SAN FRANCISCO – The problem of plastic pollution in the ocean is even worse than anyone feared. Tiny broken up pieces of plastic – microplastic – aren’t just floating at the water’s surface but are pervasive down thousands of feet. There’s actually more microplastic 1,000 feet down than there is in the Great Pacific Garbage Patch, research published Thursday found.

“We didn’t think there would be four times as much plastic floating at depth than at the surface,” said Kyle Van Houtan, chief scientist at the Monterey Bay Aquarium.

He's one of the authors of the study published in this week’s edition of Scientific Reports from the journal Nature that investigated just how much plastic there is in the ocean’s depths.

Literally tons of plastic trash wash down rivers and out to sea each day, fouling the surface and endangering sea life. It's long been believed that most of it floated. But when the researchers looked deep below the surface, they found tiny broken-down plastic pieces, smaller than rice grains, wherever they looked.

The issue of plastic ocean trash has been a focus of public concern over the past decade, a concern that's centered on the Great Pacific Garbage Patch. That's a huge floating blob of plastic trash halfway between California and Hawaii drawn together by ocean currents to create a gyre. This vortex of waves concentrates the floating trash pieces in an area twice the size of Texas.

It's important to remember that the patch isn’t composed of big floating rafts of trash, but rather a pervasive almost mist of tiny bits of plastic floating in the water. Think of it more as a fog in the water than as a bleach bottle bobbing along.

That same fog of plastic bits extends deep down below the surface, the scientists found. And deeper down, it's worse than at the surface.

Previous research found concentrations of microplastic in the Great Pacific Garbage Patch were about 12 particles per cubic meter of water. “We topped out at 16,” said Van Houtan of his team's underwater findings.

The deep-sea methods they used were highly innovative, and confirmed a bleak picture of what the last decade’s research has been pointing toward, said Brendan Godley, a conservation scientist who studies plastic ocean pollution at the University of Exeter in the United Kingdom.

“Scientists are now beginning to realize that microplastics are truly ubiquitous. They’ve been found from the seafloor to the mountain tops, in the air we breathe and in the salt we put on our meals,” he said.

The biggest shock of all, says Peter Ross, a toxicologist who studies the impacts of microplastics on marine life at Canada's Vancouver Aquarium in Vancouver, British Columbia, is that it's not a surprise at all how much plastic there was even deep down in the ocean.

“This research demonstrates the way in which we’ve gone from zero understanding of the problem 15 years ago to full-fledged appreciation that this pollutant is completely distributed around our entire planet,” he said.

What they found

The researchers used drone micro-submarines to sample the water from the surface all the way down to the ocean floor, 3,200 feet. The sample area included one site near Monterey Bay on the California coast and one site 15 miles offshore.

The highest concentrations of microplastics were between 600 and 2,000 feet down.

They also inspected the guts of red pelagic crabs and a kind of jellyfish-like filter feeders called a giant larvacean. Both species play key roles in ocean food webs, from the surface to the seafloor. Every one of them contained plastic.

“Even if you don’t care about the crabs and the larvaceans, they’re the food of things you do care about – tuna, seabirds, whales and turtles all feed on them, or feed on things that feed on them,” said Anela Choy, a professor at the Scripps Institution of Oceanography at the University of California, San Diego and one of the paper’s authors.

While they sampled just two areas, Van Houtan believes they would find similar patterns given ocean currents and the ongoing mix of waters.

Laser spectroscopy allowed them to analyze what kind of plastic each of the particles they found came from, which also turned up some surprises.

Some have suggested that the majority of plastic in the sea comes from discarded or lost commercial fishing gear. However the researchers found that very few particles were from fishing gear. Almost all were from terrestrial sources.

The one piece of good news Van Houtan found in what they saw was that the single largest type of plastic they found floating in the water – about 40% – came from single-use plastics such as beverage and food containers.

“That’s something we as consumers can do something about,” Van Houtan said. “Single-use products are something that we can demand better alternatives for.”