Surveys off the coast of Europe revealed all kinds of human trash, including plastic bags (upper left and lower right), beer cans (lower left) and glass bottles (upper right). Photo: Pham et al.
Our garbage is polluting the remotest, deepest ocean
1st July 2014
Even creatures at the bottom of the ocean aren't sheltered from the detritus of human civilization, writes Sarah Zielinski. Everywhere they have looked, scientists have found plastic, glass and other trash littering the seafloor and collecting in canyons.
Not one site was free of human garbage. It was found in the shallowest waters as well as the deepest.
Underwater surveys conducted at dozens of sites in the northeast Atlantic and Acrtic oceans and the Mediterranean Sea have found fishing gear, plastic, metal, glass and other bits of garbage in shallow and deep waters both near and far from shore.
The research, led by Christopher Pham of the University of the Azores in Portugal, was published in PLOS ONE.
Similar studies have documented trash lining the seafloor in other areas, such as Monterey Canyon off California and the more than 7,000-meter-deep Ryukyu trench off the coast of Japan [PDF]. Our trash is everywhere.
Out of sight, out of mind
Around 14 billion pounds of litter makes its way into the world's oceans every year. Some is created when fishing gear is lost. More comes when our trash washes off streets and down through waterways to the sea.
Whole containers of goods may be swept overboard from the numerous ships plying the waves. And plenty of trash was deliberately dumped from barges and ships - a practice only recently banned by international convention.
The trash that floats on top of the ocean - often in great garbage patches at the center of gyres - or that washes onto beaches is most visible and gets the most attention. But plenty of it ends up on the seafloor. It's just harder to see.
"The large quantities of litter reaching the deep ocean floor is a major issue worldwide, yet little is known about its sources, patterns of distribution, abundance and, particularly, impacts on the habitats and associated fauna", Pham and colleagues write.
Not one site was free of human garbage
Pham's team collected data from surveys at 32 underwater sites in the northeast Atlantic and Arctic oceans and the Mediterranean Sea that took place between 1999 and 2011. These surveys either trawled the seafloor or sent down still and/or video cameras to image what was on the ocean bottom.
The surveyed sites were located near as well as thousands of kilometers from shore, at depths of 35 to 4,500 meters, and were located on continental shelves and slopes, ocean ridges, banks, mounds and seamounts and within submarine canyons and deep basins.
Not one site was free of human garbage. The surveys turned up trash along the mid-Atlantic ridge, 2,000 kilometers from shore. It was found in the shallowest waters as well as the deepest.
Top of the list - plastic bags
"Such records were not surprising", Pham's team noted in their paper, "as litter is known to be present in all seas and oceans of the planet, as remote as the Southern Ocean and at depths as deep as 7,216 m in the Ryuku trench, south of Japan."
The most common items were the ubiquitous plastic bags now banned in some cities. There were also glass bottles, fishing lines and nets, wood, cardboard, bits of clothing, pottery and a material called clinker - the residue of burnt coal.
It was common in the late 18th to 20th centuries for steam ships to dump this waste material overboard, so most of this type of trash is more than 100 years old.
The abundance of plastic might be a surprise for some as plastic floats. But about 70% of it eventually sinks to the seafloor, the researchers note.
Abandoned, derelict fishing lines and nets were most often found in areas such as seamounts and banks that host dense communities of fish and shellfish. Those are the regions, of course, where fishing vessels are most likely to ply their trade.
Is there any pristine place left on Earth?
Scientists are still figuring out the global patterns of distribution of all this garbage. But they do know quite a lot about its effects on marine life.
Some organisms eat the trash, thinking its food. Others-especially turtles, marine mammals and birds-get entangled in it, and sometimes die. Fish get caught up in drifting nets, in what's known as 'ghost fishing'.
And chemicals such as dioxins get consumed by small organisms and concentrated in organisms further up the food web, where these poisons can reach lethal levels.
This has to make us wonder: Is there any pristine place left on Earth?
Sarah Zielinski is an award-winning science writer and editor. She is a contributing writer in science for Smithsonian.com and blogs at Wild Things, which appears on Science News.
This article was originally published on Smithsonian magazine.
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