Methane shock: Nord Stream leak disrupts Baltic's marine sanctuaries

This ecological disaster occurred in September 2022 when three out of four pipelines transporting natural gas from Russia to Germany across the Baltic Sea floor were severely damaged. An underwater explosion ruptured the NS1 and NS2 pipelines near the island of Bornholm in Denmark, causing gas to rise to the sea's surface. The perpetrator remains unknown, but the event has been linked to the effects of Russia's military actions in Ukraine. The explosions took place at a depth of approximately 80 metres under the Baltic surface.

Initially, it was assumed that methane leaked from the damaged pipes and rose into the atmosphere near the Danish island of Bornholm, where the leaks occurred. However, new research indicates that methane spread across large areas of the southern Baltic, up to the Gulf of Gdańsk.

Three new scientific articles appeared in journals Nature and Nature Communications. According to researchers, the methane leak in 2022 from the Nord Stream pipelines released approximately 488,000-535,000 metric tonnes of methane. Most gas entered the atmosphere immediately after reaching the sea's surface. The Voice of the Ocean Foundation quickly responded by sending an underwater drone, known as a glider, to the region just outside the leak exclusion zone. Monitoring continued for three months after the explosion, analyzing the extent of dissolved methane in surrounding waters.

Although most gas reached the atmosphere, a significant portion was absorbed by seawater. In the initial phase after the explosion, the level of dissolved methane in water was sometimes a thousand times higher than standard. Broadly speaking, 14 per cent of the Baltic Sea recorded methane concentrations at least five times higher than natural average values.

The methane leak from the Nord Stream pipeline potentially impacted the protected areas of the Baltic Sea. Scientists noted that ocean currents directed dissolved methane to 23 protected areas. According to researchers, ocean currents carried methane there.

Numerical modelling showed that out of 188 marine protected areas (MPA) in the Baltic, eight were exposed to methane concentrations 100 times higher than normal, and another ten and five such areas were exposed to at least tenfold and twofold increased methane concentrations. However, it should be noted that the long-term impact of increased methane concentrations on marine ecosystems in these protected areas is not yet clear. This is because an event of this scale has never been observed before. According to scientists, further research is necessary to assess the long-term effects of the methane leak on the protected areas of the Baltic Sea.

Martin Mohrmann, a researcher with the Voice of the Ocean Foundation, explained that while low levels of methane pose no threat, the potential long-term effects of high concentrations remain uncertain.

One thing scientists consider particular is the need to reassess the safety of submarine pipelines, especially in increasingly unpredictable times. According to Mohrmann, reassessing the risk for such structures as the Nord Stream pipelines is essential. Risk analyses conducted in 2009 assumed one event every 20,000 years, as well as negligible dissolution of natural gas in water, which now seems doubtful.