When it set sail on its maiden voyage in 1912, no one could have predicted what the opulent RMS Titanic would look like now – a rusting hulk at the bottom of the Atlantic Ocean.
But at least something remains of the ship, more than a century after its ill-fated transatlantic journey
However, scientists believe that in a few decades there may be nothing left of the ship at all, thanks to a species of bacteria which is slowly eating away its iron hull.
At the time of that initial discovery the ship was remarkably preserved. It is 3.8km below the surface, and the lack of light and the intense pressures make the area inhospitable to most life, slowing corrosion. Fast-forward 30 years, though, and the hull is rusting away, thanks to metal-munching bacteria. Some researchers now give the shipwreck just another 14 years before it is gone forever.
So what do we know about the microbe that is responsible?
The story started in 1991 when scientists from Dalhousie University in Halifax, Nova Scotia, Canada collected samples of icicle-like formations of rust – “rusticles” – hanging from the ship. They took them back to the lab and saw that they were teeming with life.
The bacteria can survive in conditions that are completely inhospitable to most lifeforms on Earth: water that is pitch-black and at crushing pressures.
In 2014, a team of scientists from the US Bureau of Ocean Energy Management (BOEM) conducted perhaps the most in-depth study to date into microbial life on shipwrecks. They looked at eight shipwrecks in the northern Gulf of Mexico. The shipwrecks included wooden-hulled sailing ships dating to the 19th Century, one wooden-hulled sailing ship possibly from as early as the 17th Century, and three World War Two steel-hulled vessels, one of which was sunk by a German U-boat.
They found that the material the ship was built from was the crucial factor that determined the type of microbe that was attracted to the wreck. Wooden ships were teeming with bacteria that attack and feed on the cellulose, hemicellulose, or lignin found in wood. Steel ships, on the other hand, were occupied mostly by iron-loving bacteria.
Strangely, although the bacteria were essentially feeding on the ship, they actually served to protect them from corrosion.
“In essence, what happens is that any vessel that sinks, be it a wooden 19th-Century ship or a steel-hulled ship from World War Two, once it hits the floor it becomes available to microbes that rush to cover every surface,” says marine archaeologist Melanie Damour at BOEM in New Orleans, Louisiana, one of the expedition’s lead scientists.
“At first the ship will begin to corrode as it is in contact with seawater, but as microbes begin to colonise the wreck they begin to form a biofilm, which forms a protective layer between the ship and the seawater,” says Damour.
This means that any kind of mechanical impact, such as an anchor dragging across the wreck, will break through that protective crust and open the bare metal to the seawater again, speeding up corrosion.
It is not just mechanical impact that can speed up the corrosion. The 2010 Deepwater Horizon disaster spewed millions of gallons of oil into the Gulf of Mexico, and much of it entered the deep ocean. In laboratory experiments, the team has found that exposure to oil can speed up the corrosion of shipwreck material. This suggests that oil from the Deepwater Horizon spill may be accelerating the corrosion of shipwrecks on the seafloor, but the team have not yet been able to find out if this is really happening.
The finding is alarming. More than 2,000 sunken ships lie on the Gulf’s seafloor, including everything from 16th-Century Spanish vessels to the ruins of a World War Two U-boat. These shipwrecks are important historical monuments, which provide unique insight into the past. They also provide a home for deep-sea life.
But eventually, all the shipwrecks – including Titanic out in the Atlantic – will be eaten away entirely, whether through metal-munching bacteria or seawater corrosion. The iron in the 47,000-tonne vessel will end up in the ocean. Eventually, some of it will be incorporated in the bodies of marine animals and plants. The Titanic will have been recycled.