According to the survey, plastic and fishing gear are the most common litter items found on seafloors. “Some sites seem authentic garbage dumps”, affirms Professor Miquel Canals. Seafloor litter is a threat to many marine organisms. Marine litter accumulations can be found in submarine canyons.

02/05/2014

Recerca

A new paper published on the journal PLOS ONE alerts that even in the deepest ocean depths you can find bottles, plastic bags, fishing nets and other types of human litter. Experts from the Consolidated Research Group on Marine Geosciences of the University of Barcelona (UB), led by Professor Miquel Canals, participated in the seafloor survey.

Marine litter is a serious environmental problem that affects coastal and oceanic ecosystems all over the planet. Geologists Galderic Lastras and Xavier Tubau (UB) also participated in the survey that describes the presence of litter on Mediterranean, Arctic and Atlantic seafloors —from the continental shelf of Europe to the Mid-Atlantic Ridge— at all depths (from 35 m down to 4500 m).

Plastic, fishing gear, glass, metal, wood and clothing

Plastic and fishing gear are the most common litter items found on seafloors. Glass and metal, wood, paper/cardboard, clothing, pottery, and unidentified materials were also observed.

“Some sites seem authentic garbage dumps”, affirms Miquel Canals, from the Department of Stratigraphy, Paleontology and Marine Geoscience of UB. “In oceans, litter is present everywhere, from the most remote points, like the Arctic or the Southern Ocean, to abyssal plains, at thousands of metres deep”. “The type of litter found on seafloors is diverse: we found solid objects —particularly plastics and cans—, but also microplastics generated due to plastic degradation. A predominance of derelict fishing gear was observed in areas of great fishing activity”, he adds.

The international study involving fifteen organisations across Europe, was led by the University of the Azores, and is a collaboration between the Mapping the Deep Project led by Plymouth University and the European Union-funded HERMIONE and PERSEUS projects, coordinated by the National Oceanography Centre in Southampton and the Hellenic Centre for Marine Research, respectively. The project Dos Mares of the Spanish National R&D Plan, coordinated by Canals, also collaborated in the survey.

When rubbish gets there before humans

Christopher Pham, from the University of the Azores, explains: “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”.

“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”, states Kerry Howell, professor at Plymouth University’s Marine Institute. “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”.

There is not any reliable global map of the oceanic areas most affected by marine litter impact. “Current and marine dynamics distribute litter from initial dumping locations to the ocean’s interior”, affirms Miquel Canals. “Main initial dumping sources —he points out— are coastal urban and industrial areas, beaches, tourism-related activities, and shipping activities. Rivers and wind also play an important role in transporting litter to the coast and into the sea”.

What is the impact on the Catalan coast?

Closed seas, like the Mediterranean, with large urban and industrial areas, probably accumulate more litter than remote oceanic regions. Within the survey, the team of the Consolidated Research Group on Marine Geosciences of UB provided some sea images of the Blanes Canyon, got in 2011 with the remotely operated underwater vehicle Liporus 2000, of the Spanish Oceanographic Institute (IEO), during the oceanographic campaign Promares-Oasis del Mar to study Catalan submarine valleys.

Canals explains that “dense water strong currents happen in the occidental Mediterranean; they preferably circulate throughout marine canyons. Therefore, we think that these areas accumulate more litter than other sites. On the Catalan coast, fishing activity litter can be particularly found on the continental shelf and talus, at 900 m deep; they are particularly accumulated on rock seafloors in submarine canyons, where there are many derelict fishing lines and nets”.

Marine litter: a deep problem in seas and oceans

The survey also reveals post-industrial marine navigation’s footprint. “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”, explains Eva Ramirez-Llodra, researcher from the Spanish Research Council (CSIC). 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.

Million tons of litter are dumped into the sea every year. The study reveals that even in the deepest ocean you can find marine litter. “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”, concludes Professor Kerry Howell.

Miquel Canals remarks: “The most surprising is to confirm once again that human footprint has arrived to the most remote sites of our planet”.

Images: Consolidated Research Group on Marine Geosciences of UB