Researchers have been visiting locations in the western North Atlantic Ocean and Caribbean Sea for more than two decades to better understand the large patches of plastic that have formed there. Although the mysteries surrounding exactly how the plastic gets to these locations, where it comes from and what impact it's having on marine life remain unanswered, a team of scientists has now published perhaps the most analytical study of the patches to date based on data collected by research vessels over a 22-year period, between 1986 and 2008.

The researchers from Sea Education Association (SEA), Woods Hole Oceanographic Institution (WHOI) and the University of Hawaii (UH) found, among other things, that the amount of plastic picked up by the researchers' nets remained pretty stable over the years, despite society's increased production and consumption of plastic, according to research published in Thursday's issue of Science Express.

More than 64,000 individual plastic pieces were collected at 6,100 locations that were sampled yearly over the course of the study. To collect these data, ships towed nets along the water's surface at each location, and researchers used tweezers to pick the small plastic bits out of the algae and other collected material. More than 60 percent of the surface plankton net tows collected buoyant plastic pieces that were typically millimeters in size. The highest concentrations of plastic were observed in a region centered at roughly the latitude of Atlanta.

By combining their measurements with a computer model of ocean circulation, the researchers report that this concentration of plastic occurred in an area where wind-driven surface currents were converging. The researchers think this helps explain why the debris accumulates in this particular region, so far away from land. The authors propose a handful of possible explanations for why the patch hasn't grown rapidly since its discovery. The plastic there may break up into pieces too small to be collected by the nets, or it might be sinking beneath the surface. Or, it might be consumed by marine organisms. More research will be necessary to determine the likelihood of each scenario, the researchers conclude.

Several expeditions launched over the past year indicate that the Pacific Ocean is likewise afflicted by large islands of floating garbage. The plastic trash that makes up the Great Pacific Garbage Patch has become a become a popular snack bar for the local Laysan albatross (Phoebastria immutabilis) population, a team of researchers led by the University of Hawaii reported in October 2009. The researchers found that colonies of the birds living near two different garbage patches were eating lighters, fishing line and oyster spacers likely discarded at sea by those in the fishing industry as well as more commonplace trash. One Kure Atoll chick that died was found to have 306 pieces of plastic inside of it, according to the researchers.

Project Kaisei—a team of scientists, sailors, journalists and government officials funded in part by international recycling companies—likewise visited the Great Pacific Garbage Patch a year ago. The crews of the Kaisei and a second ship (the New Horizon, launched from San Diego's Scripps Institution of Oceanography) looked at how decomposing plastic over the past few decades has mixed with phytoplankton and zooplankton and investigated whether netting techniques might be used to clean it up. These researchers noted another reason why a plastic patch may not appear to grow over time: much of the plastic is broken down in a soupy mix that tends to move around as ocean currents and storms produce swells and wind over the course of a given year.

A team of researchers from the Algalita Marine Research Foundation in Long Beach, Calif., returned from its own two-month voyage to study the garbage patch last August humbled and disheartened by what they saw. Project videographer Drew Wheeler concluded: "We must stop this from getting worse by reducing or eliminating the use of non biodegradable plastic for disposable products and product packaging. If the increasing rate of plastic in the ocean does not change, then I do not see how we can avoid catastrophic changes in the health of our marine ecosystem and, as a result, to human life itself."

Image of surface plankton net being towed through the water to collect microscopic organisms and plastic marine debris courtesy of SEA/Gloria Proskurowski