(CNN) — Marine scientists have discovered deep sinkholes, one larger than a city block with six-story buildings, and ice-filled hills that have formed “extraordinarily” quickly in a remote part of the ocean floor. Arctic.
Mapping Canada’s Beaufort Sea, using a remotely operated underwater vehicle and ship-mounted sonar, revealed the dramatic changes that researchers say are occurring as a result of thawing submerged permafrost beneath the seafloor.
An autonomous underwater vehicle is recovered following completing a seafloor mapping mission in the Arctic Ocean. The remotely operated vehicle (foreground) is used to conduct visual surveys of the newly mapped seafloor.
The changes the scientists observed occurred between 2010 and 2019, during which four mapping studies were conducted, covering an area of up to 10 square miles (26 square kilometers).
It’s the first time an area of submerged permafrost, a frozen layer of the Earth’s surface, has been examined in this way, and it’s not known how widespread similar changes are elsewhere in the Arctic.
On land, thawing permafrost has caused sweeping changes in the Arctic landscape, including the collapse of the ground, the formation and disappearance of lakes, the appearance of mounds called pingos, and craters formed by explosions of methane gas contained in the permafrost. These extreme characteristics have affected infrastructure such as highways and oil pipelines.
“We know there are big changes happening across the Arctic landscape, but this is the first time we’ve been able to deploy technology to see that changes are happening offshore as well,” said marine geologist Charlie Paull, senior scientist at Monterey Bay. Aquarium Research Institute and one of the lead authors of a study on the phenomenon published Monday in the peer-reviewed scientific journal PNAS.
“Clearly such large changes would have significant implications for any infrastructure that might be placed on the seafloor. Currently, there is little infrastructure in this remote region of the Arctic. However, this may change as continued warming makes the region more accessible,” he added.
‘Unexpected’
About a quarter of the land in the Northern Hemisphere is covered by permafrost, Paull said, including large areas under the sea. This is because at the end of the last ice age, around 12,000 years ago, large areas of permafrost were submerged as glaciers melted and sea levels rose.
In the 10-square-mile (26-square-kilometer) study area, mapped in 2010 and once more in 2019, the researchers found 41 steep-sided holes in the most recent mapping that weren’t there before. The holes were roughly circular or oval and averaged 22 feet (6.7 meters) deep. The biggest change was a depression 95 feet (29 meters) deep, 738 feet (225 meters) long and 312 feet (95 meters) wide, the size of a city block made up of six-story buildings.
Autonomous underwater vehicle mapping detailed the unusually rugged seafloor terrain along the edge of the continental shelf in the Arctic. Sinkholes have developed where permafrost at depth has thawed.
The research team also found “numerous” hills, typically 164 feet (50 meters) in diameter and 33 feet (10 meters) high, that contained ice. They are similar to pingos, ice-filled mounds found on land, according to the study.
Studies of smaller areas of the seafloor were conducted in 2013 and 2017, allowing researchers to understand the changes in greater detail.
Evgeny Chuvilin, a research scientist at Skoltech in Russia who has studied Siberian permafrost, said it was surprising to see changes like these happening in such a short time.
“Permafrost degradation is a slow process. Usually we are talking regarding centimeters per year. This here is more than just degradation, it is also a qualitative change. So I would say yes, it is unexpected to see it,” said Chuvilin, who did not participate in the research.
“Hypotheses have been expressed in the literature regarding the possibility of such processes, but this is the first time they have been observed directly.”
Rapid changes in the Arctic
Huge craters have been discovered in parts of the Russian Arctic that were formed when pockets of methane gas in the ground spontaneously exploded.
However, the Beaufort Sea researchers ruled out a similar origin for the marine sinkholes they discovered. The team found no rocks or soil on the seafloor that had been scattered by such an explosion.
Furthermore, brackish (slightly salty) water near the seafloor suggested that seawater was mixed with groundwater and that the underwater permafrost was not a sealed system where overpressure might build up. They also did not detect significant amounts of methane in the filtered groundwater.
“We have no evidence that rapid changes in this area are associated with explosive events,” Paull said by email.
The role of climate change
Many of the landscape changes seen in terrestrial permafrost have been attributed to warmer temperatures as a result of the climate crisis: the Arctic is warming twice as fast as the global average. However, the authors said the changes they had identified might not be explained by human-caused climate change.
“Since this is the first study of submerged permafrost decomposition, we don’t have long-term data for seafloor temperature in this region. The data we do have shows no warming trend in these waters at 150 meters (nearly 500 meters). feet) deep,” Paull said.
Instead, the holes were likely caused by much older, slower climate changes that are related, he said, to our emergence from the last ice age and appear to have been going on for thousands of years.
“Heat carried by slow-moving groundwater systems is contributing to the breakdown of submerged permafrost, creating large sinkholes in some areas and ice-filled hills called pingos in other areas,” Paull said.
The water-filled cavities had replaced the excess ice that was once contained within the permafrost. When these cavities collapsed, the large sinkholes seen in this study quickly formed, he explained. The pingo-shaped mounds formed where brackish water produced by decomposing permafrost migrated up and froze, blistering the seabed with ice-cored mounds.
While the temperature of groundwater was unknown, if it was 1.8 degrees Fahrenheit (1 degree Celsius) above freezing, it might melt a column of ice for thousands of years, according to the study.
Unlike terrestrial permafrost, which can respond on the scale of years to decades to climate change, underwater permafrost has a much slower response time in terms of climate impacts, said Sue Natali, director of the Arctic program and chief scientist of the climate research center in Massachusetts. “The changes described in this study are responding to events that occurred during the centennial to millennium time period. That said, these changes may still affect the climate if they result in greenhouse gas emissions as underwater permafrost thaws.” “. Natali was not involved in the study.
