Hundreds of kilometers off the coast of southern California lies the Great Pacific Garbage Patch, a vast soup of degraded plastic fragments. On the other side of the country, tiny flecks of floating plastic swim in a swath of seemingly pristine Atlantic Ocean at least two-thirds the size of the United States. Oceanographers have quantified trends in one of these "plastic soups" for the first time, and they've come to a surprising conclusion: The amount of plastic has remained steady for 2 decades despite a steep rise in industrial plastic production. That suggests that either people are keeping their trash on land or plastic is going to some unknown destination in the sea.
Since 1986, students on research sailing trips led by Sea Education Association (SEA) in Woods Hole, Massachusetts, have been documenting plastic snagged in their plankton nets in the western North Atlantic Ocean and Caribbean Sea. The students and scientists tow a net behind their ship for about 2 kilometers, then use tweezers to pick out and hand-count trapped plastic pieces, most no larger than your pinky fingernail.
In their first publication of these data since the late 1980s, the SEA team reports that it found plastic in more than 60% of 6136 tows over 22 years. The levels are low close to shore but rise hundreds of kilometers off the coast between 22 and 38 degrees latitude (roughly from the Bahamas to Baltimore).
"When you expect to see zero plastic hundreds of miles from shore, it's shocking," says lead author and SEA oceanographer Kara Lavender Law. But the plastic is "relatively dilute," she adds—up to 1000 tiny pieces filtered from the equivalent of 2000 bathtubs of water.
A chemical analysis found that the plastic consists mostly of polyethylene and polypropylene, which are used to make things such as plastic milk jugs and grocery bags. The SEA crews occasionally spot larger objects in the plastic zone, such as buckets and toothbrushes, but they are much rarer.
Co-author Nikolai Maximenko of the University of Hawaii, Manoa, found that he could predict where the plastic accumulates using satellite-tracked data from research buoys deployed from coasts. As in the North Pacific, the area corresponds to a subtropical ocean "gyre," a region where wind-driven currents rotate around a quiet center. Some reports suggest plastic is accumulating in other gyres, for example, in the Indian Ocean.
But despite huge annual fluctuations in plastic levels (probably a result of smaller-scale eddies and winds, Law says), the overall amount of plastic in the North Atlantic Ocean has been steady across the two-plus decades. This is surprising because the amount of plastic produced globally and thrown away in the United States has grown several times over the same period, and presumably some of it winds up in the ocean. Although a 1988 ban on plastic trash dumping by ships may be a factor, Law thinks "there's some sort of missing sink." For example, the plastic might disintegrate into pieces too small to be caught in a net. Or algae-coated pieces might sink to the sediments, or the plastic could be eaten by plankton or fish. That raises the concern that marine animals could be poisoned by toxic chemicals carried by the plastic, the team reports online today in Science.
"This is one of the first truly quantitative reports of the long-term evolution of plastics in the ocean," says Joel Baker, an environmental engineer at the University of Washington, Tacoma. Unlike Law, he wonders whether the constant levels over time could simply reflect "a better job of stewardship" of plastic waste in coastal communities on the U.S. East Coast. But given the scant information on where the plastic is coming from, he concludes: "I think we just don't know."