By Roberta Attanasio
We’re all familiar with the global threat of ocean pollution — and the widespread presence of plastic on beaches and in the great garbage patches. However, until very recently, we did not know that marine litter is present in large amounts on the seafloor, in the deepest areas and at very remote locations. Marine litter is defined by the United Nations Environment Programme (UNEP) as ‘‘any persistent, manufactured or processed solid material discarded, disposed of or abandoned in the marine and coastal environment”. Results of a survey published in the scientific journal PLoS ONE on April 30, 2014, reveal the magnitude of the problem.
Researchers gathered data from surveys carried out during research cruises led by various European institutions between 1999 and 2011. A total of 32 sites were surveyed — in the northeastern Atlantic Ocean, Arctic Ocean and Mediterranean Sea — at depths ranging from 35 meters to 4.5 kilometers. The sampling methods used for the survey included imaging technology (still photograph and video) as well as fishing trawls.
The researchers found litter at each site surveyed, with plastic accounting for 41% and discarded fishing gear for 34% of it. In addition, they found glass, metal, wood, clothing, pottery, paper and cardboard, as well as unidentified materials. The most prevalent litter item found on the seafloor was plastic (bottles, bags, etc.), whereas discarded fishing lines and nets were particularly common on underwater mountains, banks, mounds and ocean ridges.
It is commonly believed that most plastic items float at the sea surface — in reality, an estimated 70% of the plastic that reaches the ocean sinks to the seafloor. Indeed, results from the survey show that, for example, litter is present at larger density on the seafloor of the Mediterranean Sea as compared to the litter floating at the surface.
Kerry Howell (Plymouth University’s Marine Institute), one of the researchers involved in the study, said in a press release “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.”