Vast amounts of fire-ice – frozen methane trapped under our oceans – is more vulnerable to melting than scientists previously thought possible.
And when fire-ice thaws it releases its potent greenhouse gas into our oceans and, potentially, our atmosphere.
An international team of researchers led by Newcastle University has discovered that, not only is fire-ice in our deep oceans affected by global warming, but the methane it releases as it melts can reach the sea floor and travel significant distances.
Contents:
What is fire-ice?
It exists under the ocean. It’s an ice-like structure you can burn, producing a flame.
Fire-ice is frozen methane gas and water – or methane hydrate. It is stable in sediment in our oceans where water depths are greater than 450–700m.
It thaws when ocean temperatures rise, venting methane into the ocean and, potentially, the atmosphere. This is known as dissociated methane.
Methane in our world
Methane released in our oceans can contribute to ocean acidification. When seawater becomes more acidic the concentration of carbonate ions – important building blocks for shelled marine life and reef-building corals – is reduced. Increased acidification can also impact fish species.
Methane in our atmosphere is 25 times more potent than carbon dioxide (CO2) at trapping heat in the atmosphere.
The gas is also the second most abundant anthropogenic greenhouse gas after CO2. Figures from the United States Environmental Protection Agency show that methane accounts for about 16% of global greenhouse gas emissions.
Seismic discovery
Using advanced three-dimensional seismic imagery, scientists studied the hydrate that dissociated during past climatic warming off the coast of Mauritania in North West Africa.
Although the data had already been extensively examined, they discovered a large field of 23 underwater depressions, known as pockmarks, indicating massive methane venting.
The pockmarks had been missed because they weren’t located where it was thought methane hydrate was vulnerable to thawing.
When the source of the methane was traced, it was discovered to have migrated from the deep ocean – 40kms oceanward of the pockmarks.
Professor Richard Davies, Pro-Vice-Chancellor, Global and Sustainability, is lead author on the paper ‘Long-distance migration and venting of methane from the base of the hydrate stability zone’, published in the journal Nature Geoscience.
He said: ‘I revisited imaging of strata just under the modern seafloor offshore of Mauritania and pretty much stumbled over the pockmarks.
‘Our work shows they formed because methane released from hydrate, from the deepest parts of the continental slope, vented into the ocean.’
Understanding hydrate venting
As methane hydrate occurs immediately below the seabed it is sensitive to changes in bottom water temperature near continental margins – the outer edge of the Earth’s continental crust where it meets the oceanic crust.
Scientists have previously studied both how these temperature changes affect the release of methane and the landward limit of the hydrate stability zone.
Professor Davies said: ‘We used to think that the only part of the methane hydrate that you needed to worry about was located at about 500m water depth.
‘What we hadn’t realised was the methane hydrate located tens of kilometres seaward of that – in the deep water, down at one- or two-kilometre depths – could also be vulnerable.’
Professor Dr Christian Berndt, Head of the Research Unit Marine Geodynamics, GEOMAR, in Kiel, Germany, added: ‘This is an important discovery. So far, research efforts focused on the shallowest parts of the hydrate stability zone, because we thought that only this portion is sensitive to climate variations.
‘The new data clearly show that far larger volumes of methane may be liberated from marine hydrates and we really have to get to the bottom of this to understand better the role of hydrates in the climate system.’
What’s next?
The research will play a key role in helping to predict and address the impact of methane on our changing climate.
The team plans to continue searching for evidence of methane vents along the continental margin and try to predict where massive methane seeps are likely to occur as the planet warms.
A scientific cruise to drill into the pockmarks to see if they can be more closely tied to past climatic warming events is also being planned.
You might also like:
- Read the paper: Richard J. Davies, Jinxiu Yang, Mark T. Ireland, Christian Berndt,Miguel Ángel Morales Maqueda & Mads Huuse. Long-distance migration and venting of methane from the base of the hydrate stability zone Nature Geoscience. doi:10.1038/s41561-023-01333
- find out more in our press release
- watch the video
- learn more about Professor Richard Davies
