The seabed of the North Sea is covered in thousands of ship and aircraft wrecks, warfare agents, and millions of tons of conventional munition such as shells and bombs.

Wrecks contain hazardous substances (such as petroleum and explosives) that may harm the marine environment. Yet, there is a lack of information about the location of the wrecks, and the effect they might have on the environment.

It is estimated that World War I and II shipwrecks around the world collectively contain between 2.5m and 20.4m tons of petroleum products.

 Josefien Van Landuyt, of Ghent University, explained:

“The general public is often quite interested in shipwrecks because of their historical value, but the potential environmental impact of these wrecks is often overlooked.

“While wrecks can function as artificial reefs and have tremendous human story-telling value, we should not forget that they can be dangerous, human-made objects which were unintentionally introduced into a natural environment. Today, new shipwrecks are removed for this exact reason.”

“We wanted to see if old shipwrecks in our part of the sea (Belgium) were still shaping the local microbial communities and if they were still affecting the surrounding sediment. This microbial analysis is unique within the project.”

As part of the North Sea Wrecks project, Van Landuyt and her colleagues investigated how the World War II shipwreck V-1302 John Mahn in the Belgian part of the North Sea is impacting the microbiome and geochemistry in its surrounding seabed. Their findings have been published in Frontiers in Marine Science: 80 years later: Marine sediments still influenced by an old war ship

The V-1302 John Mahn

The V-1302 John Mahn was a German fishing trawler that was requisitioned during World War II to use as a patrol boat. In 1942, during ‘the Channel Dash’, it was attacked by the British Royal Air Force in front of the Belgian coast, where it quickly sank to the bottom of the sea. 

The JOHN MAHN was registered under the fishery identification number BX 221 (BX = Bremerhaven) at 09.03.1932. Before that the number SD 131 [SD = Altona] was given to the ship. Since 28.09.1939 it was part of the 13^th Outpost Boat Flotilla (13. Vorpostenflottille) as Vp 1302. At 12.02.1942 the Vp 1302 was used, together with the Vp 1303, as marking boat during the Operation CERBERUS. The aim of this operation was the breakthrough of the battleships SCHARNHORST, GNEISENAU and PRINZ EUGEN through the English Channel into the North Sea. During this operation the Vp 1302 was attacked by airplanes at 15:53, and after it was hit by 2 aerial bombs sunk, ca. 20 nm northwest of Zeebrügge; 12 crew members died.

German Maritime Museum

To analyze the bio- and geochemistry around the shipwreck, the researchers took steel hull and sediment samples from and around it, at an increasing distance from it and in different directions.

They found varying degrees of concentrations of toxic pollutants depending on the distance from the shipwreck. Most notably, they found heavy metals (such as nickel and copper), polycyclic aromatic hydrocarbons (PAHs; chemicals that occur naturally in coal, crude oil, and gasoline), arsenic, and explosive compounds. 

The highest metal concentrations were found in the sample closest to the ship’s coal bunker. The freshly deposited sediment in the wake of the wreck had a high metal content. The highest PAH concentrations were closest to the ship.

They also found that the ship influenced the microbiome around it. Known PAH degrading microbes like Rhodobacteraceae and Chromatiaceae were found in samples with the highest pollutant content. Moreover, sulfate reducing bacteria (such as Desulfobulbia) were present in the hull samples, likely leading to the corrosion of the steel hull.