For years scientists have been trying to figure out how much plastic trash may be adrift in the planet’s oceans, but new research suggests their estimates may have drastically underestimated the problem.

Oceanographer Giora Proskurowski ventured into the North Atlantic with a group of researchers last year, and took water samples from the surface and from depths as far as 33 metres.

The results were unexpected.

"Almost every tow we did contained plastic regardless of the depth," Proskurowski said in a press release.

Their data, published this week in the journal Geophysical Research Letters, found that tiny bits of plastic suspended across large tracts of the North Atlantic have "emerged as a major open ocean pollutant."

According to Proskurowski and his colleagues, previous studies on the problem may have seriously underestimated the amount of minute plastic particles in the oceans because they didn’t account for the effect of strong winds that can drive plastic below the ocean’s surface.

Measurement problem

Studies that skim the surface for garbage will misjudge the amount of plastic in the area by a factor of 2.5, on average, the researchers say. But if it’s a particularly windy day, there could be as much as 17 times more plastic in the water than would be detected at the surface.

"That really puts a lot of error into the compilation of the data set," said Proskurowski, who is a researcher at the University of Washington.

The results suggest that the Pacific garbage patch, discovered in 1997 off the coast of California, and a similar swath of plastic bits uncovered in 2010 in the North Atlantic, could be much larger than first thought.

Some experts believe the plastic fragments, which can be impossible for fish to distinguish from plankton, are dangerous in part because they sponge up potentially harmful chemicals circulating in the ocean.

Plastics have entangled birds and turned up in the bellies of fish. A paper cited by the U.S. National Oceanic and Atmospheric Administration says as many as 100,000 marine mammals could die trash-related deaths each year.

Another concern is that the plastic particles can carry bacteria and algae to new regions of the oceans where they could become invasive.

As much as 80 per cent of marine debris comes from land, according to the United Nations Environmental Program.

With files from Associated Press