A major methane gas leak is flowing from unusual depths of the Baltic Sea, Sweden research expedition finds.

In a recent expedition, researchers at Stockholm University and Linne University detected methane bubbles rising up 370 metres (1,200 feet) from the seabed, a stark contrast to the expected 150-200 metres.

The gas bubbles were found in a 20-square-kilometre (77-square-miles) area off of Sweden’s southeastern coast.

“We know that methane gas can bubble up from shallow seabeds near the Baltic Sea coast, but I’ve never seen such intense bubbles before – and definitely not from such a deep area,” said researcher Christian Stranne, member of the research project, in a statement from Stockholm University.

Stranne explained the oxygen-free conditions in the deep waters of the Baltic Sea could be causing the bubbles to remain more intact, making them rise to the surface more efficiently.

Similar methane leaks could be present in other parts of the Baltic Sea, he said, and the researchers will be carrying out further analysis to understand the cause of high levels of methane release in the area.

“Knowledge about the factors that govern how much methane is produced in these deeper areas and where the methane goes is lacking,” said project leader Marcelo Ketzer, professor of environmental science at Linne University.

Last year, ruptures in the Nord Stream pipeline under the Baltic Sea caused what is likely to be the biggest single release of methane ever recorded, according to the United Nations Environment Programme (UNEP). Methane traps 80 times more heat than carbon dioxide.

Pipelines under the Baltic Sea were carrying natural gas from Russia to Germany when underwater explosions last September caused severe damage.

Accusations of sabotage over the attack have been levelled between the United States and Russia, but investigations have not found conclusive evidence of who was responsible.

In October 2022, the Danish Energy Agency reported the ruptured pipelines had stopped releasing methane.