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Tracking plastic in the oceans

Researchers found this net and other debris floating in the Great Pacific Garbage Patch.

Credit: 

©Scripps Institution of Oceanography

The garbage patches floating in the oceans are not solid, giant floating islands of trash. In fact, most of the plasticsx are tiny fragments called microplastics.

Credit: 

©Scripps Institution of Oceanography

Plastic can affect everything from tiny invertebrates to fish to large marine mammals.

Credit: 

©Scripps Institution of Oceanography

Despite worldwide efforts to curtail plastic use — to ban plastic grocery bags, to switch to reusable water bottles instead of disposable plastic bottles, and to get rid of the microplastics in cosmetics, for example — we still produce more than 260 million tons of plastic each year. Almost a third of that plastic goes into disposable, one-time-use items. Only about 1 percent of it is recycled globally, so much ends up in landfills. Worse still, some of the plastic winds up in the world’s oceans.

No one knows exactly how much plastic is in the ocean. Studies over the past few decades have suggested that millions of square kilometers of ocean surface may be covered with floating garbage “patches.” And there are at least five known patches: three in the Pacific, including the Great Pacific Garbage Patch that floats near Hawaii, a patch near Baja California, and one near Chile; and two in the Atlantic, including one in the North Atlantic near Bermuda and one between South America and South Africa. The Great Pacific Garbage Patch is perhaps the best known, estimated by some researchers to be roughly the size of Texas.

All of these patches pose problems for researchers trying to study them.

For one thing, no one is yet sure how long plastics take to degrade completely, or even if they do. Researchers have been studying the breakdown of plastics for the last 20 years. But unlike the relative convenience of studying the effects of plastic degradability in landfills, the problem of studying the fate of plastic in the oceans is complicated. Currents and waves are constantly moving and churning the plastic, breaking it down over time into smaller fragments that are weathered by ultraviolet rays or eaten by marine life. It is also difficult to obtain samples from great depths (the plastics, after all, do not just float on the surface). In the past half decade or so, a number of research teams have ventured into the garbage patches — which are not like solid, floating islands but are far more diffuse, barely visible to the eye. The goals are to identify and quantify what’s in these patches, to clarify how fast they’re growing and how fast the plastics degrade, and to determine how the plastics are affecting marine ecosystems.

Building the Patches

Plastics — and other garbage — wind up in the oceans through myriad ways. They can be blown or washed out to sea from coastlines. They can be carried out to sea by rivers and streams. They can be dumped or spilled overboard from ships. By some estimates, thousands of enormous shipping containers fall off ships each year, spilling their contents into the oceans. Extreme natural events such as hurricanes, tornadoes, tsunamis, floods and mudslides can carry enormous quantities of debris far out to sea. The Japan tsunami last March, for example, sent an estimated 20 million to 40 million tons of debris into the Pacific.

In a 2005 report, the U.N. Environment Program (pdf) estimated that more than 13,000 visible pieces of plastic litter were floating on every square kilometer of ocean. Eighty percent of the plastic in the ocean comes from land-based sources and 20 percent from ocean transportation, such as military fleets, research vessels, cruise ships and fishing boats, in addition to shipping fleets. All of that plastic, however, is not evenly spread out.

When plastic and other garbage enters the ocean, it floats along until it reaches currents that carry it along into giant “pools” called gyres, which are vast rotating currents. There are five major gyres: two in the Pacific, two in the Atlantic and one in the Indian Ocean. They act like giant whirlpools, gradually moving any floating debris toward the gyre’s center, where it is concentrated and trapped. The debris can eventually escape: As wave action and ultraviolet light break it down into smaller pieces, it becomes weighted down with microbial biofilms and sinks. Once in deeper waters, it can be transported by deep currents out of the gyre and away from the patch.

Examining the Plastics

One of the first researchers to raise public awareness about the enormous amount of plastics floating freely in the Pacific Ocean was marine environmental researcher Charles Moore, founder of the Algalita Marine Research Foundation in Long Beach, Calif. In his 2011 book “Plastic Ocean,” Moore recalls that in the summer of 1997, after racing his 15-meter catamaran across the Pacific, he and his crew decided to take a side trip on the journey from Hawaii to California through the North Pacific Subtropical Gyre.

Moore was curious as to what he might find there. What he discovered was almost beyond belief, he says. During the seven days it took to get through this region of the Pacific, Moore and his crew saw an endless sea of floating garbage — mainly in the form of plastic debris. The larger debris could be seen easily at the surface, with smaller particles appearing lower in the water column. Moore suspected the debris floating at the surface was just the tip of the iceberg. This vast area now dubbed the Great Pacific Garbage Patch is estimated to cover between 700,000 and 15 million square kilometers.


Read the rest of this story in the February issue of EARTH, now available for download.

Barry E. DiGregorio
Tuesday, January 24, 2012