Nord Stream explosions stirred up tonnes of old mustard gas from the seabed
Sudden seismograph readings and bubbles on the sea surface near Bornholm on September 26 last year indicated that something quite crazy had happened at the bottom of the sea.
Researchers are only now slowly forming a picture of how crazy it truly was.
Danish, Polish, and German researchers revealed a new chapter of the story of the Nord Stream explosions.
Analyses of the area and 3D simulations of current and wind conditions paint a picture of a major resuspension of sediment in one of the most polluted marine areas in Denmark.
A total of 250,000 tonnes of sediment have been stirred up and spread over 11 cubic kilometres of water and 1,200 square kilometres of seabed area—equivalent to twice the size of the area of Bornholm.
The explosions took place 20 kilometres from a well-known dumpsite for, among other things, chemical warfare agents from the Second World War, and the researchers have confirmed the presence of mustard gases in 39 locations. In total, it is estimated that 34.6 tonnes of chemical warfare agents have been stirred up by the explosion.
The researchers have also found the spread of everything from lead over mercury to TBT, which is a strong endocrine disruptor.
In 1947, 11,000 tonnes of chemical warfare agents were dumped east of Bornholm, and the explosions took place to the north and south of the dumpsite.
The sabotage of Nord Stream led to the spread of contaminated sediment over two areas (marked in red), which together make up twice the size of the area of Bornholm:
The problems with contaminants are particularly concentrated around the Bornholm Deep, which is normally a very calm area with very low vertical mixing of water.
Oxygen levels are also low, and the surface of the seabed is covered by a fluffy layer of mud and clay minerals that bind the constantly accumulating material and store it in the sediment.
The Bornholm Deep is a spawning and nursery ground for a very large part of the Baltic Sea’s cod population.
The explosion in September happened at the end of the cod spawning season (March to September), and the researchers estimate that contaminated sediment could affect eggs and juvenile fish for up to a month after the explosion.
This puts the cod stock under additional stress, reads one of the conclusions in the report.
Critically endangered harbour porpoise at risk
Marine mammals in the area are also believed to be strongly affected by the explosions, as the shockwave could both kill the animals and damage their hearing.
This is particularly the case with gray seals, harbour seals, and harbour porpoises, the latter being a critically endangered species in the Baltic Sea.
The typical injuries to the harbour porpoises are bleeding in the ears and loss of their echolocation abilities. The animals that have stayed at the surface have fared significantly better than those at the bottom of the sea.
Calculations show that marine mammals up to 20 kilometres from the explosions have suffered injuries if they have been at a depth of 70 metres.
Animals at the surface have managed to avoid injuries if they have been more than four kilometres away.
In addition to the spread of contaminated sediment, more than 115,000 tonnes of methane seeped out of the ruptured gas pipes over the course of six days and led to emissions equivalent to approximately 15 million tonnes of CO2.
That is a third of Denmark’s total annual CO2 emissions.