The Arctic Seafloor Is Degrading and Could Be a Climate Time Bomb

Up to a trillion tons of methane, a powerful greenhouse gas, may be locked away in the decaying ocean floor of a vast Arctic continental shelf.
Up to a trillion tons of methane, a powerful greenhouse gas, may be locked away in the decaying ocean floor of a vast Arctic continental shelf.
Ice in the East Siberian Sea. Image: NOAA

Trouble is bubbling up from the depths of a vast region of Arctic seafloor that is little explored, but nevertheless could have major repercussions for the global climate, reports a new study. 

The East Siberian Arctic Shelf (ESAS) extends for some 770,000 square miles—an area bigger than Mexico—off the coast of Siberia, making it the widest and shallowest continental shelf in the world’s ocean. The shelf contains enormous reserves of methane, a powerful greenhouse gas, that have been locked up for thousands of years under an impermeable layer of permafrost, which is a type of frozen sediment. 


However, expeditions to the shelf led by Evgeny Chuvilin, a geoscientist at Skolkovo Institute of Science and Technology (Skoltech)—a private university founded in partnership with MIT—in Moscow, Russia, “demonstrate progressive degradation of subsea permafrost which controls the scales of [methane] release from the sediment into the water-atmospheric system,” according to a recent study published in the journal Marine and Petroleum Geology. While this degradation is primarily occurring due to natural pressures, human-driven climate change may also be playing a role.

The new research confirms previous studies that raised alarms about the potentially catastrophic release of methane from icy gas-rich solids known as hydrates, while also revealing new insights about the shelf with much-needed in-situ measurements from the field.  

“The East Siberian shelf remains a poorly studied area, especially regarding the thermal characteristics of bottom sediments and the conditions for the existence of subsea permafrost and gas hydrate accumulations,” said Chuvilin in an email.

“The degradation of underwater permafrost on the Arctic shelf may result in large amounts of greenhouse gasses, predominantly methane, escaping into the atmosphere,” he added. “It is unknown precisely how many methane reserves exist in subsea permafrost and sub-permafrost horizons on the Arctic shelf. Still, current estimates suggest that there can be up to a trillion tons of methane on the East Siberian shelf alone.”


For comparison, an estimated 570 million tons of methane are released into the atmosphere globally each year, a number that is dwarfed by the reserves locked up in the ESAS. Scientists are concerned both by the gargantuan volume of gas reserves and the shallow depth of the ocean over much of the shelf, which makes it easier for greenhouse gasses to bubble up to the surface and into the atmosphere, compared to deeper waters that can absorb these emissions.

That’s why researchers are racing to better understand the murky layers within the shelves and produce more accurate projections of the volume of gas that might be released from them in the coming years.

To that end, Chuvilin and his colleagues embarked on Arctic sea expeditions in 2019 and 2020 that extracted cores from the ocean floor.

“Our task was to study the composition and various physical characteristics of bottom sediments on the Arctic shelf, including their temperature, thermophysical properties, and freezing and thawing points,” Chuvilin said. “We took samples of the bottom sediment core during the Arctic expeditions to do this. The samples were taken aboard very quickly, within minutes, to immediately measure temperature, thermal conductivity, and heat capacity,” which were analyzed with a handheld device called a KD2 Pro.


“In addition, we took samples of bottom sediments for detailed lab studies of their characteristics, such as dispersion, humidity, salinity, and mineral composition,” he noted. “Our lab research also identified the sediments’ freezing point using an in-house technique that we described in the paper.”

The results revealed both anomalously cold and hot bottom sediments in different parts of the shelf. At depths of about 330 meters along the continental slope of the Laptev Sea, sediments reached −1.8°C, which is colder than expected and could be the result of interior seabed processes or frigid water cascading along the shelf. 

However, at shallower depths, the team saw abnormally high temperatures reaching 2°C, which is warm enough to degrade permafrost. The researchers think these areas might be warmed in part by Siberian river systems that flow into the sea. While subsea permafrost decay is primarily caused by natural pressures, including seismic and tectonic activity, these warm river flows are exacerbated by human-driven climate change.

“The role of human-caused climate change has yet to be assessed, but apparently, it manifests itself as warming of sea waters and Siberian river flows,” Chuvilin said. “The available data shows that the flows of Siberian rivers strongly affect the temperature of bottom sediments and subsea permafrost on the shallow Arctic shelf.”

Human-driven climate change, which is caused by greenhouse gas emissions from our consumption of fossil fuels, is particularly devastating to polar regions. The Arctic is warming at least twice as fast as any other region on Earth, which has resulted in many severe consequences for Siberia and its huge swaths of permafrost.


In recent years, the region has suffered record-breaking temperatures and severe wildfires as a result of climate change. Chuvilin and his colleagues are also studying Siberia’s bizarre natural gas explosions linked to permafrost thaw, which have left massive craters in the landscape. The effects of global warming have, of course, been much more noticeable on land, but the new research suggests that more attention should be paid to the potential time-bomb of methane emissions locked away in the Arctic shelf. 

“We plan to continue studying the thermal state of bottom sediments on the Arctic shelf and assess the mode of occurrence of subsea permafrost and gas hydrates,” Chuvilin said, noting that these efforts will include “mathematical and experimental modeling of the evolution and degradation of permafrost and gas hydrates on the Arctic shelf.” 

“Aside from the thermal characteristics, this comprehensive study will involve geophysical research to glean more knowledge about subsea permafrost’s top and bottom, probing deeper horizons of bottom sediments using drilling, and monitoring intensive methane emission areas on the Arctic shelf,” he concluded.