Researchers have confirmed widespread plastic pollution across areas of the Caribbean and the Northwest Atlantic Ocean. First announced at the Ocean Sciences Meeting in Portland, Oregon, United States in February 2010 (see BBC) the two-decade-long study is published in Science today.
“It is the most extensive description of plastic in the North Atlantic Ocean” says Kara Lavender Law, a physical oceanographer at the Sea Education Association and lead author of the study.
The plastic in question is swirling around a vortex of ocean currents called the North Atlantic Gyre and, according to the researchers, is comparable in size to the better-known ‘Great Pacific Garbage Patch’ (now immortalised in this Dilbert cartoon). The study was led by the Sea Education Association in Woods Hole, Massachusetts which has monitored the Western Atlantic for 22 years (1986 to 2008).
Following annually-repeated cruise tracks, the sea surface has been routinely sampled for plastic and other debris using towed nets. After 6,100 tows, and using computer simulations to model the ocean circulation, the researchers have shown the plastic piles up where wind-driven surface currents converge.
“The plastic is following the physical currents,” explains Law “and it accumulates in the North Atlantic Gyre.”
But how did scientists detect the plastic dumping ground? “It’s a common misconception that we can see the plastic from space,” says Law “There is no trash island out there.”
The problem is that as it is exposed to UV light and to the physical environment – including wave action, surface winds and currents – the plastic rubbish breaks down. The only remains are tiny pieces, bearing no resemblance to the bags, boots and bottles they started out as. So the researchers found the plastic by picking through trawl samples and sorting the tiny plastic particles manually.
But the study reports that plastic debris is no longer accumulating and has in fact levelled off in recent years. This appears to contradict the trend for rising human populations and plastic usage. With plastic already accounting for 80% of marine debris it might be expected that plastic pollution in the ocean gyres would increase as usage (and disposal) increased.
There could be many explanations for this.
“Firstly we only sample the surface ocean. This does not account for any plastic that may have been driven down by strong winds deeper into the mixed layer,” Laws says. “Secondly, although we use fine nets, some microscopic plastic particles may slip through.”
The team of researchers have also found some marine organisms (including small invertebrates) using the plastic as a substrate which would increase the density and make the naturally buoyant plastic (polyethylene, polypropylene, polystyrene) sink still further (see companion study in Marine Pollution Bulletin). This could take it out of the depths sampled in this study.
It is also currently unknown how the tiny plastic particles that may escape the researchers net might impact the ocean ecosystems. But evidence suggests some commercially fished organisms are accumulating the plastic in their stomachs.
Not only this but toxins can also build up in some plastic, Law explains, and may bio-accumulate in fish we eat.
Image: Plastic pieces collected in a surface plankton net tow / SEA / Giora Proskurowski