Melting glaciers, such as those in the Ilulissat Icefjord, can trigger significant methane releases.
Gerald Wetzel, Karlsruhe Institute of Technology, Germany
Increasing alarms are being sounded over the potential for melting glaciers to unleash tremendous quantities of greenhouse gases, particularly methane. Recent studies indicate that meltwater is releasing frozen methane hydrates from sediments along the Greenland ice sheet’s edge, a phenomenon reminiscent of patterns observed during the last glacial maximum between 29,000 and 19,000 years ago.
Methane hydrate is created when gas molecules become entrapped within a structure of frozen water molecules, creating what resembles ice, often referred to as “fire ice.” Despite being composed of 85% water, these hydrates pose significant environmental concerns. Burning them could release vast amounts of methane.
These hydrates form under high-pressure and low-temperature conditions present in oceans, permafrost, or beneath glaciers. Some estimates suggest that methane hydrates could hold double the carbon content of all the earth’s coal, oil, and natural gas combined.
However, global warming is altering the cold, high-pressure conditions where methane hydrates exist. For instance, a mystery crater discovered on the Arctic ocean floor in 2014 was believed to have been caused by melting permafrost, which suddenly released pressure on methane hydrates, resulting in a “violent physical explosion,” per the findings of a 2024 survey.
New research indicates that meltwater from Greenland’s glaciers can also release methane hydrates. “We found a new mechanism for releasing methane that was previously thought to be stable,” said Dr. Mat’s Houuse, who led the study from the University of Manchester, UK.
Dr. Hughes and colleagues identified that methane hydrates frequently accumulate between sediment grains at the bottom of Melville Bay in northwestern Greenland. Seismic surveys by oil and gas companies noted 50 large pockmarks on the ocean floor, up to 37 meters deep, near grounding wedges where the last ice sheet once met the ocean floor.
Initially believed to be caused by iceberg movements, investigations through sediment core samples revealed the top sediment layer had minimal methane, despite ideal methane hydrate conditions. The findings indicated substantial fresh water instead of expected seawater, likely due to ice sheet melt. Researchers hypothesize that during the last glacial maximum, meltwater flowing under Melville Bay’s glaciers pushed out methane hydrates through the grounding wedge.
As other glaciers continue to recede under climate change, melting could similarly wash away hydrates at the edges of additional glaciers, posing a significant risk. “In the near past, perhaps 12,000 to 15,000 years ago, there was a considerable methane release. The same could occur tomorrow or in the next century with ongoing ice sheet retreat,” warns Dr. Hughes. “Such events carry alarming implications since we’ve never accounted for them before.”
While the study does not quantify the methane released in Melville Bay, estimates suggest it could be around 130 million tonnes, equating to around two years of fossil fuel emissions. However, Dr. Hughes notes this methane could have been released over a century, rather than in a short timespan, making it a monumental yet singular event.
Additionally, methane dissolves in seawater, and not all of it may escape into the atmosphere, contingent on its saturation levels.
The Antarctic ice sheet likely contains even more methane hydrate than Greenland. Within polar regions, estimates suggest that between 100 billion and 760 billion tonnes of methane are potentially stored in subglacial and ocean hydrates. Even a small release could rival the 48.7 million tonnes of methane currently emitted annually from Arctic and boreal regions, predominantly from wetlands, lakes, and rivers, and could significantly exacerbate climate change.
Methane is already emanating from beneath the Greenland ice sheet. A recent study suggests that snowmelt across western Greenland contributes about 715 tonnes of methane each year. While some may derive from hydrates, it’s more likely to result from ancient plant material transformed into methane gas by bacteria beneath the ice, according to researcher Jade Hutton. This trend could escalate.
“If melting intensifies, it may tap into subglacial regions housing preserved organic carbon stocks that can easily convert to methane,” Hutton states. “This could lead to sizeable future releases.”
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Source: www.newscientist.com
