwater may reach their beds and come into contact with fractured rock, sediment and groundwater, flushing out more methane.
If that does lead to accelerated melting in the Arctic, the resulting sea level rise could trigger severe consequences for the rest of the world.
The Greenland Ice Sheet, which sits within the Arctic Circle, contains enough fresh water to raise sea levels by 23 feet (7.4m) if it were to melt entirely.
With recent research estimating that more than 100 million people currently live below sea level, this could cause a catastrophic displacement of people from coastal regions.
However, the researchers aren’t yet totally sure whether this cycle will keep on accelerating into the future.
Some Svalbard glaciers are actually getting colder at their bases as they shrink and melt at the surface.
If a glacier becomes frozen to the bedrock, its ability to flush methane out into rivers could diminish.
Dr Kleber adds: ‘Our results show that future methane release will depend on both geology and glacier change. That makes it important to know what lies beneath the ice, not only how fast the ice is melting.’