Ocean Plastic’s Mystery Ending

Posted by Jonathan Waterman in NationalGeographic.com on October 22, 2012

Hull of the Robert C. Seamans (right) with the MOCNESS net plunging to 30 feet below the surface. Photo by Jonathan Waterman

As we continue sailing west, we have more questions than answers about our plastic quarry.  We’re now more than halfway to Hawaii, with California 1,200 miles and 17 days behind us. While we’ve conducted more than 40 net deployments and counted close to 40,000 pieces of plastic in the North Pacific gyre, researchers at Sea Education Association (SEA) and elsewhere cannot say for any certainty what happens to the floating plastic.

The plastic could linger in the ocean for an indeterminate number of years, but no one can say how long it takes the plastic to disappear from the surface and what happens next.  In the Atlantic Ocean, particle traps have been placed deep in the water column near Bermuda, and despite the presence of floating plastic in the region, researchers have not detected plastic in the traps.

To move closer toward the answers, it’s useful to look to the Atlantic Ocean, where plastic research has been conducted for more than a quarter century.  A paper by SEA scientists and collaborators, “Plastic Accumulation in the North Atlantic Subtropical Gyre,” published in Science in August 2010 is insightful.  Their data came from more than 6,136 surface tows that were conducted onboard SEA’s sailing research vessels from 1986-2008, from which more than 64,000 plastic pieces were handpicked and counted.  One could expect that these data would show that plastics are increasing in our oceans.  After all, plastic has become ubiquitous and in demand over the last couple of decades.  For instance, beginning in 1950, half a million tons of plastic were created in Europe.  This number has increased more than 500-fold in just 50 years, now they are producing over 260 million tons of plastic.  Although the Marine Pollution (MARPOL) legislation of 1988 prevents the dumping of plastic in the ocean, plastic use is increasing and that plastic ultimately ends up somewhere, either in a landfill or in the ocean.  A 2002 New Zealand report summarized that MARPOL is “widely ignored” and ships alone dump 6.5 million tons of plastic a year into the world’s oceans.  The Science paper documents a five-fold increase in plastic production worldwide during the period of the Atlantic plastic collections studied.

This plastic abundance makes the paper’s conclusion all the more startling: “Despite a strong increase in discarded plastic, no trend was observed in plastic marine debris in the 22-year data set.”

So if the surface-level plastic isn’t increasing in the oceans, is it biodegrading?  According to a study “Degradation of Plastic Carrier Bags,” published recently in Marine Pollution Bulletin, only biodegradable bags breakdown quickly.  Compostable polyester bags, according to this study, degraded completely after 40 weeks in the sea.  The majority of plastic bags used are not compostable or biodegradeable, and are made of materials such as polyethylene which degraded by only 2% in that same amount of time.  It should be noted that most biodegradable or compostable plastics are made to compost in a hot landfill rather than in a cold ocean.  Added to that is the fact that degradation in the sea involves sunlight and most of these UV rays are blocked and absorbed by barnacles or other biomass growing on the plastic—slowing degradation.  Eventually, these plastics are reduced to smaller pieces, such as the micro-plastic soup we’ve encountered here in the Pacific.

“There’s no reason why plastic couldn’t break down to a molecular level and exist as finer and undetectable particles in the water,” says Greg Boyd, an SEA employee and researcher onboard the Robert C. Seamans (RCS).  Greg’s hypothesis is a work in progress, but it could explain why plastic—at least when harvested through net tows—doesn’t appear to be increasing in our oceans.  Microbes also create biofilms over plastic and this might cause the plastic to sink.  At the same time, there is evidence (seen through electron microscopes as “pitting” marks on plastic) to suggest that microbes could potentially be physically degrading or even “eating” the plastic.

Aboard the RCS, our experience in the gyre has shown us something different about where the plastic is found.  Through every-other-day use of the MOCNESS tow (which opens nets at four different depths in the ocean to collect plastic), we’ve found that plastic is not just limited to the surface zone.  Although the plastic levels are thick in windrows where currents and wind combine to create alleyways of plastic flotsam on the surface, MOCNESS harvests have shown us that the wind is also forcing plastic down to 30-foot depths.

So we continue to pitch and roll through this bluest of gyres, hove to for the last two nights to slow down so that we can complete the research.  We’ve ducked around several low-pressure systems and hit only minor squalls, and more than few nights the seas have forced us to brace tight in our berths and on deck.  We’ll continue to harvest both surface and subsurface samples from the water in hopes of unveiling more of the mystery of plastic’s end.

Between net deployments I cornered Emelia DeForce, PhD, and Chief Scientist on the RCS, to ask if we’ll find anything new.  Like many of the sailor researchers, she’s a few nights shy on sleep, but enthusiastic and salty to the core:  “Hell yeah,” she replies, with a huge smile, as the stern sits down with another hard boom against a swell.  “Ultimately we’re getting closer to tracking how wind, wave, and current energy transports plastic in the North Pacific subtropical gyre.  This is what we came for, all of our freakin’ hard work is coming together!”