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Planet Earth

Inventory of Crap on the Ocean Floor

InkfishBy Elizabeth PrestonMay 2, 2014 6:09 PM

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Going to the bottom of the ocean isn't such a big deal. Sure, James Cameron generated a lot of fuss last year with his record-breaking descent into the Mariana Trench—but Uncle Ben has been to the deep sea without even using a sub. Yes, that picture shows a packet of Uncle Ben's microwaveable rice a kilometer deep in the Atlantic Ocean. It's one of the items an international group of scientists found in their detailed inventory of underwater garbage. The scientists pooled data from 588 different surveys of the seafloor, covering 32 European sites. The studies had taken place in the Atlantic and Arctic Oceans and the Mediterranean Sea between 1999 and 2011. Some were surveys by remotely operated vehicles, scanning the seabed with video cameras. Others were brute-force sweeps with trawling nets. From all this, a few patterns emerged. First, surprising no one, was plastic. Forty-one percent of all the trash items found were plastic. And that's not even counting plastic nets or fishing lines, which were grouped together with fishing gear (34% of items). Glass bottles made frequent appearances, although glass only accounted for 4% of the trash. There was also wood, paper, cardboard, fabric, and some mystery materials. Coming in at 1% of garbage items was "clinker," the rocky leftovers of burned coal. Steamships used to dump this material overboard between the 18th and 20th centuries, and it still crisscrosses the Mediterranean in the shadows of old shipping routes. The researchers found especially high amounts of clinker in deep sea basins and continental slopes, though they note that there's probably even more of it hidden under a century's worth of sediment on the seafloor. From plastic bags to used coal to Heineken cans (and more plastic bags), much of the trash was sadly expected. For most sites, "the concentrations were pretty much what we expected to find," says lead author Christopher Pham, a PhD student at the University of the Azores in Portugal. However, there was more debris in the Arctic than they thought they'd see—something "we are still trying to explain," he adds. Looking at sites all around Europe gave the scientists a glimpse of the forces that push and pull debris through the oceans. Some bits of refuse sink right away, while others float for long distances before succumbing. The authors found lots of fishing debris on underwater mountains, ridges, and banks, which are areas targeted by commercial fishers. They also found a general increase in litter closer to shore, but low concentrations on continental shelves, Pham says, as currents presumably push trash off of them and into deeper waters. It makes sense, then, that ocean canyons held the most garbage. These sites are dead ends for a drifting bit of junk. Pham thinks more hotspots and accumulation patterns will emerge as scientists survey the seafloor across the rest of the world. One thing scientists probably won't find is a pristine space. "What was shocking was that all of the sites sampled had debris," Pham says. Whether they were looking 35 meters or 4500 meters (almost 3 miles) deep, the researchers found trash. Everywhere in the ocean there are tiny grains of plastic waiting to be eaten by tiny organisms; drifting bags that will be gulped down by sea turtles mistaking them for jellyfish; plastics containing toxic chemicals that can gradually travel up the food chain to humans. There are nets wrapped around corals. There are fish killed by "ghost fishing," the work of discarded fishing gear without a person at the other end. Still, Pham isn't too gloomy. "I'm convinced there is still hope!" he says. "The solution is rather simple," Pham says; "we need to produce less and recycle more." That's simple to say, but not so simple to enact on a global scale. It also doesn't address the question of cleaning up the trash that's already in the ocean. Maybe the next time James Cameron goes down there, he can pick some up. Images: (both) National Oceanography Centre, UK.

Pham, C., Ramirez-Llodra, E., Alt, C., Amaro, T., Bergmann, M., Canals, M., Company, J., Davies, J., Duineveld, G., Galgani, F., Howell, K., Huvenne, V., Isidro, E., Jones, D., Lastras, G., Morato, T., Gomes-Pereira, J., Purser, A., Stewart, H., Tojeira, I., Tubau, X., Van Rooij, D., & Tyler, P. (2014). Marine Litter Distribution and Density in European Seas, from the Shelves to Deep Basins PLoS ONE, 9 (4) DOI: 10.1371/journal.pone.0095839

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