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GREEN CITY If a plastic soft drink bottle got tossed into the San Francisco Bay and swept out under the Golden Gate, it might end up in the massive junkyard-at-sea that swirls through a current known as the North Pacific Subtropical Gyre.

Nicknamed the Plastic Vortex, this massive collection of marine debris circulating in a remote area northeast of Hawaii is a sort of watery graveyard for all manner of human refuse. The ocean churns the waste, disintegrating the debris into bits and turning it into something more like plastic soup than a buoyant mass. Ocean experts say it's a very big problem — the gyre is about twice the size of Texas and taking in more garbage all the time — and is only getting bigger.

This gigantic manmade mess — which exists in international waters not regulated by any particular governmental body — presents a slew of difficult questions. What long-term effects is it having on the marine ecosystem? Is there any way to clean it up? Are minuscule plastic particles and their hitchhiker toxins circulating back to people's dinner plates via bioaccumulation?

These are just a few of the mysteries that a crew of researchers hope to unravel during an ocean voyage called Project Kaisei. The Kaisei (Japanese for "ocean planet") is a 151-foot brigantine that sailed out of the San Francisco Bay Aug. 4 for a month-long venture into the plastic vortex.

The tall ship, the second of two research vessels commissioned for Project Kaisei, is operated by the Ocean Voyages Institute, a Sausalito-based nonprofit. Its counterpart, the New Horizon, is operated by the Scripps Institute for Oceanography and departed several days earlier from Southern California.

Project Kaisei spokesperson Ryan Yerkey describes the mission as a multipronged effort. Scientists' first goal is to get a "snapshot" of the effects the garbage is having on the marine ecosystem. "These materials, they never really dissolve," Yerkey explains. "They don't just become part of the ocean. They break down at different degrees. Things like a plastic bag — it breaks down in the heat, and the sun and the water. And a lot of this stuff is so minute that it's getting ingested by fish."

Project Kaisei researchers will also test various technologies that might help them chart a course for cleanup. One idea — using reprocessing technology that has never been tested at sea — is to convert the marine debris from trash to fuel. "We're testing the various reclamation and harvesting technologies," Yerkey explains. "We'd love to be able to get that technology onboard our future vessels out there so they would be able to fuel future missions with the very trash they're collecting." The third goal will be to educate the public about preventive actions like recycling, since an estimated 80 percent of marine debris originates on land.

Algalita, a Long Beach-based marine research foundation, has conducted eight voyages in a 50-foot catamaran to study the Pacific Gyre. "Last year, in February, we were doing a night trawl — that's when a lot of the marine life come up to feed," explains Marieta Francis, executive director of Algalita. "We caught hundreds of these small, six-inch fish, so we thought this was the perfect opportunity to study them. And one of those little fish had 84 pieces of plastic in its stomach."

Over the course of a decade, Algalita has taken hundreds of water samples from the gyre — and not a single one was plastic-free. There are believed to be two giant garbage patches in the Pacific, but the scope of the problem is only beginning to be understood, Francis says. "Now we feel, along with other researchers and even [the National Oceanic and Atmospheric Administration] that there are not two distinct patches, and that in between the two areas where it seems to be accumulating, there is sort of a superhighway that's also collecting the debris."