June 6, 2013
Deep Sea Trash Accumulating Up To 4,000 Meters Below Surface, Says Study
Brett Smith for redOrbit.com - Your Universe Online
For years, people have known about the amount of human-generated trash that ends up in the ocean, but a new study in the journal Deep-Sea Research I: Oceanographic Research Papers showed just how deep our detritus sinks, particularly in the waters around Monterey, California.
"We were inspired by a fisheries study off Southern California that looked at seafloor trash down to 365 meters,” said lead author Kyra Schlining, a senior research technician at the Monterey Bay Aquarium Research Institute (MBARI).
Scientists from the MBARI examined 18,000 hours of underwater video collected by cameras on the institute´s remotely operated underwater vehicles in search of man-made debris along the ocean floor.
“We were able to continue this search in deeper water — down to 4,000 meters,” Schlining said. “Our study also covered a longer time period, and included more in situ observations of deep-sea debris than any previous study I'm aware of."
The videos had been used to identify objects and animals that appeared in these videos and record them in the MBARI´s Video Annotation and Reference System (VARS). In the latest study, Schlining and her colleagues combed through the database to locate video clips of rubbish on the seafloor. They were able to identify over 1,500 observations of deep-sea debris, from sites near Vancouver Island to the Gulf of California to the Hawaiian Islands.
The researchers said they focused their attention on seafloor debris in and around Monterey Bay. They were able to note over 1,150 pieces of debris in these waters alone. In particular, they found that steep, rocky slopes were magnets for trash. The researchers speculated that ocean currents flowing past these rocky projections help to deliver detritus there. They also found that trash was fairly common in the deeper parts of the canyon, below 6,500 feet.
"I was surprised that we saw so much trash in deeper water,” Schlining said. “We don't usually think of our daily activities as affecting life two miles deep in the ocean."
"I'm sure that there's a lot more debris in the canyon that we're not seeing,” she added. “A lot of it gets buried by underwater landslides and sediment movement. Some of it may also be carried into deeper water, farther down the canyon."
According to the report, about one third of the trash was made of plastic. Of these objects, over 50 percent were plastic bags. Metal objects were the second most common type of debris and about two thirds of these objects were aluminum, steel, or tin cans. Other debris included fishing equipment, glass bottles, and cloth items.
“The most frustrating thing for me is that most of the material we saw — glass, metal, paper, plastic — could be recycled,” Schlining noted.
The near-freezing water, lack of sunlight, and low oxygen concentrations where this deep-water trash is located creates highly inhospitable conditions for bacteria and other microorganisms that can break down debris, meaning a plastic bag or soda can float around for decades or longer.
"Ultimately, preventing the introduction of litter into the marine environment through increased public awareness remains the most efficient and cost-effective solution to this dilemma,” the scientists´ report concluded.
Last year, a Scripps study found that plastic trash is accumulating in the “Great Pacific Garbage Patch” at an alarming rate and damaging marine ecosystems as it grows.