Lawrence LeBlond for redOrbit.com – Your Universe Online
A study released last year confirmed just how far human trash sinks in the ocean, finding detritus as much as 13,000 feet deep off the coast of California. Now, a new study published in the journal PLOS ONE has revealed that even the deepest ocean depths is home to bottles, plastic bags, fishing nets and other types of human litter.
The new study, led by Cristopher Pham of the University of the Azores, focused on the Mediterranean and all the way from the continental shelf of Europe to the Mid-Atlantic Ridge, finding human litter as far as 1,200 miles out to sea. Pham’s research was conducted with the help of colleagues from 15 other institutions around the world.
The study is also a collaboration between the Mapping the Deep Project led by Plymouth University and the European Union-funded HERMIONE Project, coordinated by the National Oceanography Centre in Southampton, UK. The British Geological Survey contributed to the study as well.
Human litter is a major problem in the marine environment as it can be mistaken for food and eaten by many marine animals, such as whales, dolphins and sharks. It can also entangle fish, sea turtles and other marine wildlife – a process known as “ghost fishing,” or ghost netting.
For the study, scientists took nearly 600 samples from across the Atlantic and Arctic Oceans and from the Mediterranean Sea, from depths ranging from 115 feet to more than 14,500 feet. The teams used photos, videos, and trawling techniques to survey or collect litter on the seafloor. The litter was classified into six categories: plastic, fishing gear, metal, glass, clinker, and other.
“We found that plastic was the most common litter item found on the seafloor, while trash associated with fishing activities (discarded fishing lines and nets) was particularly common on seamounts, banks, mounds and ocean ridges. The most dense accumulations of litter were found in deep underwater canyons,” Pham said in a statement.
“This survey has shown that human litter is present in all marine habitats, from beaches to the most remote and deepest parts of the oceans. Most of the deep sea remains unexplored by humans and these are our first visits to many of these sites, but we were shocked to find that our rubbish has got there before us,” added Dr Kerry Howell, Associate Professor at Plymouth University’s Marine Institute.
Each site surveyed contained some form of litter. Plastic accounted for 41 percent of all litter found and fishing gear second at 34 percent. However, the study also found samples of glass, metal, wood, paper/cardboard, clothing, pottery, and other unidentified materials
“An interesting discovery was relating to deposits of clinker on the sea floor – this is the residue of burnt coal that had been dumped by steam ships from the late 18th century onwards. We have known that clinker occurs on the deep-sea bed for some time, but what we found was the accumulation of clinker is closely related with modern shipping routes, indicating that the main shipping corridors have not been altered in the last two centuries,” Dr Eva Ramirez-Llodra, a marine biologist from the HERMIONE Project, said in a statement.
The report not only looks at what human litter can be found in the world’s oceans, but also outlines the path that plastics – in particular – can take, originating from coastal and land sources and being carried along continental shelves and slopes into deeper waters before nestling onto the seafloor.
“Submarine canyons form the main connection between shallow coastal waters and the deep sea. Canyons that are located close to major coastal towns and cities, such as the Lisbon Canyon offshore Portugal, or the Blanes Canyon offshore Barcelona, can funnel litter straight to water depths of 4,500m or more,” noted Dr Veerle Huvenne, Seafloor and Habitat Mapping Team Leader at the National Oceanography Centre.
“This very important research confirms what most of us who work in the deep ocean have noticed for quite some time – that human rubbish has got there before us,” Jonathan Copley, senior lecturer in marine ecology at the University of Southampton, told The Guardian.
“But this paper presents an analysis of the kinds of rubbish, what is common where, and what sort of activities are having the most impact in terms of rubbish reaching the deep ocean in different regions. People are piecing this together on a global scale to appreciate how widespread this problem is potentially,” added Copley, who was not involved in the research.
“The large quantity of litter reaching the deep ocean floor is a major issue worldwide. Our results highlight the extent of the problem and the need for action to prevent increasing accumulation of litter in marine environments,” noted the authors.