Thousands of tonnes of methane may have dissolved in Baltic seawater, marine life impacts unclear

A new study has shed light on the fate of methane released from the September 2022 explosions damaging the Nord Stream pipelines in the Baltic sea. While a significant amount of methane escaped, 10,000 to 50,000 tonnes of it likely dissolved in the surrounding water after the blasts, the research suggested.

While the immediate environmental impact remains unclear, the research highlighted potential consequences for the marine ecosystem. The environmental implications of excess methane — a potent greenhouse gas — include local impacts on water carbon budgets and changes to the composition of microbial organisms, the study published in journal Scientific Reports noted.

“Previous studies have primarily focused on smaller leakage sites. The scale of the Nord Stream incident is among the largest known,” the researchers wrote in their paper.

Read more: Nord Stream leaks: Where will Europe get its gas from now?

Nord Stream comprises a network of offshore pipelines (Nord Stream 1 and 2) supplying  natural gas to northern Europe. They run on the sea floor of the Baltic sea from Russia to northern Germany. 

The pipelines transport a massive amount of the fossil fuel annually — roughly 20 multiplied by 10 to the 12th power in tonnes. 

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 both countries and Germany to launch an investigation, suspecting “sabotage.” Sweden and Denmark have since closed the investigation.

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

The European Space Agency satellite observed the plume at the Danish leakage site and estimated that 79 tonnes of methane per hour was estimated to have reached the atmosphere from the Nord Stream 2 breach.

Read more: Nord Stream spill is biggest methane leak ever, but minuscule compared to global release 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 authors of the study assumed that if the same amount of methane escaped from the three major leaks during the seven days, around 40,000 tonnes of the gas was released into the atmosphere. Another recent study calculated that the emission to the atmosphere was 2,20,000 metric tonnes.

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

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

The team estimated that the total amount of methane in the water ranged between 10,000 and 55,000 metric tonnes, although they acknowledged that their measurements could be inaccurate. They did, however, add 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 ‘biggest-ever’; plume over Europe fading

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

“The expedition also included researchers who took plankton samples [plants and animals that float with the sea’s tides and currents] in the affected area, the analyses of which are not yet complete,” Katarina Abrahamsson, professor of marine chemistry at the University of Gothenburg, said in a statement.

The researchers returned to the site three months following the leak and took new measurements.The team observed high bacterial activity during the three months. The researchers are yet to see how this impacts the plankton.