Thousands of tons of methane may have dissolved in the Baltic Sea water, but the consequences for marine life are unclear

Researchers warn of possible shifts in marine life and carbon cycles after the pipeline explosion

A piece of Nord Stream pipe on display in Kotka, Finland. Photo: Wikimedia Commons, CC BY-SA 4.0

A new study has shed light on the fate of methane released in the September 2022 explosions that damaged the Nord Stream pipelines in the Baltic Sea. Although a significant amount of methane escaped, the investigation after the explosions probably dissolved 10,000 to 50,000 tons into the surrounding water.

While the immediate environmental impacts remain unclear, the study highlights the potential impacts on the marine ecosystem. The environmental consequences of excess methane – a potent greenhouse gas – include local impacts on the carbon budget in water and changes in the composition of microbial organisms, according to the study published in the journal Scientific reports noted.

“Previous studies have mainly focused on smaller leak locations. The scale of the Nord Stream incident is among the largest known,” the researchers wrote in their article.

Read more: Nord Stream is leaking: where does Europe get its gas from now?

Nord Stream comprises a network of offshore pipelines (Nord Stream 1 and 2) that supply natural gas to Northern Europe. They run across the seabed of the Baltic Sea, from Russia to northern Germany.

The pipelines transport a huge amount of fossil fuels every year – about 20 multiplied by 10 to the 12th power in tons.

However, on September 26, 2022, the Nord Stream 1 and 2 pipelines suddenly began leaking at four locations in the Swedish and Danish economic zones, prompting countries as well as Germany to launch an investigation, suspecting “sabotage.” Sweden and Denmark have now closed the investigation.

Meanwhile, scientists estimated the amount of methane that entered the atmosphere and dissolved in seawater.

The European Space Agency satellite observed the plume at the Danish leak site and estimated that an estimated 79 tons of methane per hour reached the atmosphere through the Nord Stream 2 breach.

Read more: The Nord Stream leak is the largest methane leak ever, but minuscule compared to global emissions of the greenhouse gas: UNEP

The direct transfer of fossil gas to the atmosphere ended after seven days. The rest continued to dissolve in the seawater.

The study authors estimated that if the same amount of methane were to escape from the three major leaks over seven days, about 40,000 tons of the gas would be released into the atmosphere. Another recent study calculated that emissions into the atmosphere were 2,20,000 tonnes.

To investigate the amount of methane dissolved in seawater and its effects, scientists from Sweden and Germany set out on an expedition to the site a week after the explosion. They collected water samples for analysis from up to 10 separate water depths across the entire water column. They also measured the methane concentration in the atmosphere continuously at night.

The methane from fossil gas has a different isotopic composition than the naturally occurring methane in the sea, allowing the team to distinguish between the two.

The team estimated that the total amount of methane in the water was between 10,000 and 55,000 tons, although they acknowledged that their measurements could be inaccurate. However, they added that because sites were not included in the study, their assessment may have underestimated the amount of total dissolved methane.

Read more: UNEP calls Nord Stream methane leak ‘largest ever’; plume over Europe disappears

The high concentration of methane in surface water after the Nord Stream gas leak may promote the growth of methanotrophic bacteria, affecting the microbial food web in the Baltic Sea. This bacteria uses methane as the sole source of carbon and energy.

“The expedition also involved researchers who took plankton samples (plants and animals that drift with the tides and currents of the sea) in the affected area, whose analyzes have not yet been completed”, Katarina Abrahamsson, professor of marine chemistry at the University of Gothenburg, in a statement.

The researchers returned to the site three months after the leak and took new measurements. The team observed high bacterial activity over the three months. The researchers have yet to see how this affects the plankton.

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