Warming oceans could thaw trapped ‘fire-ice’

Past warming periods may have released trapped methane—a potent greenhouse gas.
Waves on the ocean.
Methane accounts for roughly 16 percent of global greenhouse gas emissions and warmer ocean temperatures could thaw some of the gas trapped beneath the ocean. Deposit Photos

While the name “fire-ice” may sound like an oxymoron, natural gas is very real. Fire-ice or methane hydrate is a natural gas that is frozen solid deep underneath the ocean floor. There is evidence that is previously thawed during periods of warming and released the potent greenhouse gas called methane, according to a study published December 6 in the journal Nature Geoscience. Increasing ocean temperatures from further human-caused climate change could potentially melt more fire-ice, releasing more polluting methane. 

[Related: How AI could help scientists spot ‘ultra-emission’ methane plumes faster—from space.]

Why is methane a problem?

According to the Environmental Protection Agency, methane accounts for roughly 16 percent of global greenhouse gas emissions. It is the second most abundant anthropogenic greenhouse gas after carbon dioxide. It is 25 times more effective than carbon dioxide at keeping heat locked in the atmosphere. However, it has a much shorter half-life than carbon dioxide and generally lingers in the air for less than a decade. 

Agriculture is one of the primary methane polluters, but methane can come from anywhere food or plants decompose without oxygen, like marshes, landfills, and fossil fuels. In 2021, methane emissions was added to a list of climate change priorities to tackle in the next decade by the Intergovernmental Panel on Climate Change. The methane from fire-ice is also believed to have played a role in past climate changes and methane was linked to current ocean warming in the southern hemisphere in 2020

Searching the pockmarks

In the new study, an international team of scientists used advanced 3D seismic imaging techniques to study a portion of fire-ice located off the coast of Mauritania in northwestern Africa. According to the Department of Energy, gas hydrates like these were once believed to be rare, but are now thought to exist in vast volumes and to include 250,000 to 700,000 trillion cubic feet of methane.

[Related: Satellites traced super methane plumes to Turkmenistan’s gas fields.]

The analysis found a specific instance where dislodged methane traveled over 25 miles from the deeper parts of the continental slope up to the edge of the underwater shelf. This possibly occurred when the portion of fire-ice separated during warming periods over the past 2.6 million years, when the frozen gas began to thaw. The methane was potentially released through a field of underwater depressions called pockmarks during past warm periods on Earth. 

“Our work shows they [pockmarks] formed because methane released from hydrate, from the deepest parts of the continental slope vented into the ocean,” study co-author and Newcastle University petroleum geologist Richard Davies said in a statement. “Scientists had previously thought this hydrate was not vulnerable to climatic warming, but we have shown that some of it is.”

Researchers have previously analyzed how changes in bottom water temperature near continental margins may affect the release of methane from hydrates. According to the team, these earlier studies primarily focused on a small portion of global methane hydrates in shallower areas. The new study looks at the release of methane from the base of an area called the hydrate stability zone. This region is if the ocean is roughly 1,476 to 2,296 feet deep. The study found that the methane released from the hydrate stability zone traveled a long distance towards land.

“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,” study co-author and geophysicist at the GEOMAR research institute in Germany Christian Berndt said in a statement. “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.”

The team from this study plans to look for more evidence of methane vents along the margins of the ocean floor. It is planning an expedition to drill further into the ocean’s pockmarks and to search for evidence of past climatic warming events in the geologic record. This kind of data  could help scientists better predict where massive methane seeps are most likely to occur as the effects of human-caused climate change continue to warm the Earth.