Much of Nord Stream's gas remained in the sea

A significant portion of the methane released into the southern Baltic Sea from the Nord Stream gas pipeline has remained in the water, according to measurements taken by researchers at the University of Gothenburg.

In late September 2022, an explosion occurred in the Nord Stream gas pipeline on the floor of the Baltic Sea, east of Bornholm, resulting in one of the largest unnatural methane gas emissions recorded. The released methane formed large bubbles on the water's surface, leading to elevated atmospheric methane levels.

Swift Response

However, much of the methane did not reach the surface and instead dissolved in the water. This finding is based on a scientific study published in Scientific Reports.

“Fortunately, we managed to organize an expedition to the leak area within a week. Based on our measurements, we estimate that between 10,000 and 50,000 tonnes of methane remained dissolved in the sea,” said Katarina Abrahamsson, a professor of marine chemistry at the University of Gothenburg.

The methane spread over vast areas and dissolved in the water, where some of it was processed by bacteria. Methane is also naturally present in the water, formed during the decomposition of organic material in the bottom sediments.

Isotopic Differentiation

“Our study was able to distinguish the methane from the Nord Stream leak from the naturally occurring methane in the water due to the different isotopic composition of the gas pipeline methane compared to that from bottom sediments. This distinction is a strength of our study,” added Abrahamsson.

The sea water typically forms layers due to temperature and salinity differences. Despite the rapid and substantial methane leak from the gas pipeline, the researchers did not observe significant mixing in the water masses. The usual stratification at the end of September remained stable, leading to varying methane levels in the water. Researchers believe that the methane was diluted into a larger body of water later in the autumn as temperatures dropped and water mixing occurred.

Biological Impact Uncertain

It is still too early to determine the impact of the increased methane levels on biological life in the southern Baltic Sea.

“The expedition included researchers who collected plankton samples in the affected area, but the analysis of these samples is not yet complete,” Abrahamsson noted.

Three months after the initial expedition, a follow-up visit was conducted, and new measurements were taken. Preliminary results indicate that bacterial activity has been high over the three months. However, the impact on phytoplankton and zooplankton remains unknown.