LOS ANGELES (Reuters) - Ocean scientists recently back from a voyage to the "Great Pacific Garbage Patch" said on Thursday they had found plastic debris strewn across a 1,700-mile (2,700-km) long stretch of open sea.
The research team from the three-week Seaplex expedition said more work remains to be done to determine the full extent of the trash vortex, how it affects marine life and how it might safely be removed from the ocean.
Cleanup will be difficult because the "vast majority of things we saw were small, about the size of your thumbnail or smaller," Miriam Goldstein, the expedition's chief scientist, told reporters at the Scripps Institution of Oceanography in La Jolla, California.
"We found a lot of particles that were about the size of the animals that are living out there, so that would certainly present a challenge to removing those particles," she said.
The 172-foot (52-meter) research vessel New Horizon returned to shore last Friday from a trip to the North Pacific Ocean Gyre, a giant eddy-like expanse of sea about midway between Japan and the West Coast of the United States.
Debris winds up concentrated there by circular, clockwise ocean currents that form an oblong-shaped "convergence zone."
"Our human footprint is now apparent in even one of the most remote places on the planet," said Doug Woodring, director of Project Kaisei, which co-sponsored the Seaplex study.
He joined the New Horizon crew, and his group's ship returns from its own expedition next week. That boat, the Kaisei, has been experimenting with possible debris-skimming cleanup methods, he said.
The existence of the vast, remote debris field, widely referred to as the "Great Pacific Garbage Patch," was first publicized by ocean activist Charles Moore, who discovered the area by accident in 1997.
He has said some of his samples from the area contained six times more plastic by weight than zooplankton. But the exact scope of the phenomenon remains unclear.
Goldstein said the crew of the New Horizon hauled up plastic debris in 100 consecutive surface samples taken across 1,700 miles of the ship's cruise track -- roughly twice the length of the California coastline but just a fraction of the gyre. Relatively little sampling was done beneath the surface.
"We can't necessarily say very much about the extent of the area covered by marine debris," she said.
Scientists will spend months studying samples to determine what harm the plastic may be doing to marine life, much of it tiny, jelly-like organisms classified as zooplankton.
Many such creatures found there are not well known to science, Goldstein said.
During one glassy-calm day at sea, she recalled, the water was littered with plastic specks, "like little flecks of confetti or snow, just floating on the surface, and beneath them you could see these really interesting critters just going about their business."
"So it was, I thought, a very striking combination of a cool, basic science discovery, and then this undeniable sign of human impact," she said.
Editing by Mary Milliken and Todd Eastham