Norwegian Trees Still Bear Evidence of a World War II German Battleship

A chemical fog used to camouflage the ship impacted the trees, limiting ring development

The Nazis regularly used chemical fog to hide its Tirpitz battleship in the Norwegian fjords during World War II. Imperial War Museum/Wikimedia Commons

Germany's World War II battleship the Tirpitz, was among the largest in Hitler’s navy. Commissioned in 1941, the ship spent a large part of the war stationed along the Norwegian coast to prevent an invasion from the Allies.

To hide from possible attacks, the Tirpitz would linger in Norway’s fjords, moving from one fjord to another. The Nazis also released a chemical fog of chlorosulphuric acid for camouflage.

Now, as Jonathan Amos reports for BBC News, scientists have found evidence of this artificial smoke still lingering in the trunks of Norwegian trees.

According to new research, smoke damage caused a period of stunted growth in pine and birch trees at Kåfjord, located in the northern tip of Norway. The team, led by Claudia Hartl, a dendrochronologist at the Johannes Gutenberg University in Mainz, Germany, ​recently presented their work at the European Geosciences Union (EGU) General Assembly in Vienna, Austria.

As Amos reports, Hartl had been examining wood cores to draw a more complete picture of past climate in the region when she noticed that some trees completely lacked rings dating to 1945.

“I thought, ‘Hmm, it’s 1945, that’s strange. It’s the end of the second World War,’” Hartl tells Amos.

Scientists can tell a lot about climate from tree rings. According to the Center for Science Education, a light ring is added each year to a tree’s trunk as it grows quickly in the warmer seasons, while a darker, thinner ring is added during the colder seasons when growth is slow.

But absent growth rings in trees are rare. According to one 2013 analysis of more than 2,000 tree-ring records across the Northern Hemisphere, scientists found that widespread absent rings have only occurred in the southwestern United States in connection to severe drought.

Other options that might stunt tree development are severe cold and even insect infestation, but neither of those theories could explain the total lack of rings in Hartl’s samples. As Hartl tells Amos: “You usually don’t find missing rings in this region.”

Then a colleague suggested the lack of growth in the trees could be related to the Tirpitz. In 1944, before its demise late that year, the Tirpitz was anchored at Kåfjord, where attacks led to the use of chemical fogs.

“These smokescreens caused severe damage to the trees surrounding the Kåfjord,” the researchers write in their abstract.

According to their research, one tree sampled saw no new growth for nine years after 1945. While it later recovered, it took 30 years for it to grow at the same level as before the damage. In other samples, rings were visible but very thin, Amos reports. There was less damage to the trees the farther away they were from Kåfjord. And at about 2.5 miles, trees showed no evidence of damage.

"I think it's really interesting that the effects of one engagement are still evident in the forests of northern Norway more than 70 years later,” Hartl tells Amos.

Hartl believes there might be other places in Europe that show similar patterns of tree damage that can be explained by this artificial smoke, since such chemical screens were not limited to the study area.

As Hartl tells Amos, it’s well known that the Tirpitz had an impact on the region. In fact, in 2017, the Tirpitz museum opened near Kåfjord to showcase the history of a bunker by the same name that was never completed, The Guardian reported last year.

But until now, the environmental impact of the ship has gone undetected.

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