During World War II, thousands of battered ships and aircraft sank to the bottom of the world’s oceans. Over time, many of the forgotten wrecks have become artificial reefs that provide shelter for fish and other aquatic wildlife or intriguing sites for scuba divers. But new research suggests the sunken vessels could be doing more harm than good.
Scientists say the V-1302 John Mahn—a German naval ship the British Royal Air Force bombed and sank in February 1942—is leaking toxic chemicals into the North Sea. The team shared the results of their analysis this week in the journal Frontiers in Marine Science.
“Although we don’t see these old shipwrecks, and many of us don’t know where they are, they can still be polluting our marine ecosystem,” says study co-author Josefien Van Landuyt, an ecologist at Ghent University, in a statement.
The vessel, a fishing trawler turned Nazi patrol boat, has been resting below the surface of the Belgian North Sea for the last 80 years. During that time, scientists believe the ship has been polluting the surrounding waters with nickel, copper, arsenic, explosives and chemicals found in fossil fuels known as polycyclic aromatic hydrocarbons, or PAHs. Researchers found the toxic substances in samples taken from the boat’s hull and the nearby ocean floor. The presence of PAHs, in particular, is changing the makeup of the marine ecosystem around the ship.
For now, scientists say the wreck is contributing relatively small amounts of pollution. But it’s just one of many vessels at the bottom of the ocean—and others may be spewing chemicals in higher quantities.
“We only investigated one ship, at one depth, in one location,” says Van Landuyt. “To get a better overview of the total impact of shipwrecks on our North Sea, a large number of shipwrecks in various locations would have to be sampled.”
The new study builds on past research that estimates shipwrecks sunk during World War I and World War II may contain between 2.5 million and 20.4 million metric tons of petroleum products. Fossil fuels aside, as Madison Goldberg writes for Smithsonian magazine, ships are also stocked with materials like paints, cleaners, solvents, batteries, fire extinguishers, ammonia, refrigerants, fishing nets and other equipment.
“None of these are things you want at the bottom of the ocean,” she writes.
The V-1302 John Mahn testing is part of a broader effort to help authorities determine whether wartime vessels will need to be removed from the North Sea. Researchers with the North Sea Wrecks project expect to make a recommendation later this year, reports NewScientist’s Madeleine Cuff.
Researchers don’t know for sure what each vessel was carrying when it sank. But if they held items like “anti-fouling paint or electronics or coal PAHs, they are going to last a long time,” Andrew Turner, an environmental scientist at the University of Plymouth who was not involved in the study, tells NewScientist. “The PAHs at the bottom of the sea will take decades to degrade.”