Ilulissat Icefjord in western Greenland
Gerald Wetzel, Karlsruhe Institute of Technology, Germany
Following the last glacial maximum, meltwater has washed frozen methane hydrate from sediments along the edge of Greenland’s ice sheet, raising significant concerns about the potential release of this powerful greenhouse gas due to melting glaciers.
Methane hydrate forms when gas molecules are trapped within a lattice of water molecules and freeze into a solid, often referred to as “fire ice.” Despite being composed of 85% water, its flammability is notable.
This unique structure forms under high pressure and low temperature conditions found in oceans, permafrost, or beneath glacial sediments. Estimates suggest that methane hydrate may contain double the carbon found in all coal, oil, and traditional gas resources on Earth.
However, climate change is disturbing the cold, pressurized environments necessary for the stability of methane hydrate. For instance, some scientists suggest that a mysterious ocean floor crater discovered beneath the Arctic in 2014 was formed by the sudden release of pressure on methane hydrate due to thawing permafrost, described as a “violent physical explosion” in a 2024 study.
Recent research from Greenland indicates that methane hydrate can also be released by glacier meltwater flows. “We discovered a new release mechanism for methane that was assumed to be secure,” says Dr. Mat’s House from the University of Manchester, UK. “What we previously thought was stable is, in fact, methane.”
Hughes and his team recognized that methane hydrate is often found in spaces between sediment grains in Melville Bay, northwestern Greenland. Seismic surveys conducted by oil and gas companies during 2011 and 2013 revealed 50 large pockmarks on the ocean floor, some reaching depths of 37 meters, situated near long grounding wedges. These are locations where the floating ice sheet met the ocean floor during the peak of the last ice age.
Initially, researchers believed these pockmarks were caused by icebergs tipping over. However, drilling sediment cores in the area revealed that the upper sediment layer contained minimal methane, despite ideal temperature and pressure conditions for methane hydrate formation.
Moreover, significant amounts of freshwater were located in the sediment, contradicting the expected seawater findings, a situation only possible due to recent ice sheet melting. The research indicates that during the last glacial maximum, meltwater flowing under glaciers in Melville Bay likely passed through the grounding wedge, pushing out methane hydrate.
As climate change leads to glacier retreat, meltwater might similarly erode hydrates at the edges of other glaciers, Hughes notes. Grounding zone wedges exist across the Arctic, potentially signifying similar risks.
“Perhaps 12,000 to 15,000 years ago, a substantial amount of methane was released. A similar event could occur imminently with ongoing ice sheet retreat,” he warns. “This is concerning as it’s an aspect we’ve yet to fully consider.”
While the study does not estimate the methane released from Melville Bay, Hughes hypothesizes it could be around 130 million tonnes, approximately equivalent to two years’ worth of fossil fuel emissions. However, he notes this methane might have released over a century rather than in a short timeframe, characterizing it as a singular release event.
Furthermore, methane is water-soluble, and depending on saturation levels, not all of it may transition into the atmosphere.
The Antarctic ice sheet likely harbors even more methane hydrate compared to Greenland. Overall, it is estimated that between 100 billion and 760 billion tons of methane exist in subglacial and ocean hydrates across polar regions. A fraction of this could match the 48.7 million tonnes of methane currently released annually from the Arctic and boreal zones, potentially accelerating global warming.
Methane is already seeping from beneath the Greenland ice sheet. A recent study published this month estimates that snowmelt flowing through western Greenland emits around 715 tonnes of methane each year. Though some may stem from hydrates, it’s more likely derived from ancient plant matter converted to methane by bacteria thriving under the ice, led in research by Jade Hutton from the UK Centre for Ecology and Hydrology. This trend may intensify in the future.
“As melting accelerates, it may access regions of the subglacial system harboring well-preserved organic carbon that can be converted to methane,” she predicts. “This could lead to sizable releases in the future.”
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Source: www.newscientist.com
