Survey Finds Trash In The Remotest Ocean Floors

Plastic, fishing gear and 18th-century steamship coal were among the most common finds.
Pham CK et al. doi:10.1371/journal.pone.0095839

We hope you liked the Okeanos Explorer livestream as much as we have. We saw shiny things and creepy things, passive things and aggressive things. We’ve also occasionally seen trash, such as a kitchen glove. For the Okeanos mission, which focused on recording marine life, those were incidental finds. But one recent deep-sea mission sought trash.

The European Union-funded Hotspot Ecosystem Research and Man’s Impact on European Seas (HERMIONE) project reviewed data from previous surveys of 32 locations on the floor of the Atlantic Ocean, Arctic Ocean and Mediterranean Sea. The HERMIONE scientists, a team including marine and geology researchers from several European countries, wanted to see how extensive underwater trash is. Unlike with trash on beaches or floating on the water, data on seafloor litter are harder to come by because underwater missions are expensive and difficult to perform. So this is a rare, comprehensive look at how humans have affected even areas of the ocean that humans have never previously seen. “We were shocked to find that our rubbish has got there before us,” one of the HERMIONE researchers, Kerry Howell of Plymouth University in the U.K., said in a statement.

Howell and her colleagues found all of their study locations had some trash. The most litter-filled locations had more than 20 pieces of trash per hectare (about 2.5 acres). The cleanest places were along continental shelves and had just one or two items per hectare. Plastic was the most common litter material the HERMIONE researchers found. Scientists worry about plastic in the ocean because it can release chemicals into the water that are toxic to marine creatures. The HERMIONE researchers also saw a lot of abandoned fishing gear. These stray lines and nets can catch and kill sea life even though their human owners are no longer using them. The researchers even saw clinker, the burnt remnants of the coal that 18th-century steamships used to burn. Steamship crews regularly dumped clinker overboard. It’s hung out on the ocean floor since.

The remotest location where HERMIONE found litter was on the Mid-Atlantic Ridge, 2,000 kilometers (1,242 miles) away from land. The deepest litter HERMIONE found sat 4,500 meters (2.7 miles) below the surface of the sea.

The HERMIONE team published its findings today in the journal PLOS ONE.