Ocean Garbage Patch Still a Mystery

Jeremy Hsu livescience.com Yahoo News 19 Aug 10;

A vast patch of garbage spanning a swath of the Atlantic Ocean has long puzzled scientists who wondered where the plastic bits came from and why there's not more of it.

Now an exhaustive study, resulting in more than 64,000 bits of plastic collected from the Atlantic Ocean over two decades, has allowed scientists to "go through the garbage" and get to the bottom of some of the mysteries.

Scientists have been particularly mystified over why the concentration of plastic in the Atlantic has not increased during the past 22 years, despite both plastic production and plastic trash increasing during that time period. Still, they have their suspicions.

"I think it's certain that the plastic is breaking down into pieces smaller than what we capture in the net," said Kara Lavender Law, an oceanographer with the Sea Education Association at Woods Hole, Mass.

As bacteria and other organisms built up on the plastic, the added weight may have dragged the debris down to lower ocean depths, according to Lavender Law and her colleagues in a study detailed in the Aug. 19 issue of the journal Science.

Sizing up the trash

Ships towing long nets found the plastic pieces floating across hundreds of miles of the North Atlantic during the past 22 years. The nets only snag objects bigger than a third of millimeter, which can include plankton, seaweed and even tarballs from oil.

The sheer scale of the affected area could rival that of the "Great Pacific Garbage Patch," although Lavender Law cautioned that both regions remain poorly defined. For instance, the exact eastern boundary of the Atlantic region remains undiscovered.

"It's entirely possible that it reaches almost all the way across the Atlantic," Lavender Law told LiveScience.

The affected region in the western North Atlantic Ocean and Caribbean Ocean stretches east to west between Cuba and Virginia, where a combination of wind-forced ocean circulation and the so-called Coriolis Effect of the Earth's rotation keep the plastic circling almost endlessly.

What lies on the surface

The term "garbage patch" does not necessarily mean a visible island of trash floating on the waves, researchers said. Only 62 percent of net tows by ships have contained detectable amounts of plastic.

"What we're collecting are really small fragments of plastic from larger consumer items," Lavender Law explained. "If you're on the deck of a ship, you normally can't even see the plastic pieces."

Each half-hour net tow typically turned up just 20 plastic pieces equivalent to about 0.3 grams in all. By comparison, a U.S. nickel weighs 5 grams.

The vast majority of plastic pieces caught in the net turned out smaller than 10 millimeters, Lavendar Law said. She pointed to a companion study published in this week's issue of the journal Marine Pollution Bulletin that includes all the details on the plastic pieces.

But the unusual discovery of a five-gallon bucket harbored a special surprise - trigger fish, which normally live around ocean reefs. That suggested the fish had found both shelter and perhaps food from the accumulated plastic scum on the bucket.

The more common tiny pieces of plastic can also harbor colonies of bacteria that may not typically belong at the ocean's surface.

"We need to ask if microbes are able to use the plastic as food and degrade it, or if the plastic is acting as substrates for [microbial] communities living on them," Lavender Law said.

How trash travels

The origins of all the plastic remain largely unknown, because researchers currently cannot trace it back to the original location or even the original product that a plastic piece came from.

But ocean circulation studies that use satellite-tracked buoys have found that floating plastic can travel from Washington, D.C., or Miami, Fla., to the Atlantic garbage patch within just 40 days.

The amount of plastic reaching the oceans should have grown in recent decades, according to available data. The amount of buoyant plastics in U.S. Municipal Solid Waste increased by 24 percent between 1993 and 2008, and totaled 14.5 million tons in 2008.

That goes back to the case of the missing trash that should have boosted plastic concentrations in the Atlantic Ocean. Future ship surveys may find more of the plastic lurking in the lower ocean depths, or uncover more about how microbes break down the plastic.

"Understanding the size spectrum and the fate of the plastic is a very important direction to go," Lavender Law noted.

Much of that future research rests upon undergraduate students, who used tweezers to pick out the plastic from the goo pulled up by the plankton nets. More than 7,000 students took part in that painstaking work during the Sea Education Association's SEA Semester annual voyages, which last for a total of three months each year.

"I always want to make sure I give full credit to the undergrads," Lavender Law said. "Undergrads with or without science backgrounds can make real contributions."

Researchers wonder where extra plastic trash is
Randolph E. Schmid, Associated Press 19 Aug 10;

WASHINGTON – The amount of plastic trash in the ocean doesn't seem to be growing, and environmentalists are puzzled.

A 22-year study indicates that the amount of plastic corralled by currents into a floating junkyard in the Atlantic Ocean has not increased.

"We know that global production of plastics has increased substantially over the time period" and disposal also has increased, said Kara Lavender Law of the Sea Education Association in Woods Hole, Mass.

"If there is more plastic trash it's hard to believe more is not making it into the ocean. There is missing plastic out there," she said in a telephone interview.

Over the course of the study more than 64,000 individual plastic pieces were collected at 6,100 locations that were sampled, Law and colleagues report in Thursday's online edition of the journal Science.

Researchers worry about plastic in the oceans because it can endanger seabirds, turtles and other sea life which eat it, or become entangled. A floating trash field also has been reported in the Pacific Ocean.

While the researchers found significant year-to-year changes in the amount of plastic in the Atlantic, averaging over time they found no significant increase.

The annual trips to the Atlantic junkyard use plankton nets to skim the surface, collecting tiny pieces, and students then pick out the plastic pieces with tweezers.

The exact expanse of the Atlantic trash field has not been determined, Law said. It is located in the Atlantic at about the same latitude as Atlanta.

Law suggested that the plastic may be breaking unto smaller pieces and passing through the nets, or that biological growth on the plastic may be causing it to become more dense and sink into the ocean where the nets miss it.

Wind patterns and currents do not seem to have changed, she said, so the trash should still be collecting at the same place.

The research was funded by the National Science Foundation.

Study measures Atlantic plastic accumulation
Mark Kinver, BBC News 20 Aug 10;

A study has measured the amount of plastic debris found in a region of the Atlantic Ocean over a 22-year period.

US researchers, writing in Science, suggest the volume of plastic appeared to have peaked in recent years.

One reason could be tighter marine pollution rules that prevent vessels dumping their waste at sea.

The team said monitoring the free-floating plastic also provided an insight into the behaviour of ocean surface currents.

They found plastic, most pieces measuring no more than a few millimetres, in more than 60% of 6,136 samples collected by dragging fine-meshed nets along the ocean's surface.

The researchers - from the US-based Sea Education Association (Sea), Woods Hole Oceanographic Institution and the University of Hawaii - described plastic as a "major contaminant".

"Plastic marine pollution is a significant environmental concern, yet a quantitative description of the scope of this problem is the open ocean is lacking," they wrote.

"Their chemically engineered durability and slow rate of biodegradation allow these synthetic polymers to withstand the ocean environment for years to decades or longer."

The impacts caused by the debris include:

* sea animals becoming entangled
* seabirds and other marine creatures eating the plastic
* the debris being used as a "life raft" by some species to reach areas outside their normal distribution range

"While high concentrations of floating plastic debris have been found in the Pacific Ocean, only limited data exist to quantify and explain the geographical range," they said.

"In the Atlantic Ocean, the subject has been all but ignored."